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IBM PS/2 Model 50 Maintenance Guide: Difference between revisions

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Split combined PS/2 50/60 and 70/80 pages into per-model pages
 
Rewrite in plain prose; cite the 5.5 V battery test (retain tip H024809) to Ardent's 60/65 SX/80 Common Devices page, not the Battery/Speaker Assembly page; replace AT-bus FRU order with IBM HMM Micro Channel codes (p. 36); add HMR battery caution, same-slot rule, H005662, HMM test-table misprint; remove uncited swap and riser claims
 
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This guide documents preventive maintenance for the '''[[IBM PS/2 Model 50]]''' (machine type 8550, both the original Model 50 8550-021 and the Model 50 Z 8550-031 / 061). The Model 50 is a low-profile desktop with the planar mounted to the chassis floor, the drives in a front cage and the PSU on the left.
<templatestyles src="Template:StyledTable/styles.css" />
[[File:IBM PS2 Model 50Z internals.jpg|thumb|right|360px|A Model 50 Z with the cover removed, showing the planar, the drive structure and the drive riser card. (Image: Ruben de Rijcke, CC BY-SA 4.0, via Wikimedia Commons)]]
Routine maintenance on the '''[[IBM PS/2 Model 50]]''' (machine type 8550) covers the original 8550-021 of April 1987 and the Model 50 Z (8550-031 and -061) of June 1988. All three are low desktop units: the planar lies on the floor of the chassis, the drives sit in a plastic structure over it, and the power supply slides onto an edge connector on the planar.<ref name="atcommon50">[https://www.ardent-tool.com/50_70/Common.html "8550 and 8570 – Common Devices"], Ardent Tool of Capitalism. Opening the case ("slide the case forward about two inches then lift up"), Peter Wendt's method for a locked case, closing the case, and removing the planar (drive-structure removal tool under the battery/speaker assembly, three planar screws, three EMC shield screws, 1/8-inch centring pin beside inductor LN2).</ref>


== Safety Warning ==
== Safety ==


The Model 50 PSU is rated 94 W and contains mains-rectified bulk capacitors that hold a lethal charge after power-off. Before any work inside the PSU shell:
The 94 W supply rectifies the mains, and its primary reservoir capacitor holds a lethal charge after the machine is unplugged. Before working inside the supply, discharge that capacitor through a resistor and check with a meter that it has fallen to a few volts. The supply selects its input range automatically, so there is no voltage switch to set.<ref name="m50hmr">IBM, ''IBM PS/2 Model 50 Hardware Maintenance Reference'', S64F-3989-00, March 1990. Hosted on this wiki as [[IBM PS2 Model 50 Hardware Maintenance Reference]] ([[:File:IBM PS2 Model 50 HMR.pdf|PDF]]). Sections 1.1.1 (cover lock), 1.1.2 (power-on password), 1.2.2 (CMOS RAM), 1.2.7 (diskette-drive controller and bus adapter), 1.2.8 (keyboard and pointing-device connectors and fuse), 2.1 (diskette drive identification and media compatibility), 2.2 (Move the computer to park the heads), 3.1 (power supply, sense levels and the green power-good light), 4.0 (specifications), 5.0 (snap tool 72X8547), 6.2 (1010 battery and speaker assembly: caution and warning), 6.4 (1020 adapters: refit in the same slot).</ref>


# Power off and unplug the mains lead.
There is no CRT in the system unit. IBM's 8503, 8512, 8513 and 8514 displays have their own tube and supply; see [[CRT Discharge Procedure]].
# Wait at least 30 seconds.
# Discharge the bulk capacitor through a 1 kΩ / 5 W resistor.
# Verify with a multimeter.


There is no CRT in the system unit (the matching IBM 8503 / 8512 / 8513 / 8514 displays contain their own CRT and PSU and are serviced separately).
== Identifying your model ==


== Identifying Model 50 vs Model 50 Z ==
The machine type and submodel are on the rear label, for example "Type 8550-061".


<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%;"
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Model 50 and Model 50 Z'''
|+'''Model 50 / 50 Z identification'''
! !! Model 50 (8550-021) !! Model 50 Z (8550-031, -061)
! Marker !! Model 50 (8550-021) !! Model 50 Z (8550-031 / 061)
|-
| Announced || 2 April 1987 || 2 June 1988
|-
|-
| Front badge || "PS/2" with "50" || "PS/2" with "50 Z"
| System board || Type 1; FRU 72X8516 || Type 2; FRU 10G4005
|-
|-
| Wait states || 1 || 0
| Wait states || One || None with 85 ns memory
|-
|-
| DRAM speed || 125-ns SIMMs || 85-ns SIMMs
| Memory sockets || Two 30-pin, with two 512 KB modules (FRU 72X8517) || One 72-pin, with a 1 MB module (FRU 90X8624) or 2 MB (FRU 92F0104)
|-
|-
| SIMM sockets on planar || 2 (512 KB modules only) || 1 (1 MB or 2 MB modules)
| BIOS || Four 27256 EPROMs || Two 27512 EPROMs
|-
|-
| Stock HDD || 20 MB ST-506 || 30 MB ST-506 (031) or 60 MB ESDI (061)
| Clock chip || MC146818A at ZM47 || MC146818A at ZM8
|-
|-
| Reference Diskette || Same Model 50 Reference Diskette covers all three submodels
| Fixed disk || 20 MB ST-506 on an adapter || 30 MB or 60 MB with integrated controller on a riser
|}
|}


The rear panel label gives the IBM machine type and submodel (e.g. "Type 8550-061").
Sources: the announcements, IBM's ''Technical Reference'' and parts list, and Ardent Tool's planar maps.<ref name="ann49">IBM Announcement Letter 187-049, ''IBM Personal System/2 Model 50'', 2 April 1987, text at [https://www.ardent-tool.com/8550/187-049.txt ardent-tool.com]. The 8550-021; 94 W automatic voltage-sensing supply; four 16-bit slots with one used by the disk controller; the 1.44 MB drive specification and IBM's instruction not to format a 1 MB diskette as 1.44 MB or a 2 MB diskette as 720 KB.</ref><ref name="ann50z">IBM Announcement Letter 188-080, ''IBM Personal System/2 Model 50 Z Desktop Systems with Improved Hardfile and Memory'', 2 June 1988, text at [https://www.ardent-tool.com/8550/188-080.txt ardent-tool.com]. The 8550-031 and -061; zero wait states with 85 ns memory; 30 MB and 60 MB drives with the controller integrated, 39 ms and 27 ms average access.</ref><ref name="m50tr90">IBM, ''IBM Personal System/2 Model 50 Technical Reference'', October 1990. Hosted on this wiki as [[IBM PS2 Model 50 Technical Reference (October 1990)]] ([[:File:IBM PS2 Model 50 Technical Reference Oct90.pdf|PDF]]). Type 1 and Type 2 system boards, p. 1-3; supply outputs and output protection, pp. 1-11 and 1-12; ROM and RAM subsystems and memory connectors, pp. 3-7 to 3-9.</ref><ref name="hmm">IBM, ''IBM Personal System/2 Hardware Maintenance Manual'', S52G-9971-02, October 1994. Hosted on this wiki as [[IBM Personal System 2 Hardware Maintenance Manual (S52G-9971-02, October 1994)]] ([[:File:IBM PS2 HMM S52G-9971 Oct 1994.pdf|PDF]]). Micro Channel numeric error codes 160–170, with the lithium battery caution, p. 36; Models 50 and 70 power supply connector, p. 141; "Real-Time Clock Problems" and "Running Automatic Configuration", p. 150; Model 50 parts list, p. 240.</ref><ref name="at8550">Louis Ohland, Tomáš Slavotínek ''et al.'', [https://www.ardent-tool.com/8550/Planar.html "8550 Planar"], Ardent Tool of Capitalism. Designator map of planars 90X9161 and 15F6969: F1 250 V 3 A fuse, J1 battery/speaker connector, J9 fan, J10 fixed-disk adapter slot, J11 slot with auxiliary video extension, J15 video, J16 parallel, J17 serial, J19 mouse, J20 keyboard, ZM47 MC146818A, ZM13–ZM16 BIOS in 27256 EPROMs; the Model 50/60 Reference Disk v1.08.</ref><ref name="at8550z">Louis Ohland, Tomáš Slavotínek ''et al.'', [https://www.ardent-tool.com/8550/Planar_Z.html "8550 Z Planar"], Ardent Tool of Capitalism. Designator map of planar FRU 90X9533: F1 3 A 250 V, J2 battery/speaker header, J8 case fan header, ZM8 MC146818A, ZM45 72-pin SIMM socket, BIOS in two 27512 EPROMs; Peter Wendt's method for opening a locked case.</ref>
 
