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Verification pass: removed unsourced PSU and adapter capacitor tables, the fabricated 54x1 mm floppy belt (MF355C is direct drive), the through-hole drive-board values and the 106 16V tantalum figure extrapolated from IBM 51xx boards; corrected the SMD-electrolytic story (8550/50Z planars use SMD tantalum, the drives are what leak); corrected the drive/adapter lineup and the 104xx codes; full <ref> citations to IBM TechRef/HMR/HMM and ardent-tool; {{Unverified data}} cleared
Add Model 50 Z interior photo and Al Savage's drive capacitor photo
 
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This guide covers capacitor diagnosis and replacement on the '''[[IBM PS/2 Model 50]]''' (machine type 8550) — the original 8550-021 and the Model 50 Z, 8550-031 and 8550-061. It covers the planar, the 94 W power supply, the diskette drive and the fixed-disk drives.
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[[File:IBM PS2 Model 50Z internals.jpg|thumb|right|360px|A Model 50 Z with the cover off, showing the planar, the drive structure and the drive riser card. (Image: Ruben de Rijcke, CC BY-SA 4.0, via Wikimedia Commons)]]
Capacitor work on the '''[[IBM PS/2 Model 50]]''' (machine type 8550), both the original 8550-021 and the Model 50 Z (8550-031 and -061), involves the planar, the 94 W power supply, the diskette drive and the fixed-disk drive boards. IBM's service documents for the Model 50 list parts at FRU level and give no capacitor values for any of them.<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]]). Models 50 and 70 power supply connector, p. 141; Model 50 parts list (power supply 90X9366, fan 72X8515, system boards 72X8516 and 10G4005, 1.44 MB drive 64F0207, drives 72X8522, 6128287 and 6128294, adapters 72X8505, 90X9571 and 90X9441), p. 240.</ref><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 3.1 (automatic input switching, under-voltage sense levels, the green power-good light) and 3.2 (one short beep after a successful POST).</ref> Read the value and voltage on each part before removing it.


== Safety Warning ==
== Safety ==


The 94 W supply is a mains-rectified switching supply. Its primary side sits at mains potential and its reservoir capacitors hold a charge that can kill after the machine is unplugged. Recapping it is a reasonable thing to do, but treat it as live-mains work:
The 94 W supply rectifies the mains. Its primary reservoir capacitor holds a lethal charge after the machine is unplugged.


# Power off and unplug the mains lead.
# Switch off and unplug the mains lead.
# Discharge the primary reservoir capacitor through a 1 kΩ / 5 W resistor across its terminals, then confirm with a meter that it reads near zero before touching anything.
# Discharge the reservoir capacitor through a resistor (for example 1 kΩ, 5 W) and check with a meter that it is near zero before touching the board.
# Work one-handed where practical, and do not probe a powered primary side unless you are using an isolation transformer.
# Do not probe a powered primary side without an isolation transformer.


There is no CRT in the system unit; the matching IBM 8503, 8512, 8513 and 8514 displays contain their own tube and supply and are serviced separately. See [[CRT Discharge Procedure]] if you are working on the display.
The supply selects its input range automatically; there is no voltage switch.<ref name="m50hmr" /> There is no CRT in the system unit. For an IBM 8503, 8512, 8513 or 8514 display, see [[CRT Discharge Procedure]].


The supply is universal and voltage-sensing — there is no voltage selector switch to set wrongly.<ref name="ann49">IBM Announcement Letter 187-049, "IBM Personal System/2 Model 50", 2 April 1987, reproduced at [https://www.ardent-tool.com/8550/187-049.txt ardent-tool.com]. Source for the 94-watt automatic voltage-sensing power supply, the four 16-bit I/O slots with one occupied by the disk controller, the 1 MB planar memory expandable to 7 MB, the battery-backed clock and the IBM specification of the 1.44 MB diskette drive (300 rpm ±1.5 %, 500 kbps, 80 tracks).</ref>
== Where the capacitors are ==


== What Actually Fails on a Model 50 ==
* On the planar, Ardent Tool's photograph of the Model 50 planar (P/N 90X9161) shows yellow dipped tantalum capacitors, such as C72, C79 and C116, and no aluminium electrolytics.<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 and a photograph of the component side of 90X9161.</ref>
* The power supply, an ASTEC AA13621 switching supply, has its own electrolytics and mains suppression capacitors.<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 out of the machine; the ASTEC AA13621 (IBM P/N 90X9527, FRU 90X9366), 94 W maximum continuous output; the separate case fan; T10 security Torx case screws (five on the side, two on the top); the removal procedure; the lint screen on the underside; and the note that F1 or F2 is the suspect in a supply with no output.</ref>
* The diskette drive board has surface-mount electrolytics that go open or high-ESR and leak. This is the commonest capacitor fault on PS/2 machines of this age.<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. Al Savage's recap of Mitsubishi MF355W-99M3 card-edge drives (P/N 90X6766, FRU 72X8523), with the capacitor values and positions marked on his photograph; the diskette controller dirt problem; Peter Wendt's causes of a 162 from a drive that fails its POST seek test.</ref><ref name="ibmfiles">[http://www.ibmfiles.com/pages/ps2capacitors.htm "PS/2 Surface Mount Capacitors"], ibmfiles.com (2016). Two surface-mount electrolytics on the Mitsubishi PS/2 drive board, replaced with 10 µF through-hole parts on the pads; corrosion on the capacitors of PS/2 DBA hard disks and the same repair.</ref>
* The 30 MB and 60 MB fixed disks of the 031 and 061 have their controller built in.<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 30 MB and 60 MB drives, with "The fixed disk controller is integrated with the drive".</ref> The capacitors on PS/2 drives of this kind have been found corroding.<ref name="ibmfiles" />


This is worth stating plainly, because the Model 50 is often lumped in with the PS/2 models that suffer surface-mount electrolyte leakage.
== Planar ==


* '''The planar does not carry surface-mount aluminium electrolytic capacitors.''' Photographs of both the Model 50 planar (P/N 90X9161 / 15F6969) and the Model 50 Z planar (FRU 90X9533) show surface-mount tantalum chip capacitors and ceramics for supply-rail decoupling. There is no equivalent on these boards of the leaking aluminium cans found on the P70/P75 video board and planar.<ref name="at8550">[https://www.ardent-tool.com/8550/Planar.html 8550 Planar], Ardent Tool of Capitalism. Component-designator map for the Model 50 planar (P/N 90X9161 and 15F6969), including F1, the battery/speaker connector, the MC146818A RTC at ZM47 and the slot layout.</ref><ref name="at8550z">[https://www.ardent-tool.com/8550/Planar_Z.html 8550 Z Planar], Ardent Tool of Capitalism. Component-designator map for the Model 50 Z planar (FRU 90X9533), including F1, the battery/speaker header, the MC146818A RTC at ZM8, the single 72-pin SIMM socket and the 85 ns zero-wait-state memory.</ref><ref name="atp75">[https://www.ardent-tool.com/8573/P75_Caps.html 8573 P75 Failing Capacitors], Ardent Tool of Capitalism. Jim Shorney and Peter Wendt on the behaviour of leaking PS/2 surface-mount electrolytics: discoloured, grey or rough solder joints next to the can, joints that will not reflow because the electrolyte has contaminated them, and legs that pull free before the solder melts.</ref>
A shorted tantalum pulls its rail down. The supply only raises Power Good, and lights the green lamp on the front, once every rail is above its minimum under-voltage sense level (+4.5 V, +10.8 V, −10.2 V).<ref name="m50hmr" /> A short on any output latches the supply off until the fault is cleared and the switch has been off for ten seconds.<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]]). "Output Protection", p. 1-12.</ref>
* '''The diskette drive does.''' The documented, repeatable electrolyte problem on PS/2 machines of this era is in the 3.5-inch drive's own logic board, where surface-mount aluminium electrolytics go open-circuit or high-ESR and leak onto the pads.<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. Source for the PS/2 diskette drive part numbers (P/N 90X6766, FRU 72X8523 for the card-edge drives), for Al Savage's finding that the failing parts are surface-mount electrolytics that go open-circuit or high-ESR, for the diskette-controller dirt problem and for Peter Wendt's list of mechanical causes of a 162 at POST.</ref><ref name="ibmfiles">[https://www.ibmfiles.com/pages/ps2capacitors.htm PS/2 Surface Mount Capacitors], ibmfiles.com. Community teardown source; documents surface-mount electrolytic failure and pad corrosion on PS/2 Mitsubishi diskette drives and on the DBA hard-disk logic boards, and the through-hole-on-SMD-pad replacement technique.</ref>
* '''The fixed-disk logic boards do.''' The integrated drive-plus-controller ("DBA") drives fitted to the 8550-031 and 8550-061 carry the same style of surface-mount electrolytic, and corrosion around their pads has been documented.<ref name="ibmfiles" />
* '''The power supply is a normal 1980s switcher''' and ages like one, but IBM published no component-level data for it.


'''IBM never published capacitor values for any part of this machine.''' No parts list, technical reference, hardware maintenance reference or schematic set gives a capacitance or a working voltage for a planar, adapter or power-supply capacitor: IBM serviced these at FRU level and replaced whole assemblies.<ref name="hmm">IBM, ''IBM Personal System/2 Hardware Maintenance Manual'', S52G-9971-02, October 1994 — hosted on this wiki as [[:File:IBM PS2 HMM S52G-9971 Oct 1994.pdf]]. Sections "Power Supply Voltage Check", "System-Unit Power Supplies", "Numeric Error Codes" and the Model 50 / Model 60, 65, 80 parts catalogues.</ref><ref name="m50hmr">IBM, ''IBM PS/2 Model 50 Hardware Maintenance Reference'', part number 64F3989, form number S64F-3989-00, March 1990 — hosted on this wiki as [[:File:IBM PS2 Model 50 HMR.pdf]]. Sections 1.2.2 "CMOS RAM", 1.2.7 "Diskette-Drive Controller", 1.2.8 "Keyboard Connector and Pointing-Device Connector", 3.1 "Power Supply" and 3.2 "Power-On Self-Test".</ref><ref name="m50tr">IBM, ''IBM Personal System/2 Model 50 Technical Reference'', May 1988 — hosted on this wiki as [[:File:IBM PS2 Model 50 Technical Reference May88.pdf]]. Figure 1-2 "System Board Devices and Features", Figure 1-7 "Physical Specifications" and Section 3 "Real-Time Clock/CMOS RAM".</ref> Any table of "Model 50 capacitor values" you find elsewhere is therefore somebody's reading of a particular board, not a manufacturer specification. Read the values off your own board before ordering parts.
=== Taking the planar out ===