== Opening the system unit ==
 
Tools: a screwdriver and an anti-static wrist strap. IBM supplied a snap tool, part 72X8547, for lifting the plastic snaps inside; it is stored in the system unit in front of the battery and speaker assembly.<ref name="m50hmr" />
 
# Switch off and unplug everything.
# Unlock the cover lock if one is fitted.<ref name="m50hmr" />
# Loosen the two cover screws at the rear. They are captive: when they turn freely they are undone.
# Slide the cover forward about two inches and lift it off.<ref name="atcommon50" />


== Opening the System Unit ==
To refit the cover, place it on the base about an inch back from its final position so that it engages the guide at the bottom rear of the case, then slide it forward. If the diskette drive stops it lining up with the bezel, check that the drive is fully seated on its shelf.<ref name="atcommon50" />


Tools: Philips #2 screwdriver and an anti-static strap. IBM supplied a small plastic "crowbar" tool with the system to release the captive plastic push-pin drive tabs.
If the cover is locked and the key is lost, Peter Wendt's method is to undo the rear thumbscrews, push the cover forward as far as it goes, and lever a gap of 4–5 mm between the cover and the rear wall with a large flat screwdriver so the cover slides over the locking tab.<ref name="atcommon50" /> IBM's own answer is a new cover-lock assembly, which comes with two keys; one of the new keys and a pair of pliers are used to force the old lock.<ref name="m50hmr" />


# Power off and unplug all cables (mains, keyboard, mouse, monitor, parallel, serial).
=== Taking the planar out ===
# Locate the '''two thumbscrews''' at the rear top corners of the chassis.
# Loosen both. The cover slides back about 10 mm and lifts off upwards.
# The drive cage sits over the front of the planar; the MCA riser is at the rear; the PSU is on the left-front.


The hard drive (if fitted) is mounted on a plastic carrier held by '''captive push-pin tabs'''. Pry the tabs gently with the IBM crowbar or a thin plastic spudger. '''Do not''' use a metal screwdriver — the plastic pins crack easily.
Remove the adapter cards, diskette drive, fixed disk and drive riser card, then the fixed-disk adapter and the exhaust fan. Lift all the white plastic snaps, including the one under the speaker assembly, and pull the drive structure straight up. Remove the power supply, the three planar screws and the three screws holding the EMC shield over the rear ports. A 1/8-inch pin in the base locates the planar through a hole beside inductor LN2, so lift the planar straight up without tilting it.<ref name="atcommon50" />


MCA cards are held by '''plastic thumbscrews''' on the rear card bracket — no metal screws to lose.
== Cleaning ==


== Regular Cleaning ==
* Brush and blow dust off the planar, cards, drive structure and fan with low-pressure air. Hold the fan still while doing so.
* The Model 50 supply has no fan of its own and a screen across its underside. Ardent Tool's advice is to clear the lint from that screen.<ref name="atpwr50">Louis Ohland, Tomáš Slavotínek ''et al.'', [https://www.ardent-tool.com/50_70/Power.html "8550 / 8570 / 756x – Power Supply"], Ardent Tool of Capitalism. The 50-pin connector pinout; the test-voltage table (−12 V −9.0 to −15.0 V at pins 2 and 1; +12 V +9.0 to +15.0 V at pins 2 and 3; +5 V +3.7 to +6.2 V at pins 2 and 15), measured with the supply removed and switched on; the ASTEC AA13621 (IBM P/N 90X9527, FRU 90X9366), 94 W; the separate fan that blows out of the rear (Panaflo FBH-09A12L 12 V 0.14 A or Nidec D09B-12PLL 12 V 0.09 A); the lint screen and T10 security Torx screws; removal (two screws at the back, one at the front inner corner); F1 or F2 as the suspect in a supply with no output; Peter Wendt's remark that the 94 W supply is weaker than assumed once upgrades are fitted.</ref>
* PS/2 diskette drives have no shutter over the slot and collect dust. Ardent Tool's contributors report dirt on the Mitsubishi head actuator spindle and loose head-damper pads on ALPS drives.<ref name="atcommon60">[https://www.ardent-tool.com/60_65_80/Common.html "60, 65 SX, and 80 – Common Devices"], Ardent Tool of Capitalism. IBM retain tip H024809 on low battery voltage (battery 72X8498 in speaker/battery assembly 33F5950: remove it from the assembly, measure on the 12 V DC range, replace below 5.5 V DC; intermittent 161, 162 and 163 errors); Alfred Arnold on the clock stopping before the CMOS contents are lost; dust under the supply fan on the Models 60 and 80 causing lost configuration and disk errors; Peter Wendt on ALPS and Mitsubishi diskette drives; the warning that two adapters driving VGA signals damage each other.</ref><ref name="atfdd">[https://www.ardent-tool.com/floppy/8580.html "8580 Diskette Drives"], Ardent Tool of Capitalism, content by Fred Spencer and Al Savage. The diskette controller under the supply fan collecting dirt that leaks current between pins and gives 6xx errors; Peter Wendt on mechanical causes of a 162; Al Savage's drive recap.</ref>
* On the Models 60 and 80, dust under the supply fan over the keyboard controller, clock chip, diskette controller and serial controller has caused lost configuration, a wrong clock and disk errors that a new battery did not cure.<ref name="atcommon60" /><ref name="atfdd" /> The same chips are on the Model 50 planar, so clean that area too.


* Soft brush and low-pressure compressed air for the planar, the MCA riser, the drive cage and the PSU vents.
== Power supply checks ==
* Hold any fan blades by hand if using compressed air to avoid spinning the fan beyond its rated speed.
* Clean each MCA card's edge fingers with a soft eraser or a deoxidising contact cleaner before reseating. MCA contacts oxidise after 30+ years and produce intermittent card-not-detected (POST 165) symptoms.
* Clean the PS/2 keyboard and mouse Mini-DIN-6 connectors with a deoxidising contact cleaner sparingly on a foam swab. Pins on the Mini-DIN connector bend easily; verify pin alignment before reseating.
* Inspect the planar for any signs of leaked electrolyte around any through-hole or surface-mount aluminium electrolytic capacitor. The Model 50 / 50 Z is less affected than the [[IBM PS/2 Model 70]] / [[IBM PS/2 Model 80|80]] by the famous SMD electrolyte leak, but the through-hole electrolytics still age.


== PSU Voltage Checks ==
The supply is an ASTEC AA13621, IBM P/N 90X9527, FRU 90X9366, rated 94 W.<ref name="atpwr50" /><ref name="hmm" /> Its outputs are +5 V, +12 V and −12 V; there is no −5 V output.<ref name="m50tr90" />


Probe the PSU output rails at the planar power connector with a multimeter while the system is powered on.
After the machine has been off for ten seconds or more, the supply raises Power Good at switch-on, once every output is above its minimum under-voltage sense level. Power Good lights the green lamp on the front; if the lamp stays off, the supply is not working properly.<ref name="m50hmr" />


{| class="wikitable styled-table" style="width:100%; text-align:center;"
{| class="wikitable styled-table" style="width:60%; text-align:center;"
|+'''Model 50 PSU rail tolerances'''
|+'''Model 50 under-voltage sense levels'''
! Rail !! Acceptable range
! Output !! Sense level
|-
|-
| +5 V || +4.75 V to +5.25 V
| +5 V || +4.5 V
|-
|-
| +12 V || +11.4 V to +12.6 V
| +12 V || +10.8 V
|-
|-
| &minus;5 V || &minus;4.75 V to &minus;5.25 V
| −12 V || −10.2 V
|}
 
A short on any output, or an internal overvoltage fault before any output reaches 130 % of nominal, latches all outputs off. The supply only restarts once the fault has gone and the switch has been off for at least ten seconds.<ref name="m50tr90" /> A machine that starts and immediately shuts down is therefore as likely to have a short on the planar or a card as a faulty supply.
 
To test the supply itself, Ardent Tool's procedure is to remove it, place it connector-up, switch it on and measure at the 50-pin connector with the negative lead on pin 2:<ref name="atpwr50" />
 
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Model 50 supply test (supply removed)'''
! Output !! + lead !! Minimum !! Maximum
|-
|-
| &minus;12 V || &minus;11.4 V to &minus;12.6 V
| −12 V || Pin 1 || −9.0 V || −15.0 V
|-
| +12 V || Pin 3 || +9.0 V || +15.0 V
|-
| +5 V || Pin 15 || +3.7 V || +6.2 V
|}
|}


The 94 W PSU is borderline for a fully populated Model 50. If you have multiple MCA cards plus an ESDI drive plus optional RAM expansion, expect the +12 V rail to sag under load. The 207 W Model 60 PSU is '''not''' a drop-in for the Model 50 — the planar connectors differ.
IBM's 1994 ''Hardware Maintenance Manual'' prints this table for the Models 50 and 70 with minimums of +15.0 V for +12 V and +6.2 V for +5 V, which are misprints.<ref name="hmm" /> If the voltages are wrong, check the power cord, which can make poor contact in the supply's socket, and then replace the supply. A supply with no output at all may have blown fuse F1 or F2.<ref name="atpwr50" />


== CMOS / RTC Battery ==
The connector carries −12 V on pin 1, +12 V on odd pins 3 to 13, +5 V on odd pins 15 to 47, ground on even pins 2 to 48, System Status on pin 49 and Power Good on pin 50.<ref name="atpwr50" /> The Model 60 supply does not fit: it uses a 15-pin planar connector and separate drive power cables.<ref name="atpwr60">[https://www.ardent-tool.com/60_65_80/Power.html "60, 65 SX, and 80 – Power Supply"], Ardent Tool of Capitalism. The 15-pin planar power connector of the Models 60, 65 SX and 80, and their four-pin drive power cables.</ref>


The Model 50 / 50 Z stores SETUP configuration (memory, drive types, date, time) in 50 bytes of CMOS RAM inside the '''Dallas DS1287 / DS12887''' integrated RTC + battery module on the planar. The lithium cell inside the module fails after 10–15 years, producing the classic POST error cluster:
The fan is a separate assembly on the planar (J9 on the Model 50, J8 on the 50 Z). Ardent Tool reports Panaflo FBH-09A12L (12 V, 0.14 A) and Nidec D09B-12PLL (12 V, 0.09 A) fans; IBM's FRU is 72X8515.<ref name="atpwr50" /><ref name="at8550" /><ref name="at8550z" /><ref name="hmm" /> Peter Wendt warns that the 94 W supply struggles once a processor upgrade, a lot of memory, a SCSI adapter and a high-resolution graphics card are fitted.<ref name="atpwr50" />


* '''161''' — CMOS configuration empty (battery failure).
== Battery and clock ==
* '''162''' — CMOS checksum mismatch.
* '''163''' — Time and date not set.


Replacement procedure:
The clock is a Motorola MC146818A soldered to the planar (ZM47 on the Model 50, ZM8 on the 50 Z). It is powered, when the machine is off, by a 6 V lithium battery in the battery and speaker assembly at the front of the chassis.<ref name="at8550" /><ref name="at8550z" /><ref name="m50tr">IBM, ''IBM Personal System/2 Model 50 Technical Reference'', May 1988. Hosted on this wiki as [[IBM PS2 Model 50 Technical Reference (May 1988)]] ([[:File:IBM PS2 Model 50 Technical Reference May88.pdf|PDF]]). Figure 1-7, "Physical Specifications", p. 1-9 (275 mA keyboard and 300 mA auxiliary port limits); "Real-Time Clock/Complementary Metal-Oxide Semiconductor RAM", p. 3-12 (6 V lithium battery; the cover lock prevents battery removal).</ref> The CMOS RAM holds 64 bytes: 50 for configuration and security information, and 14 used by the clock for the date, time and battery level.<ref name="m50hmr" />


# Power off and discharge the PSU bulk capacitor.
IBM's FRU numbers are 33F5950 for the battery and speaker assembly and 72X8498 for the battery.<ref name="hmm" /> The battery is a two-cell 6 V lithium pack; Ardent Tool lists the CR-P2, DL223A, EL223AP, K223LA and PC223 camera batteries as equivalents.<ref name="atbatt">Ardent Tool of Capitalism, [https://www.ardent-tool.com/misc/batteries.html "PS/2 RTC/CMOS Batteries"], based on content by Bob Eager and Peter H. Wendt. Models 50 and 50 Z: FRU 72X8498, a 6 V two-cell lithium pack in the battery/speaker assembly; equivalents CR-P2, DL223A, EL223AP, K223LA and PC223.</ref>
# Remove the planar from the chassis (4 screws to the chassis floor).
# Identify the DS1287 / DS12887 — a 24-pin DIP marked "DALLAS" near the front-right of the planar.
# Carefully desolder using solder wick and a fine-tipped iron at no more than 350 °C. The planar pads are not very tolerant of repeated heating; limit each cycle to 5–7 seconds.
# Fit either a fresh '''Dallas DS12887+''' (the "+" indicates a fresh manufacture date with a fresh internal cell) or a socket. A socketed solution allows future replacements without further desoldering.
# Reassemble. Boot the Reference Diskette and run SETUP to re-enter memory size, drive types, date and time.


Some restorers cut the DS1287 plastic case to expose the internal cell and connect an external CR2032 holder. This is electrically valid but messier than a clean module replacement.
=== Testing the battery ===


== Connector Care ==
IBM retain tip H024809, which Ardent Tool reproduces for the Models 60, 65 SX and 80, covers the same battery (72X8498) and battery and speaker assembly (33F5950) that the Model 50 uses. It says that low battery voltage or a faulty assembly can cause intermittent 161, 162 and 163 errors, and gives this check:<ref name="atcommon60" /><ref name="hmm" />


* '''PS/2 keyboard / mouse''': Mini-DIN-6 with plastic alignment key. Plugging a mouse into the keyboard port (or vice versa) produces a '''301 keyboard error''' at POST.
# Switch the system off.
* '''Keyboard / mouse fuse''' on the planar (3 A) protects the combined +5 V to the keyboard and pointing device. A blown fuse produces a '''305 keyboard error''' and prevents booting past POST. Replace with the same value and type.
# Remove the battery from the battery and speaker assembly. Measured in the assembly, the reading is not accurate.
* '''Serial port''' (DB-25 male) and '''parallel port''' (DB-25 female).
# Set the meter to the 12 V DC range.
* '''MCA card edge connectors''' — clean both the card fingers and the slot before any work.
# Replace the battery if it reads below 5.5 V DC.