== Planar Capacitors ==
Ardent Tool's procedure for the Model 50 and 70:<ref name="atcommon50">[https://www.ardent-tool.com/50_70/Common.html "8550 and 8570 – Common Devices"], Ardent Tool of Capitalism. Opening the case, opening a locked unit, closing the case, and removing and refitting the planar, including the drive-structure removal tool under the battery/speaker assembly, the three planar screws, the EMC shield screws and the 1/8-inch centring pin beside inductor LN2.</ref>


[[File:IBM PS2 Model 50Z internals.jpg|thumb|right|400px|A Model 50 Z with the cover removed. The planar lies on the chassis floor, the drive structure sits over the front of it, and the drive riser card carries the diskette and fixed-disk connectors. The power supply slides on to an edge connector at the rear left.]]
# Remove all adapter cards, the diskette drive, the fixed disk and the drive riser card. On the Model 50, also remove the fixed-disk adapter and the exhaust fan.
 
# Find the drive-structure removal tool under the battery and speaker assembly. Use it to lift all the white plastic snaps, including the one under the speaker assembly, and pull the drive structure straight up.
The Model 50 and 50 Z planars use surface-mount tantalum chip capacitors (the amber or gold moulded blocks and beads visible across both boards) together with surface-mount ceramics. Tantalums fail short far more often than they fail open, and a shorted decoupling tantalum drags its rail down.<ref name="at8550" />
# Unscrew and remove the power supply.
 
# Remove the three screws holding the planar, and the three screws at the rear holding the EMC shield over the ports.
IBM did not mark these positions with values on the silkscreen, and no published designator-to-value map exists for either planar. Do not fit a replacement by reference to a value quoted for a different IBM machine — the widely-cited "10 µF / 16 V marked 106 16V" figure is documented for IBM 51xx (PC, XT, AT) motherboards, which use through-hole bead tantalums, and has never been shown to apply to a PS/2 planar.
# Lift the planar straight up. A 1/8-inch pin in the base locates it through a hole beside inductor LN2, and tilting the board levers against the pin.


=== Finding a shorted tantalum ===
=== Finding a shorted tantalum ===


# Unplug the machine and discharge the supply.
# Set a multimeter to its lowest resistance range or diode test.
# Remove the planar. Take out the adapter cards, the diskette drive, the fixed disk and the drive riser card; on the Model 50 also remove the fixed-disk adapter and the exhaust fan assembly. The drive-structure removal tool is stowed under the battery/speaker assembly and is used to lift the white plastic snaps holding the drive structure down — including the one hidden under the speaker. Three screws hold the planar itself, and a centring pin at the rear locates it, so lift the planar straight up rather than at an angle.<ref name="atcommon50">[https://www.ardent-tool.com/50_70/Common.html 8550 and 8570 — Common Devices], Ardent Tool of Capitalism. Source for the cover removal and locked-case procedures and for the planar removal sequence, including the drive-structure removal tool stowed under the battery/speaker assembly and the planar centring pin.</ref>
# Measure from ground to the positive side of each tantalum. A good part reads high after a brief charging pulse; a shorted one reads near 0 Ω.
# Set a multimeter to its lowest resistance range or to diode test and probe from ground to the rail side of each tantalum. A healthy part settles to a high reading after a brief charging pulse; a shorted one sits near 0 Ω.
# All parts on a rail are in parallel, so a low reading identifies a shorted rail. To find the part, lift one leg of the suspect capacitor and measure again.
# Everything on a given rail is in parallel, so a low reading points at a rail rather than at one part. Lift one end of the suspect capacitor and re-measure before condemning it.
# Replace it with a tantalum of the value printed on the old part and an equal or higher voltage, the right way round.
# Replace with an equivalent surface-mount tantalum or a low-ESR ceramic of the same value and equal or higher working voltage, read from the part you removed.


=== Removal and replacement ===
The "10 µF 16 V, marked 106 16V" figure that minuszerodegrees.net gives for IBM tantalums refers to 51xx (PC, XT and AT) boards, not the Model 50.<ref name="mzd">minuszerodegrees.net, [https://www.minuszerodegrees.net/failure/failure.htm "Commonly Failing Electronic Components (in vintage computers)"]. Tantalum failure modes and polarity; "On the IBM 51xx motherboards and cards, the tantalums used by IBM are commonly 10µF/16V"; line-suppression capacitor replacement rules; ruptured RIFA capacitors.</ref>


Leaking or failed surface-mount capacitors contaminate their own solder joints. Jim Shorney's account of PS/2 capacitor work is worth heeding: the joints often refuse to reflow, and the legs pull out of the contaminated solder before it melts. Work at a controlled temperature, add fresh leaded solder and flux to each joint first, and try to desolder rather than twist — but expect some parts to come away without the solder ever melting. Clean each pad and check it is still bonded to the board before fitting the new part.<ref name="atp75" />
== Power supply ==


Match polarity to the board. A tantalum fitted backwards will usually short on first power-up.
The Model 50 and 50 Z use the same supply, IBM FRU 90X9366, an ASTEC AA13621 rated 94 W maximum continuous output.<ref name="atpwr50" /><ref name="hmm" /> It has no fan of its own: the fan is a separate assembly on the planar.<ref name="atpwr50" /> IBM published no internal parts list or schematic for it, so record every value before removing parts.