== Single-Cable Drive Interface ==
Alfred Arnold, quoted by Ardent Tool, notes that as the battery fails the clock's 32 kHz oscillator usually stops before the CMOS contents are lost. A machine that powers up showing the time at which it was switched off, with no 161 or 163 yet, has a battery near the end of its life.<ref name="atcommon60" />


The Model 50 uses the PS/2 single-cable drive interface — power and data in one ribbon cable from the planar floppy controller (or from the rear of the MCA hard drive controller card) to the drive. Care points:
=== Replacing the battery ===


* Pin 1 is marked with a coloured stripe on the cable.
IBM's caution: the lithium battery presents a fire, explosion or severe burn risk. Do not recharge it, disassemble it, heat it above 100 °C, burn it or expose its contents to water, and replace it only with part 72X8498. To avoid discharging the battery, take it out before disconnecting the assembly's cable, and connect the cable before fitting the battery.<ref name="m50hmr" />
* Drive power is +5 V and +12 V routed through the planar / controller; no Molex 4-pin connectors.
* Drives have no dust shutter on the front bezel; dust accumulates and contaminates heads. Clean periodically with a head-cleaning diskette.


== Floppy Drive Maintenance ==
To remove the assembly on the Model 50 and 50 Z, press in the retaining clip at the bottom of the assembly (above the orange crystal holder) and push or pull the assembly up, away from the base. On the Model 50 the assembly is also held by its card-edge connector on the planar; the 50 Z uses a 6-pin header. The battery's contacts face the rear, against the spring clips.<ref name="atbsa">Ardent Tool of Capitalism, [https://www.ardent-tool.com/misc/Battery_Speaker_Assembly.html "Battery/Speaker Assembly"]. FRUs 33F5950 and 72X8498; battery orientation; clearing a power-on password on the Models 50, 60, 70 and 80; removing the assembly on the Models 50, 50 Z and 70; the card-edge (Model 50) and 6-pin header (Model 50 Z) pinouts.</ref> Avoid pulling the battery cable off the planar while working elsewhere in the machine, which loses the configuration.<ref name="atcommon60" />


* The Model 50 ships with a 1.44 MB 3.5" half-height drive. Use only DSHD media in this drive.
After replacing the battery, start from the Reference Diskette. Run Automatic Configuration if the machine used default settings, or restore a customised configuration from the backup copy of the Reference Diskette.<ref name="m50hmr" /> IBM warns that Automatic Configuration can overwrite customised settings, so note them with View Configuration first.<ref name="hmm" />
* Clean the head with isopropyl alcohol on a foam swab. '''No cotton-tipped swabs''' — cotton fibres in the head gap cause CRC errors.
* Replace the drive belt if the drive is in the Mitsubishi MF355C / F family. Modern replacement belts are 54 mm × 1 mm flat rubber.
* Aluminium electrolytic capacitors on the drive logic board age and leak; if the drive becomes unreliable, recap the drive logic board with 105 °C low-ESR equivalents. See [[IBM PS/2 Model 50 Capacitor Replacement Guide]].


== Hard Drive Maintenance ==
=== Error codes ===


* '''20 MB ST-506''' (8550-021): a Seagate ST-506-class drive on the IBM Fixed Disk Adapter/A MCA card. Famously slow (85 ms access) and prone to head stiction after long storage. If the drive does not spin up, gently rotate the drive case while powered off to free a stuck spindle for one boot; image the contents and replace the drive at the earliest opportunity.
IBM's Micro Channel error list gives:<ref name="hmm" />
* '''30 MB ST-506''' (8550-031): similar ST-506 class on the same controller, faster seek.
* '''60 MB ESDI''' (8550-061): Maxtor / Miniscribe / Western Digital ESDI drive on the '''IBM ESDI Fixed Disk Adapter/A'''. The drive connector is on the rear edge of the controller card — no separate ribbon. Same drive family and controller used on the Model 60 (70 MB) and Model 70 / 80 (60 / 70 / 115 MB).


For all PS/2 hard drives the BIOS-side configuration is held in CMOS and configured through SETUP from the Reference Diskette. After a drive change, run "Set Configuration" to update the CMOS.
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Codes 161–168 (IBM ''PS/2 Hardware Maintenance Manual'', p. 36)'''
! Code !! IBM action and FRU order
|-
| 161 || Battery; system board; bus adapter
|-
| 162 || Check that all devices are powered on and the enable/disable settings; if the configuration has changed, run Automatic Configuration. Then any device, battery
|-
| 163 || Set the date and time
|-
| 165, 167 || Set configuration and features; system board
|-
| 166 || Reseat all adapters; run Advanced Diagnostics
|-
| 168 || Run Advanced Diagnostics; not always a hardware fault
|}


== MCA Card Maintenance ==
IBM also notes that the time-of-day count is interrupt-driven and can drift with interrupt activity without any hardware fault; check the time in the Reference Diskette's Set Features menu.<ref name="hmm" />


Each MCA card has a unique ID number stored in the card itself. The Reference Diskette reads the ID, looks up the corresponding ADF (Adapter Definition File) and configures interrupts, DMA channels and memory addresses automatically. After any card change:
=== Power-on password ===


# Boot the Reference Diskette.
To clear a forgotten power-on password, switch off. If the battery and speaker assembly has pins, short pins 2 and 3; if it has none, put a meter lead into connector 1 and touch the other end to frame ground. Switch on with the short in place, and remove it after POST has finished. The password is then set again from the Reference Diskette's Set Features option.<ref name="m50hmr" /><ref name="atbsa" /> The cover lock is there to stop someone removing the battery to clear the password.<ref name="m50tr" />
# Select '''Set Configuration → Run Auto Configuration'''.
# If the ADF for the new card is missing, the diskette prompts for the option diskette. Insert it; Auto Configuration copies the ADF to the working Reference Diskette.
# Save and reboot.


Without Auto Configuration the system reports a '''165 card-ID-mismatch error''' at POST with the F1 prompt.
== Connector care ==


== Capacitor Health ==
* The keyboard and pointing-device sockets are both 6-pin mini-DIN. The keyboard socket has a small keyboard symbol on the back panel and the other is for the pointing device. The interface logic is the same for both.<ref name="m50hmr" />
* One fuse on the planar protects the system board, keyboard and pointing device: F1, 3 A 250 V, IBM FRU 72X8561.<ref name="m50hmr" /><ref name="at8550" /><ref name="hmm" /> For code 305, a keyboard voltage error, IBM's order is the keyboard port fuse, the keyboard cable and the system board.<ref name="aterr">[https://www.ardent-tool.com/trouble/ps2error.html "PS/2 Error Codes"], Ardent Tool of Capitalism, with the tables for [https://www.ardent-tool.com/trouble/error_04.html 300–999]. The warm-boot warning and code 305 (keyboard port fuse, keyboard cable, system board).</ref> IBM's current limits are 275 mA for the keyboard port and 300 mA for the auxiliary port.<ref name="m50tr" />
* The serial and parallel ports are 25-pin D connectors; the video connector is a 15-pin D.<ref name="at8550" />
* The Micro Channel cards plug directly into the planar. When refitting an adapter, put it back in the same slot: the stored configuration depends on the slot, and a card in a different slot needs Set Configuration run again.<ref name="m50hmr" />


Through-hole tantalum capacitors (typically 10 µF / 16 V marked "106 16V") on the planar +5 V and +12 V rails can fail short-circuit and pull the PSU into fold-back (Power Good not asserted within 150 ms). Full procedure: [[IBM PS/2 Model 50 Capacitor Replacement Guide]].
== Drive interface ==


Aluminium electrolytics in the 94 W PSU age and need replacement after 30+ years. Symptoms include sagging rails under load, audible whine, PSU refusing to start when warm.
The diskette controller connects through a single 40-pin connector on the planar. A bus adapter plugs into it and carries the signals and supply voltages for up to two 3.5-inch drives, so the drives have no separate power connector.<ref name="m50hmr" /> IBM's FRU for the Model 50 diskette bus adapter is 72X8524.<ref name="hmm" /> The fixed disk connects through its own adapter in slot J10, separate from the three expansion slots.<ref name="at8550" /><ref name="ann49" />


== Recommended Tools ==
== Diskette drives ==


* Philips #2 screwdriver.
* The Model 50 ships with a 1.44 MB drive, IBM FRU 64F0207. IBM's specification is 80 tracks at 135 tracks per inch, two heads, 500,000 bit/s in high-density mode, 6 ms track to track, 15 ms settle, 500 ms maximum motor start and 300 rpm ±1.5 %.<ref name="hmm" /><ref name="ann49" />
* Anti-static strap connected to chassis ground.
* A 1.44 MB drive has "1.44" on its eject button. It reads and writes 1 MB and 2 MB diskettes; a 720 KB drive cannot use 2 MB diskettes.<ref name="m50hmr" /> IBM's instruction is not to format a 1 MB diskette as 1.44 MB, or a 2 MB diskette as 720 KB.<ref name="ann49" />
* The drives are direct drive and have no belt; the Mitsubishi MF355C turns its spindle directly at 300 rpm.<ref name="mf355c">Mitsubishi Electric, ''3.5 inch Flexible Disk Drive Standard Specifications, MF355C'', UGD-0527A, February 1987. Hosted on this wiki as [[:File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf]]. Section 3: brushless DC direct-drive spindle motor at 300 rpm.</ref>
* A drive that reads nothing, or whose errors get worse as it warms, usually has failed capacitors on its board. See [[IBM PS/2 Model 50 Capacitor Replacement Guide]] and [[Floppy Drive Repair]].
 
== Fixed disk ==
 
{| class="wikitable styled-table" style="width:100%;"
|+'''Model 50 fixed disks'''
! Submodel !! Drive (IBM FRU) !! Connection !! Average access
|-
| 8550-021 || 20 MB, 72X8522 || ST-506 adapter in slot J10 || 80 ms
|-
| 8550-031 || 30 MB, 6128287 || Controller in the drive, on a passive riser || 39 ms
|-
| 8550-061 || 60 MB, 6128294 || Controller in the drive, on a passive riser || 27 ms
|}
 
Sources: IBM's parts list and announcements.<ref name="hmm" /><ref name="ann50z" /><ref name="qref50">IBM, [https://www.ardent-tool.com/qtechinfo/GJAN-43VM6G.html "IBM PS/2 (Model 50) – Technical specifications"], document GJAN-43VM6G (2000), mirrored at ardent-tool.com. The 20 MB drive's 80 ms access time.</ref> The adapters and risers are described on [[IBM PS/2 Model 50#Fixed disk|the Model 50 page]].
 
* Before moving the machine, park the heads with the Reference Diskette's "Move the computer" option.<ref name="m50hmr" />
* A drive of this age that has stood for years may not spin up because the heads have stuck to the platters. Peter Wendt describes power cycling, or unplugging the unit, shaking it vertically and turning it sharply clockwise a few times; he warns never to lift the front and drop it on the desk. If the drive starts, copy the data off at once.<ref name="atstiction">[https://www.ardent-tool.com/trouble/Problems.html "Known Problems – Experience, RETAIN Tips, ECAs"], Ardent Tool of Capitalism. Peter Wendt on hard-disk stiction; IBM retain tip H005662 on installing the 3270 Connection, Token-Ring and PC Network adapters in the 8550 and other Micro Channel models.</ref>
 
== Micro Channel cards ==
 
Configuration is held in CMOS and set from the Reference Diskette.<ref name="m50hmr" /> After fitting or moving a card:
 
# Switch on with the Reference Diskette already in the drive. Warm-booting it can give false errors and a false indication that a power-on password is set.<ref name="aterr" />
# Add the card's files from its option diskette with Copy an Option Diskette if they are not already there.<ref name="hmm" />
# Note the current settings with View Configuration, then run Automatic Configuration or change the settings by hand.<ref name="hmm" />
# Save the result with Backup Configuration.
 
IBM retain tip H005662 sets rules for the 3270 Connection, Token-Ring and PC Network adapters in the 8550: the 3270 Connection adapter goes in the lowest-numbered free slot and uses interrupt 2; the Token-Ring adapter goes in a higher slot on interrupt 10 or 11; the PC Network adapter goes higher still on interrupt 3. Back up the configuration afterwards, because Automatic Configuration resets these interrupts to their defaults.<ref name="atstiction" />
 
Some non-IBM video adapters drive the VGA signals instead of receiving them. Two adapters that both drive VGA damage each other.<ref name="atcommon60" />
 
== Capacitor health ==
 
Ardent Tool's photograph of the Model 50 planar shows dipped tantalum capacitors and no aluminium electrolytics; the surface-mount electrolytics that leak are on the diskette drive and fixed-disk boards. See [[IBM PS/2 Model 50 Capacitor Replacement Guide]].<ref name="at8550" />
 
== Recommended tools ==
 
* Screwdriver and anti-static wrist strap.
* IBM's snap tool (72X8547) or a plastic spudger.
* T10 security Torx bit, to open the supply.
* Digital multimeter.
* Digital multimeter.
* IPA + foam swabs.
* Isopropyl alcohol and foam swabs.
* Plastic crowbar / spudger for captive push-pin tabs.
* The Reference Diskette and the option diskettes for every fitted card.
* Reference Diskette + ADF diskettes for all fitted MCA cards.
* A spare 6 V battery, 72X8498 or an equivalent such as a CR-P2.
* Spare Dallas DS12887+ for RTC replacement.
 
* Soldering iron with fine tip + solder wick for RTC and capacitor work.
See [[Recommended Tools]].
* Drive belt (54 × 1 mm flat) for the Mitsubishi MF355C family.


== Related Pages ==
== Related pages ==


* [[IBM PS/2 Model 50]]
* [[IBM PS/2 Model 50]]
* [[IBM PS/2 Model 50 Troubleshooting Guide]]
* [[IBM PS/2 Model 50 Troubleshooting Guide]]
* [[IBM PS/2 Model 50 Capacitor Replacement Guide]]
* [[IBM PS/2 Model 50 Capacitor Replacement Guide]]
* [[IBM PS/2 Model 60 Maintenance Guide]] — tower sibling with related procedures
* [[IBM PS/2 Model 60 Maintenance Guide]]
* [[Recommended Tools]]
* [[Battery Refurbishment]]
* [[Floppy Drive Repair]]
* [[Hard Drive Maintenance and Repair]]


== References ==
== References ==


* [https://www.dosdays.co.uk/computers/IBM%20PS2%20Model%2050/ibm_ps2_model_50.php IBM PS/2 Model 50 — DOS Days]. Source for PSU rating, integrated VGA, SIMM-pinout proprietary nature, captive push-pin construction.
<references />
* [https://www.ardent-tool.com/qtechinfo/GJAN-43VM6G.html IBM PS/2 Model 50 — Ardent Tool Quick Reference] (IBM GJAN-43VM6G). Source for FRU breakdown.
* [https://www.ardent-tool.com/qtechinfo/GJAN-43VMLQ.html IBM PS/2 Model 50 Z — Ardent Tool Quick Reference]. Source for Z-specific differences.
* [https://www.ardent-tool.com/trouble/ps2error.html PS/2 Error Codes], Ardent Tool. Reference for the 161/162/163 cluster and 165 card-ID-mismatch handling.
* IBM, ''IBM Personal System/2 Hardware Maintenance Manual'' (S52G-9971-02, October 1994). FRU listings and ECA recall data.