== Power Supply (94 W) ==
# Discharge the reservoir capacitor and check it with a meter.
# Remove the supply: two screws at the back of the case and one at the front inner corner, then pull it off the planar edge connector.<ref name="atpwr50" />
# Open the case with a T10 security Torx bit (five screws on the side, two on the top).<ref name="atpwr50" />
# Photograph both sides of the board. Record each electrolytic's value, voltage, size and polarity.
# Fit 105 °C parts of the same capacitance and an equal or higher voltage, low-ESR where the original was.
# Replace a cracked or bulging suppression capacitor with one of the same capacitance, the same or higher AC voltage and the same safety class (X2 for X2, Y2 for Y2). An aged RIFA part ruptures with smoke and a strong odour.<ref name="mzd" />
# If the supply gave no output at all, check its fuses F1 and F2.<ref name="atpwr50" />
# Test it out of the machine before refitting.


The Model 50 and 50 Z share one supply: an ASTEC AA13621, IBM P/N 90X9527, IBM FRU P/N 90X9366, rated 94 W maximum continuous output.<ref name="atpwr50">[https://www.ardent-tool.com/50_70/Power.html 8550 / 8570 / 756x — Power Supply], Ardent Tool of Capitalism (Louis Ohland / Tomáš Slavotínek). Secondary source; it reproduces IBM's own power-supply connector pinout, test-voltage table and FRU data for the 8550. Source for the 50-pin edge-connector pinout, the ASTEC AA13621 identification, the 94 W rating, the security-Torx case fixings, the two internal fuses and the external fan part numbers.</ref><ref name="hmm" /> It is the same physical family as the Model 70 supply but with no built-in blower — on the Model 50 the fan is a separate assembly that plugs into the planar and exhausts through the rear panel.<ref name="atpwr50" />
=== Testing the supply ===


Opening it: the case is held by security Torx screws, five on the side and two on the top, and opens with a T10 security bit. There is no ultrasonic welding and no glue.<ref name="atpwr50" />
Ardent Tool's test, with the supply out of the machine and switched on, measures at the 50-pin connector with the negative lead on pin 2:<ref name="atpwr50" />


=== What is published, and what is not ===
{| class="wikitable styled-table" style="width:70%; text-align:center;"
 
|+'''Model 50 supply test (supply removed)'''
{| class="wikitable styled-table" style="width:100%;"
! Output !! + lead !! Minimum !! Maximum
|+'''Model 50 / 50 Z power supply — published data'''
! style="text-align:left;" | Item !! style="text-align:left;" | Value !! style="text-align:left;" | Source
|-
|-
| Rating || 94 W maximum continuous output || IBM announcement letter; IBM HMR
| −12 V || Pin 1 || −9.0 V || −15.0 V
|-
|-
| Input || 100–125 V or 200–240 V, automatically selected, 50/60 Hz || IBM HMR
| +12 V || Pin 3 || +9.0 V || +15.0 V
|-
|-
| Outputs || +5 V, +12 V, &minus;12 V (there is no &minus;5 V rail) || IBM HMM pinout
| +5 V || Pin 15 || +3.7 V || +6.2 V
|-
| Internal fuses || Two (F1, F2) — a dead supply with no outputs usually means one has blown || Ardent Tool
|-
| Capacitor values || '''Not published by IBM, and no reverse-engineered schematic of this unit is known to exist''' ||
|}
|}


Note the last row. The 94 W ASTEC unit has not been reverse-engineered and documented the way the tower supply has, so a recap means reading each can before you remove it. Photograph the board, write down every value and working voltage, and order to match.
IBM's 1994 ''Hardware Maintenance Manual'' prints the same table for the Models 50 and 70 with the +12 V minimum given as +15.0 V and the +5 V minimum as +6.2 V, which are misprints.<ref name="hmm" /> These are pass/fail limits for a supply out of the machine. In the machine, each output must stay above its under-voltage sense level or the supply withholds Power Good.<ref name="m50hmr" /> Pin 1 is −12 V, odd pins 3 to 13 are +12 V, odd pins 15 to 47 are +5 V, even pins 2 to 48 are ground, pin 49 is System Status and pin 50 is Power Good.<ref name="atpwr50" />


=== Recapping the 94 W supply ===
== Diskette drive board ==


# Discharge the primary reservoir capacitor and confirm with a meter.
IBM's 1994 FRU number for the Model 50's 1.44 MB drive is 64F0207.<ref name="hmm" /> PS/2 drives came from several makers, including Mitsubishi, ALPS and Sony, and their boards differ, so read the values on the board in front of you.<ref name="atfdd" /> Published repairs:
# Remove the supply: two screws at the back of the case, one screw at the front inner corner, then pull it off the planar edge connector.<ref name="atpwr50" />
# Open the case (T10 security Torx).
# Photograph the board from both sides before touching anything. Record each electrolytic's value, working voltage, diameter, lead spacing and polarity.
# Replace like for like: same capacitance, equal or higher working voltage, 105 °C rating, low-ESR parts on the secondary side where the originals were low-ESR types.
# Inspect the mains-side X- and Y-class suppression capacitors. These are safety-rated parts and must be replaced with equivalently rated X or Y class parts, never with ordinary film capacitors. Any RIFA-branded part showing crazing of the epoxy should be replaced on sight; they crack, absorb moisture and eventually vent.
# Check both fuses for continuity before reassembly.
# Reassemble and bench-test the outputs under a modest resistive load before refitting it to the machine. The connector is a 50-pin edge connector: pin 1 is &minus;12 V, odd pins 3–13 are +12 V, odd pins 15–47 are +5 V, even pins 2–48 are ground, pin 49 is System Status and pin 50 is Power Good.<ref name="atpwr50" />