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Latest revision as of 20:51, 30 September 2026

A Model 50 Z with the cover removed, showing the planar, the drive structure and the drive riser card. (Image: Ruben de Rijcke, CC BY-SA 4.0, via Wikimedia Commons)

Routine maintenance on the IBM PS/2 Model 50 (machine type 8550) covers the original 8550-021 of April 1987 and the Model 50 Z (8550-031 and -061) of June 1988. All three are low desktop units: the planar lies on the floor of the chassis, the drives sit in a plastic structure over it, and the power supply slides onto an edge connector on the planar.[1]

Safety

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The 94 W supply rectifies the mains, and its primary reservoir capacitor holds a lethal charge after the machine is unplugged. Before working inside the supply, discharge that capacitor through a resistor and check with a meter that it has fallen to a few volts. The supply selects its input range automatically, so there is no voltage switch to set.[2]

There is no CRT in the system unit. IBM's 8503, 8512, 8513 and 8514 displays have their own tube and supply; see CRT Discharge Procedure.

Identifying your model

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The machine type and submodel are on the rear label, for example "Type 8550-061".

Model 50 and Model 50 Z
Model 50 (8550-021) Model 50 Z (8550-031, -061)
Announced 2 April 1987 2 June 1988
System board Type 1; FRU 72X8516 Type 2; FRU 10G4005
Wait states One None with 85 ns memory
Memory sockets Two 30-pin, with two 512 KB modules (FRU 72X8517) One 72-pin, with a 1 MB module (FRU 90X8624) or 2 MB (FRU 92F0104)
BIOS Four 27256 EPROMs Two 27512 EPROMs
Clock chip MC146818A at ZM47 MC146818A at ZM8
Fixed disk 20 MB ST-506 on an adapter 30 MB or 60 MB with integrated controller on a riser

Sources: the announcements, IBM's Technical Reference and parts list, and Ardent Tool's planar maps.[3][4][5][6][7][8]

Opening the system unit

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Tools: a screwdriver and an anti-static wrist strap. IBM supplied a snap tool, part 72X8547, for lifting the plastic snaps inside; it is stored in the system unit in front of the battery and speaker assembly.[2]

  1. Switch off and unplug everything.
  2. Unlock the cover lock if one is fitted.[2]
  3. Loosen the two cover screws at the rear. They are captive: when they turn freely they are undone.
  4. Slide the cover forward about two inches and lift it off.[1]

To refit the cover, place it on the base about an inch back from its final position so that it engages the guide at the bottom rear of the case, then slide it forward. If the diskette drive stops it lining up with the bezel, check that the drive is fully seated on its shelf.[1]

If the cover is locked and the key is lost, Peter Wendt's method is to undo the rear thumbscrews, push the cover forward as far as it goes, and lever a gap of 4–5 mm between the cover and the rear wall with a large flat screwdriver so the cover slides over the locking tab.[1] IBM's own answer is a new cover-lock assembly, which comes with two keys; one of the new keys and a pair of pliers are used to force the old lock.[2]

Taking the planar out

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Remove the adapter cards, diskette drive, fixed disk and drive riser card, then the fixed-disk adapter and the exhaust fan. Lift all the white plastic snaps, including the one under the speaker assembly, and pull the drive structure straight up. Remove the power supply, the three planar screws and the three screws holding the EMC shield over the rear ports. A 1/8-inch pin in the base locates the planar through a hole beside inductor LN2, so lift the planar straight up without tilting it.[1]

Cleaning

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  • Brush and blow dust off the planar, cards, drive structure and fan with low-pressure air. Hold the fan still while doing so.
  • The Model 50 supply has no fan of its own and a screen across its underside. Ardent Tool's advice is to clear the lint from that screen.[9]
  • PS/2 diskette drives have no shutter over the slot and collect dust. Ardent Tool's contributors report dirt on the Mitsubishi head actuator spindle and loose head-damper pads on ALPS drives.[10][11]
  • On the Models 60 and 80, dust under the supply fan over the keyboard controller, clock chip, diskette controller and serial controller has caused lost configuration, a wrong clock and disk errors that a new battery did not cure.[10][11] The same chips are on the Model 50 planar, so clean that area too.

Power supply checks

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The supply is an ASTEC AA13621, IBM P/N 90X9527, FRU 90X9366, rated 94 W.[9][6] Its outputs are +5 V, +12 V and −12 V; there is no −5 V output.[5]

After the machine has been off for ten seconds or more, the supply raises Power Good at switch-on, once every output is above its minimum under-voltage sense level. Power Good lights the green lamp on the front; if the lamp stays off, the supply is not working properly.[2]

Model 50 under-voltage sense levels
Output Sense level
+5 V +4.5 V
+12 V +10.8 V
−12 V −10.2 V

A short on any output, or an internal overvoltage fault before any output reaches 130 % of nominal, latches all outputs off. The supply only restarts once the fault has gone and the switch has been off for at least ten seconds.[5] A machine that starts and immediately shuts down is therefore as likely to have a short on the planar or a card as a faulty supply.

To test the supply itself, Ardent Tool's procedure is to remove it, place it connector-up, switch it on and measure at the 50-pin connector with the negative lead on pin 2:[9]

Model 50 supply test (supply removed)
Output + lead Minimum Maximum
−12 V Pin 1 −9.0 V −15.0 V
+12 V Pin 3 +9.0 V +15.0 V
+5 V Pin 15 +3.7 V +6.2 V

IBM's 1994 Hardware Maintenance Manual prints this table for the Models 50 and 70 with minimums of +15.0 V for +12 V and +6.2 V for +5 V, which are misprints.[6] If the voltages are wrong, check the power cord, which can make poor contact in the supply's socket, and then replace the supply. A supply with no output at all may have blown fuse F1 or F2.[9]

The connector carries −12 V on pin 1, +12 V on odd pins 3 to 13, +5 V on odd pins 15 to 47, ground on even pins 2 to 48, System Status on pin 49 and Power Good on pin 50.[9] The Model 60 supply does not fit: it uses a 15-pin planar connector and separate drive power cables.[12]

The fan is a separate assembly on the planar (J9 on the Model 50, J8 on the 50 Z). Ardent Tool reports Panaflo FBH-09A12L (12 V, 0.14 A) and Nidec D09B-12PLL (12 V, 0.09 A) fans; IBM's FRU is 72X8515.[9][7][8][6] Peter Wendt warns that the 94 W supply struggles once a processor upgrade, a lot of memory, a SCSI adapter and a high-resolution graphics card are fitted.[9]

Battery and clock

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The clock is a Motorola MC146818A soldered to the planar (ZM47 on the Model 50, ZM8 on the 50 Z). It is powered, when the machine is off, by a 6 V lithium battery in the battery and speaker assembly at the front of the chassis.[7][8][13] The CMOS RAM holds 64 bytes: 50 for configuration and security information, and 14 used by the clock for the date, time and battery level.[2]

IBM's FRU numbers are 33F5950 for the battery and speaker assembly and 72X8498 for the battery.[6] The battery is a two-cell 6 V lithium pack; Ardent Tool lists the CR-P2, DL223A, EL223AP, K223LA and PC223 camera batteries as equivalents.[14]

Testing the battery

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IBM retain tip H024809, which Ardent Tool reproduces for the Models 60, 65 SX and 80, covers the same battery (72X8498) and battery and speaker assembly (33F5950) that the Model 50 uses. It says that low battery voltage or a faulty assembly can cause intermittent 161, 162 and 163 errors, and gives this check:[10][6]

  1. Switch the system off.
  2. Remove the battery from the battery and speaker assembly. Measured in the assembly, the reading is not accurate.
  3. Set the meter to the 12 V DC range.
  4. Replace the battery if it reads below 5.5 V DC.