IBM's own service limits, measured at the planar connector, are given on [[IBM PS/2 Model 50 Maintenance Guide|the maintenance page]]; a rebuilt supply that sits outside them has not been fixed.
{| class="wikitable styled-table" style="width:100%; text-align:left;"
 
|+'''Published PS/2 diskette drive recaps'''
== Diskette Drive Logic Board ==
! Drive !! Capacitors found !! Source
 
|-
This is the repair most Model 50s actually need.
| Mitsubishi MF355W-99M3, P/N 90X6766, FRU 72X8523 (card-edge) || Two 22 µF 16 V, one 1 µF 50 V and two 0.22 µF 50 V, open or high-ESR || Al Savage<ref name="atfdd" />
 
|-
PS/2 3.5-inch drives take power and signals through a single interface with no separate power connector, and were supplied by several manufacturers — Mitsubishi, ALPS, Sony and YE Data — under the same IBM part numbers (P/N 90X6766, FRU 72X8523 for the card-edge type used on the Model 50). The drives are physically different inside and most parts do not interchange, though they behave identically at the interface.<ref name="atfdd" />
| Mitsubishi PS/2 drive || Two surface-mount electrolytics, replaced with 10 µF through-hole parts || ibmfiles.com<ref name="ibmfiles" />
 
|-
Al Savage's teardown of failed PS/2 Mitsubishi drives found the cause to be surface-mount electrolytic capacitors on the drive's logic board that had gone open-circuit or very high-ESR. Replacing them recovered the drives. Reported values differ between drive revisions — one recap account names 22 µF, 1 µF and 0.22 µF parts, another replaced two capacitors with 10 µF — so '''read the values off your own board'''.<ref name="atfdd" /><ref name="atcommon60">[https://www.ardent-tool.com/60_65_80/Common.html 60, 65 SX, and 80 — Common Devices], Ardent Tool of Capitalism. Source for the side-cover and front-bezel removal, the dust-related configuration and disk faults under the power-supply fan, IBM retain tip H064300 (1780 on the 8560-041 and 8580-041), the ALPS/Mitsubishi diskette-drive comparison and the Mitsubishi "killer cap" note.</ref><ref name="ibmfiles" />
| ALPS PS/2 drive || One 4.7 µF 25 V, one 10 µF 16 V and three non-polarised 4.7 µF 16 V || Mac84<ref name="mac84">[https://mac84.net/web/repair-guides-documents/ibm-ps-2-floppy-disk-drive-recapping-guide-alps-drive/ "IBM PS/2 Floppy Disk Drive Recapping Guide (ALPS drive)"], Mac84. Values and positions on the ALPS drive board; the three 4.7 µF 16 V parts are non-polarised; the separate controller board is not covered.</ref>
 
|}
Symptoms that point at the drive's capacitors rather than its mechanics:


* Will not read any diskette, including known-good ones written elsewhere.
[[File:Mitsubishi MF355W-99M3 PS2 diskette drive capacitor locations.jpg|center|thumb|600px|Mitsubishi MF355W-99M3 drive board (FRU 72X8523) with the five failed surface-mount electrolytics marked. (Photo: Al Savage, via Ardent Tool of Capitalism)]]
* Intermittent read and write errors that worsen as the drive warms.
* A 6xx diskette error at POST. Mitsubishi drives in particular are noted for capacitors that produce 6xx electronic errors.<ref name="atcommon60" />
* Brown crust or discoloured, grey, rough solder joints around a can.


Symptoms that are '''not''' capacitor faults, and should be chased mechanically first:
Alan Douglas, quoted by Ardent Tool, used surface-mount electrolytics for the 22 µF and 1 µF positions and ceramics for the 0.22 µF ones, which are hard to find as electrolytics.<ref name="atcommon60">[https://www.ardent-tool.com/60_65_80/Common.html "60, 65 SX, and 80 – Common Devices"], Ardent Tool of Capitalism. Alan Douglas on replacing the 22 µF, 1 µF and 0.22 µF drive capacitors and on cutting the old parts in two to avoid tearing pads; Peter Wendt on ALPS and Mitsubishi drives (dust, head actuator dirt, the ALPS head-damper pad, Mitsubishi capacitors causing 6xx errors).</ref> Leaking surface-mount capacitors contaminate their joints. Jim Shorney found that the solder often will not melt and the legs pull out of it instead, with a risk of lifting the pad; Alan Douglas cut the old capacitors in two with flush cutters to reach the leads.<ref name="atp75">[https://www.ardent-tool.com/8573/P75_Caps.html "8573 P75 Failing Capacitors"], Ardent Tool of Capitalism. Jim Shorney on removing leaking PS/2 surface-mount electrolytics; discoloured, grey solder pads as a sign of leakage.</ref><ref name="atcommon60" /> Add fresh solder and flux first, and check each pad is still bonded before fitting the new part.


* A 162 at POST with the drive otherwise dead. During POST the heads are driven off track 0 and back within a fixed time; a sticking head carriage, a dirty track-0 photo-sensor or a detached head cushion will miss that window and the drive is thrown out of the configuration. The ALPS drives are known for losing the damper cushion glued to the head assembly; the Mitsubishi 355 collects dirt around the read/write head actuator spindle.<ref name="atfdd" /><ref name="atcommon60" />
Signs that point to the drive's capacitors:
* Speed or timing complaints blamed on a belt. '''There is no belt.''' The Mitsubishi MF355C specification states that the drive uses a DC brushless direct-drive motor coupled straight to the spindle at 300 rpm. Nothing in a PS/2 3.5-inch drive is belt-driven, and any guide that tells you to fit one is wrong.<ref name="mf355c">Mitsubishi Electric, ''3.5-inch Diskette Drive MF355C Specifications'', UGD-0527A, February 1987 — hosted on this wiki as [[:File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf]]. "The drive uses a DC brushless, direct-drive motor"; the spindle is directly coupled to the motor and rotates at 300 rpm. There is no belt in this drive.</ref>


Because the drive takes its supply through the interface, a drive fault can also be a supply fault — IBM lists the power supply among the FRUs for unclassified 6xx errors.<ref name="hmm" />
* the drive reads nothing, even known-good diskettes;
* read and write errors that get worse as the drive warms;
* 6xx errors at POST; Peter Wendt notes that Mitsubishi drives in particular have capacitors that cause them;<ref name="atcommon60" />
* brown residue or grey, discoloured solder around a capacitor.<ref name="atp75" />


== Fixed Disk Drives and Adapters ==
A 162 caused by the drive is usually mechanical. During POST the heads are stepped out from track 0 and back within a set time; a sticking head carriage, a dirty track-0 sensor or a loose head cushion makes the drive miss it, and it is dropped from the configuration.<ref name="atfdd" /> The drives are direct drive and have no belt.<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>


The Model 50 family uses three different arrangements, and they are not interchangeable:<ref name="athdd50">[https://www.ardent-tool.com/8550/HDD_Adapters.html 8550 HDD Adapters], Ardent Tool of Capitalism. Source for the three Model 50 drive adapters (the ST-506 adapters FRU 90X8070 and 90X8642, the bare DBA-ESDI riser FRU 90X9441 and the DBA-ESDI riser with BIOS FRU 90X9571), for the drive FRU numbers and for Peter Wendt's explanation that the desktop "ESDI" drives are integrated drive-plus-controller units rather than true ESDI.</ref>
== Fixed disks and adapters ==


{| class="wikitable styled-table" style="width:100%;"
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Model 50 fixed-disk arrangements'''
|+'''Model 50 fixed-disk arrangements'''
! style="text-align:left;" | Machine !! style="text-align:left;" | Drive !! style="text-align:left;" | Adapter
! Submodel !! Drive (IBM FRU) !! Adapter
|-
|-
| 8550-021 || 20 MB MFM / ST-506, FRU 72X8522 || ST-506 adapter in the dedicated adapter slot, FRU 90X8070 (early) or 90X8642 (later)
| 8550-021 || 20 MB ST-506, 72X8522 || ST-506 adapter in slot J10: FRU 72X8505 in IBM's 1994 list; Ardent Tool records 90X8070 (early) and 90X8642 (later)
|-
|-
| 8550-031 || 30 MB integrated drive-plus-controller, FRU 6128287 || Bare passive riser, FRU 90X9441
| 8550-031 || 30 MB with integrated controller, 6128287 || Passive riser
|-
|-
| 8550-061 || 60 MB integrated drive-plus-controller, FRU 6128294 || Bare passive riser, FRU 90X9441
| 8550-061 || 60 MB with integrated controller, 6128294 || Passive riser, FRU 90X9441
|-
|-
| 8550-021 with the 60 MB upgrade || 60 MB integrated drive-plus-controller || Riser carrying its own BIOS ROMs, FRU 90X9571
| 8550-021 with IBM's 60 MB upgrade || 60 MB with integrated controller || Riser with its own BIOS, FRU 90X9571
|}
|}


The units IBM's error codes call "ESDI" on the desktop machines are not true ESDI drives on a separate controller card. They are a hard disk and a Micro Channel controller built as one physical assembly, plugged into a riser that is mostly or entirely passive; the bare 90X9441 riser is an empty board that only routes signals. True ESDI controllers and separate ESDI drives belong to the towers — the Model 60 and Model 80.<ref name="athdd50" />
Sources: IBM's parts list and Ardent Tool.<ref name="hmm" /><ref name="athdd50">Louis Ohland, Tomáš Slavotínek ''et al.'', [https://www.ardent-tool.com/8550/HDD_Adapters.html "8550 HDD Adapters"], Ardent Tool of Capitalism. The ST-506 adapters FRU 90X8070 and 90X8642 for the 021; the bare riser FRU 90X9441, "completely empty otherwise", with a board variant 15F8434 that has silkscreen outlines for two capacitors that are not fitted; the riser with BIOS FRU 90X9571 for an 021 with the 60 MB upgrade; and Peter Wendt's explanation that the integrated drives combine a Micro Channel controller and disk in one unit.</ref>
 
The practical consequences for capacitor work:
 
* On the '''8550-031 and 8550-061''', the capacitors that matter are on the drive's own logic board, not on the riser. These are surface-mount electrolytics of the same family as the diskette-drive parts, and corrosion around their pads has been photographed on PS/2 DBA drives.<ref name="ibmfiles" /> Read the values from your board.
* On the '''bare 90X9441 riser''' there is nothing to recap: the board is a passive interconnect. One variant, circuit board 15F8434, carries unpopulated silkscreen outlines for two capacitors that IBM never fitted — do not read those as missing parts.<ref name="athdd50" />
* On the '''8550-021 ST-506 adapter''' and the '''90X9571 riser''', no published capacitor list exists. Inspect, and replace only what is visibly failed or measures bad.