Alfred Arnold, quoted by Ardent Tool, notes that as the battery fails the clock's 32 kHz oscillator usually stops before the CMOS contents are lost. A machine that powers up showing the time at which it was switched off, with no 161 or 163 yet, has a battery near the end of its life.[10]

Replacing the battery

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IBM's caution: the lithium battery presents a fire, explosion or severe burn risk. Do not recharge it, disassemble it, heat it above 100 °C, burn it or expose its contents to water, and replace it only with part 72X8498. To avoid discharging the battery, take it out before disconnecting the assembly's cable, and connect the cable before fitting the battery.[2]

To remove the assembly on the Model 50 and 50 Z, press in the retaining clip at the bottom of the assembly (above the orange crystal holder) and push or pull the assembly up, away from the base. On the Model 50 the assembly is also held by its card-edge connector on the planar; the 50 Z uses a 6-pin header. The battery's contacts face the rear, against the spring clips.[15] Avoid pulling the battery cable off the planar while working elsewhere in the machine, which loses the configuration.[10]

After replacing the battery, start from the Reference Diskette. Run Automatic Configuration if the machine used default settings, or restore a customised configuration from the backup copy of the Reference Diskette.[2] IBM warns that Automatic Configuration can overwrite customised settings, so note them with View Configuration first.[6]

Error codes

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IBM's Micro Channel error list gives:[6]

Codes 161–168 (IBM PS/2 Hardware Maintenance Manual, p. 36)
Code IBM action and FRU order
161 Battery; system board; bus adapter
162 Check that all devices are powered on and the enable/disable settings; if the configuration has changed, run Automatic Configuration. Then any device, battery
163 Set the date and time
165, 167 Set configuration and features; system board
166 Reseat all adapters; run Advanced Diagnostics
168 Run Advanced Diagnostics; not always a hardware fault

IBM also notes that the time-of-day count is interrupt-driven and can drift with interrupt activity without any hardware fault; check the time in the Reference Diskette's Set Features menu.[6]

Power-on password

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To clear a forgotten power-on password, switch off. If the battery and speaker assembly has pins, short pins 2 and 3; if it has none, put a meter lead into connector 1 and touch the other end to frame ground. Switch on with the short in place, and remove it after POST has finished. The password is then set again from the Reference Diskette's Set Features option.[2][15] The cover lock is there to stop someone removing the battery to clear the password.[13]

Connector care

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  • The keyboard and pointing-device sockets are both 6-pin mini-DIN. The keyboard socket has a small keyboard symbol on the back panel and the other is for the pointing device. The interface logic is the same for both.[2]
  • One fuse on the planar protects the system board, keyboard and pointing device: F1, 3 A 250 V, IBM FRU 72X8561.[2][7][6] For code 305, a keyboard voltage error, IBM's order is the keyboard port fuse, the keyboard cable and the system board.[16] IBM's current limits are 275 mA for the keyboard port and 300 mA for the auxiliary port.[13]
  • The serial and parallel ports are 25-pin D connectors; the video connector is a 15-pin D.[7]
  • The Micro Channel cards plug directly into the planar. When refitting an adapter, put it back in the same slot: the stored configuration depends on the slot, and a card in a different slot needs Set Configuration run again.[2]

Drive interface

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The diskette controller connects through a single 40-pin connector on the planar. A bus adapter plugs into it and carries the signals and supply voltages for up to two 3.5-inch drives, so the drives have no separate power connector.[2] IBM's FRU for the Model 50 diskette bus adapter is 72X8524.[6] The fixed disk connects through its own adapter in slot J10, separate from the three expansion slots.[7][3]

Diskette drives

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  • The Model 50 ships with a 1.44 MB drive, IBM FRU 64F0207. IBM's specification is 80 tracks at 135 tracks per inch, two heads, 500,000 bit/s in high-density mode, 6 ms track to track, 15 ms settle, 500 ms maximum motor start and 300 rpm ±1.5 %.[6][3]
  • A 1.44 MB drive has "1.44" on its eject button. It reads and writes 1 MB and 2 MB diskettes; a 720 KB drive cannot use 2 MB diskettes.[2] IBM's instruction is not to format a 1 MB diskette as 1.44 MB, or a 2 MB diskette as 720 KB.[3]
  • The drives are direct drive and have no belt; the Mitsubishi MF355C turns its spindle directly at 300 rpm.[17]
  • A drive that reads nothing, or whose errors get worse as it warms, usually has failed capacitors on its board. See IBM PS/2 Model 50 Capacitor Replacement Guide and Floppy Drive Repair.

Fixed disk

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Model 50 fixed disks
Submodel Drive (IBM FRU) Connection Average access
8550-021 20 MB, 72X8522 ST-506 adapter in slot J10 80 ms
8550-031 30 MB, 6128287 Controller in the drive, on a passive riser 39 ms
8550-061 60 MB, 6128294 Controller in the drive, on a passive riser 27 ms

Sources: IBM's parts list and announcements.[6][4][18] The adapters and risers are described on the Model 50 page.

  • Before moving the machine, park the heads with the Reference Diskette's "Move the computer" option.[2]
  • A drive of this age that has stood for years may not spin up because the heads have stuck to the platters. Peter Wendt describes power cycling, or unplugging the unit, shaking it vertically and turning it sharply clockwise a few times; he warns never to lift the front and drop it on the desk. If the drive starts, copy the data off at once.[19]

Micro Channel cards

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Configuration is held in CMOS and set from the Reference Diskette.[2] After fitting or moving a card:

  1. Switch on with the Reference Diskette already in the drive. Warm-booting it can give false errors and a false indication that a power-on password is set.[16]
  2. Add the card's files from its option diskette with Copy an Option Diskette if they are not already there.[6]
  3. Note the current settings with View Configuration, then run Automatic Configuration or change the settings by hand.[6]
  4. Save the result with Backup Configuration.

IBM retain tip H005662 sets rules for the 3270 Connection, Token-Ring and PC Network adapters in the 8550: the 3270 Connection adapter goes in the lowest-numbered free slot and uses interrupt 2; the Token-Ring adapter goes in a higher slot on interrupt 10 or 11; the PC Network adapter goes higher still on interrupt 3. Back up the configuration afterwards, because Automatic Configuration resets these interrupts to their defaults.[19]

Some non-IBM video adapters drive the VGA signals instead of receiving them. Two adapters that both drive VGA damage each other.[10]

Capacitor health

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Ardent Tool's photograph of the Model 50 planar shows dipped tantalum capacitors and no aluminium electrolytics; the surface-mount electrolytics that leak are on the diskette drive and fixed-disk boards. See IBM PS/2 Model 50 Capacitor Replacement Guide.[7]

[edit | edit source]
  • Screwdriver and anti-static wrist strap.
  • IBM's snap tool (72X8547) or a plastic spudger.
  • T10 security Torx bit, to open the supply.
  • Digital multimeter.
  • Isopropyl alcohol and foam swabs.
  • The Reference Diskette and the option diskettes for every fitted card.
  • A spare 6 V battery, 72X8498 or an equivalent such as a CR-P2.

See Recommended Tools.