If an integrated drive reports a 104xx error, note which one before reaching for a soldering iron: 010455 and 010456 are controller errors, 010462 a controller seek error, 010464 a drive read error, and 010483 points at the adapter and the system board — and, for older drives, at spindle stiction rather than electronics.<ref name="aterr">[https://www.ardent-tool.com/trouble/ps2error.html PS/2 Error Codes] and the linked code tables [https://www.ardent-tool.com/trouble/error_02.html 160–199], [https://www.ardent-tool.com/trouble/error_03.html 200–299], [https://www.ardent-tool.com/trouble/error_06.html 1500–2999] and [https://www.ardent-tool.com/trouble/error_08.html 10000–11999], Ardent Tool of Capitalism. Secondary source; the tables reproduce IBM's own symptom-to-FRU lists.</ref><ref name="atstiction">[https://www.ardent-tool.com/trouble/Problems.html Known Problems — Experience, RETAIN Tips, ECAs], Ardent Tool of Capitalism. Source for Peter Wendt's account of hard-disk stiction and the recovery options, and for IBM retain tip H005662, the adapter installation restrictions and configuration backup/restore caution for the 3270 Connection, Token-Ring and PC Network adapters in the 8550, 8555, 8560, 8565, 8570, 8580 and 9585.</ref> For the ST-506 machine, 1702 indicts the adapter specifically while the rest of the 17xx range points first at the drive, then the cable, then the adapter, the planar and the power supply.<ref name="aterr" /><ref name="hmm" />
* On the 031 and 061 the capacitors that matter are on the drive's own board. The ibmfiles.com repair fitted through-hole capacitors to the surface-mount pads, taking care not to shear the taller parts off.<ref name="ibmfiles" />
* The bare 90X9441 riser has no components to replace. One version of its board (15F8434) has outlines for two capacitors that IBM never fitted.<ref name="athdd50" />
* No capacitor list is published for the 021's ST-506 adapter or the 90X9571 riser. Replace only parts that are visibly damaged or measure bad.


== After a Recap ==
Before blaming capacitors on an integrated drive, read the error code. In Ardent Tool's copy of IBM's list, 10455 and 10456 are controller errors, 10462 a controller seek error and 10464 a read error, and for 10483 the FRUs are the adapter and the system board, with a pointer to stiction on older drives. For the 021's ST-506 drive, 1702 points to the adapter; most other 17xx codes point to the drive, cable, adapter, system board and power supply in that order.<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_06.html 1500–2999] (17xx, ST-506) and [https://www.ardent-tool.com/trouble/error_08.html 10000–11999] (104xx, integrated drives); the Advanced Diagnostics (Ctrl-A) instruction.</ref> See [[IBM PS/2 Model 50 Troubleshooting Guide]].


# Bench-test the supply on its own first, under load, against IBM's service limits.
== After the work ==
# Refit and start from the Reference Diskette rather than the hard disk.
# Run Automatic Configuration if any adapter changed, then run Advanced Diagnostics (from System Programs, press Ctrl-A at the main menu).<ref name="aterr" />
# A successful POST ends in one short beep.<ref name="m50hmr" />
# Leave the machine running a long memory test to shake out marginal decoupling.


If something fails immediately after a recap, check the polarity of every part you fitted before suspecting anything else.
# Test the supply on its own first, against the limits above.
# Refit it and start from the Reference Diskette. A successful POST ends with one short beep.<ref name="m50hmr" />
# Run Automatic Configuration if anything changed, then Advanced Diagnostics (Ctrl-A at the Reference Diskette main menu).<ref name="aterr" />
# Run the memory tests repeatedly to find marginal decoupling.


== When Not to Recap ==
If a fault appears after a recap, check the polarity of every part you fitted.


A Model 50 that starts reliably, POSTs clean, holds its configuration and reads and writes diskettes does not need its planar touched. Blanket-replacing surface-mount tantalums on a working board risks lifting pads for no gain.
== When not to recap ==


Do act if you see:
A Model 50 that starts reliably, passes POST, keeps its configuration and reads diskettes does not need its planar touched. Act when there is:


* Any fluid, crust or crystalline residue near a capacitor, or discoloured, grey or rough solder at its pads.<ref name="atp75" />
* fluid, crust or grey, discoloured solder at a capacitor;<ref name="atp75" />
* A rail outside IBM's service limits, or Power Good never asserting (the green front-panel light stays off).<ref name="m50hmr" />
* a supply output outside the limits above, or no Power Good (the green lamp stays off);<ref name="m50hmr" />
* Diskette read/write failures or 6xx errors on a mechanically sound drive.
* diskette errors on a drive that is mechanically sound;
* A supply that whines, smells, or will not start when warm.
* a supply that whines, smells or will not start when warm;
* A shorted decoupling capacitor confirmed out of circuit.
* a shorted capacitor confirmed out of circuit.