[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 "8550 and 8570 – Common Devices", Ardent Tool of Capitalism. Opening the case ("slide the case forward about two inches then lift up"), Peter Wendt's method for a locked case, closing the case, and removing the planar (drive-structure removal tool under the battery/speaker assembly, three planar screws, three EMC shield screws, 1/8-inch centring pin beside inductor LN2).
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 IBM, IBM PS/2 Model 50 Hardware Maintenance Reference, S64F-3989-00, March 1990. Hosted on this wiki as IBM PS2 Model 50 Hardware Maintenance Reference (PDF). Sections 1.1.1 (cover lock), 1.1.2 (power-on password), 1.2.2 (CMOS RAM), 1.2.7 (diskette-drive controller and bus adapter), 1.2.8 (keyboard and pointing-device connectors and fuse), 2.1 (diskette drive identification and media compatibility), 2.2 (Move the computer to park the heads), 3.1 (power supply, sense levels and the green power-good light), 4.0 (specifications), 5.0 (snap tool 72X8547), 6.2 (1010 battery and speaker assembly: caution and warning), 6.4 (1020 adapters: refit in the same slot).
  3. ↑ 3.0 3.1 3.2 3.3 IBM Announcement Letter 187-049, IBM Personal System/2 Model 50, 2 April 1987, text at ardent-tool.com. The 8550-021; 94 W automatic voltage-sensing supply; four 16-bit slots with one used by the disk controller; the 1.44 MB drive specification and IBM's instruction not to format a 1 MB diskette as 1.44 MB or a 2 MB diskette as 720 KB.
  4. ↑ 4.0 4.1 IBM Announcement Letter 188-080, IBM Personal System/2 Model 50 Z Desktop Systems with Improved Hardfile and Memory, 2 June 1988, text at ardent-tool.com. The 8550-031 and -061; zero wait states with 85 ns memory; 30 MB and 60 MB drives with the controller integrated, 39 ms and 27 ms average access.
  5. ↑ 5.0 5.1 5.2 IBM, IBM Personal System/2 Model 50 Technical Reference, October 1990. Hosted on this wiki as IBM PS2 Model 50 Technical Reference (October 1990) (PDF). Type 1 and Type 2 system boards, p. 1-3; supply outputs and output protection, pp. 1-11 and 1-12; ROM and RAM subsystems and memory connectors, pp. 3-7 to 3-9.
  6. ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 6.12 6.13 6.14 IBM, IBM Personal System/2 Hardware Maintenance Manual, S52G-9971-02, October 1994. Hosted on this wiki as IBM Personal System 2 Hardware Maintenance Manual (S52G-9971-02, October 1994) (PDF). Micro Channel numeric error codes 160–170, with the lithium battery caution, p. 36; Models 50 and 70 power supply connector, p. 141; "Real-Time Clock Problems" and "Running Automatic Configuration", p. 150; Model 50 parts list, p. 240.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 Louis Ohland, Tomáš Slavotínek et al., "8550 Planar", Ardent Tool of Capitalism. Designator map of planars 90X9161 and 15F6969: F1 250 V 3 A fuse, J1 battery/speaker connector, J9 fan, J10 fixed-disk adapter slot, J11 slot with auxiliary video extension, J15 video, J16 parallel, J17 serial, J19 mouse, J20 keyboard, ZM47 MC146818A, ZM13–ZM16 BIOS in 27256 EPROMs; the Model 50/60 Reference Disk v1.08.
  8. ↑ 8.0 8.1 8.2 Louis Ohland, Tomáš Slavotínek et al., "8550 Z Planar", Ardent Tool of Capitalism. Designator map of planar FRU 90X9533: F1 3 A 250 V, J2 battery/speaker header, J8 case fan header, ZM8 MC146818A, ZM45 72-pin SIMM socket, BIOS in two 27512 EPROMs; Peter Wendt's method for opening a locked case.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 Louis Ohland, Tomáš Slavotínek et al., "8550 / 8570 / 756x – Power Supply", Ardent Tool of Capitalism. The 50-pin connector pinout; the test-voltage table (−12 V −9.0 to −15.0 V at pins 2 and 1; +12 V +9.0 to +15.0 V at pins 2 and 3; +5 V +3.7 to +6.2 V at pins 2 and 15), measured with the supply removed and switched on; the ASTEC AA13621 (IBM P/N 90X9527, FRU 90X9366), 94 W; the separate fan that blows out of the rear (Panaflo FBH-09A12L 12 V 0.14 A or Nidec D09B-12PLL 12 V 0.09 A); the lint screen and T10 security Torx screws; removal (two screws at the back, one at the front inner corner); F1 or F2 as the suspect in a supply with no output; Peter Wendt's remark that the 94 W supply is weaker than assumed once upgrades are fitted.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 "60, 65 SX, and 80 – Common Devices", Ardent Tool of Capitalism. IBM retain tip H024809 on low battery voltage (battery 72X8498 in speaker/battery assembly 33F5950: remove it from the assembly, measure on the 12 V DC range, replace below 5.5 V DC; intermittent 161, 162 and 163 errors); Alfred Arnold on the clock stopping before the CMOS contents are lost; dust under the supply fan on the Models 60 and 80 causing lost configuration and disk errors; Peter Wendt on ALPS and Mitsubishi diskette drives; the warning that two adapters driving VGA signals damage each other.
  11. ↑ 11.0 11.1 "8580 Diskette Drives", Ardent Tool of Capitalism, content by Fred Spencer and Al Savage. The diskette controller under the supply fan collecting dirt that leaks current between pins and gives 6xx errors; Peter Wendt on mechanical causes of a 162; Al Savage's drive recap.
  12. ↑ "60, 65 SX, and 80 – Power Supply", Ardent Tool of Capitalism. The 15-pin planar power connector of the Models 60, 65 SX and 80, and their four-pin drive power cables.
  13. ↑ 13.0 13.1 13.2 IBM, IBM Personal System/2 Model 50 Technical Reference, May 1988. Hosted on this wiki as IBM PS2 Model 50 Technical Reference (May 1988) (PDF). Figure 1-7, "Physical Specifications", p. 1-9 (275 mA keyboard and 300 mA auxiliary port limits); "Real-Time Clock/Complementary Metal-Oxide Semiconductor RAM", p. 3-12 (6 V lithium battery; the cover lock prevents battery removal).
  14. ↑ Ardent Tool of Capitalism, "PS/2 RTC/CMOS Batteries", based on content by Bob Eager and Peter H. Wendt. Models 50 and 50 Z: FRU 72X8498, a 6 V two-cell lithium pack in the battery/speaker assembly; equivalents CR-P2, DL223A, EL223AP, K223LA and PC223.
  15. ↑ 15.0 15.1 Ardent Tool of Capitalism, "Battery/Speaker Assembly". FRUs 33F5950 and 72X8498; battery orientation; clearing a power-on password on the Models 50, 60, 70 and 80; removing the assembly on the Models 50, 50 Z and 70; the card-edge (Model 50) and 6-pin header (Model 50 Z) pinouts.
  16. ↑ 16.0 16.1 "PS/2 Error Codes", Ardent Tool of Capitalism, with the tables for 300–999. The warm-boot warning and code 305 (keyboard port fuse, keyboard cable, system board).
  17. ↑ Mitsubishi Electric, 3.5 inch Flexible Disk Drive Standard Specifications, MF355C, UGD-0527A, February 1987. Hosted on this wiki as File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf. Section 3: brushless DC direct-drive spindle motor at 300 rpm.
  18. ↑ IBM, "IBM PS/2 (Model 50) – Technical specifications", document GJAN-43VM6G (2000), mirrored at ardent-tool.com. The 20 MB drive's 80 ms access time.
  19. ↑ 19.0 19.1 "Known Problems – Experience, RETAIN Tips, ECAs", Ardent Tool of Capitalism. Peter Wendt on hard-disk stiction; IBM retain tip H005662 on installing the 3270 Connection, Token-Ring and PC Network adapters in the 8550 and other Micro Channel models.


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