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


* [[IBM PS/2 Model 50]]
* [[IBM PS/2 Model 50]]
* [[IBM PS/2 Model 50 Maintenance Guide]]
* [[IBM PS/2 Model 50 Maintenance Guide]]
* [[IBM PS/2 Model 50 Troubleshooting Guide]]
* [[IBM PS/2 Model 50 Troubleshooting Guide]]
* [[IBM PS/2 Model 60 Capacitor Replacement Guide]] — the tower, which uses a different and better-documented power supply
* [[IBM PS/2 Model 60 Capacitor Replacement Guide]]
* [[Capacitor Failure Symptoms]]
* [[Capacitor Failure Symptoms]]
* [[Battery Explosion, Capacitor or Corrosion Damage]]
* [[Battery Explosion, Capacitor or Corrosion Damage]]

Latest revision as of 20:49, 30 September 2026

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

Capacitor work on the IBM PS/2 Model 50 (machine type 8550), both the original 8550-021 and the Model 50 Z (8550-031 and -061), involves the planar, the 94 W power supply, the diskette drive and the fixed-disk drive boards. IBM's service documents for the Model 50 list parts at FRU level and give no capacitor values for any of them.[1][2] Read the value and voltage on each part before removing it.

Safety

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The 94 W supply rectifies the mains. Its primary reservoir capacitor holds a lethal charge after the machine is unplugged.

  1. Switch off and unplug the mains lead.
  2. Discharge the reservoir capacitor through a resistor (for example 1 kΩ, 5 W) and check with a meter that it is near zero before touching the board.
  3. Do not probe a powered primary side without an isolation transformer.

The supply selects its input range automatically; there is no voltage switch.[2] There is no CRT in the system unit. For an IBM 8503, 8512, 8513 or 8514 display, see CRT Discharge Procedure.

Where the capacitors are

[edit | edit source]
  • On the planar, Ardent Tool's photograph of the Model 50 planar (P/N 90X9161) shows yellow dipped tantalum capacitors, such as C72, C79 and C116, and no aluminium electrolytics.[3]
  • The power supply, an ASTEC AA13621 switching supply, has its own electrolytics and mains suppression capacitors.[4]
  • The diskette drive board has surface-mount electrolytics that go open or high-ESR and leak. This is the commonest capacitor fault on PS/2 machines of this age.[5][6]
  • The 30 MB and 60 MB fixed disks of the 031 and 061 have their controller built in.[7] The capacitors on PS/2 drives of this kind have been found corroding.[6]

Planar

[edit | edit source]

A shorted tantalum pulls its rail down. The supply only raises Power Good, and lights the green lamp on the front, once every rail is above its minimum under-voltage sense level (+4.5 V, +10.8 V, −10.2 V).[2] A short on any output latches the supply off until the fault is cleared and the switch has been off for ten seconds.[8]

Taking the planar out

[edit | edit source]

Ardent Tool's procedure for the Model 50 and 70:[9]

  1. Remove all adapter cards, the diskette drive, the fixed disk and the drive riser card. On the Model 50, also remove the fixed-disk adapter and the exhaust fan.
  2. Find the drive-structure removal tool under the battery and speaker assembly. Use it to lift all the white plastic snaps, including the one under the speaker assembly, and pull the drive structure straight up.
  3. Unscrew and remove the power supply.
  4. Remove the three screws holding the planar, and the three screws at the rear holding the EMC shield over the ports.
  5. Lift the planar straight up. A 1/8-inch pin in the base locates it through a hole beside inductor LN2, and tilting the board levers against the pin.

Finding a shorted tantalum

[edit | edit source]
  1. Set a multimeter to its lowest resistance range or diode test.
  2. Measure from ground to the positive side of each tantalum. A good part reads high after a brief charging pulse; a shorted one reads near 0 Ω.
  3. All parts on a rail are in parallel, so a low reading identifies a shorted rail. To find the part, lift one leg of the suspect capacitor and measure again.
  4. Replace it with a tantalum of the value printed on the old part and an equal or higher voltage, the right way round.

The "10 µF 16 V, marked 106 16V" figure that minuszerodegrees.net gives for IBM tantalums refers to 51xx (PC, XT and AT) boards, not the Model 50.[10]

Power supply

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The Model 50 and 50 Z use the same supply, IBM FRU 90X9366, an ASTEC AA13621 rated 94 W maximum continuous output.[4][1] It has no fan of its own: the fan is a separate assembly on the planar.[4] IBM published no internal parts list or schematic for it, so record every value before removing parts.

  1. Discharge the reservoir capacitor and check it with a meter.
  2. Remove the supply: two screws at the back of the case and one at the front inner corner, then pull it off the planar edge connector.[4]
  3. Open the case with a T10 security Torx bit (five screws on the side, two on the top).[4]
  4. Photograph both sides of the board. Record each electrolytic's value, voltage, size and polarity.
  5. Fit 105 °C parts of the same capacitance and an equal or higher voltage, low-ESR where the original was.
  6. Replace a cracked or bulging suppression capacitor with one of the same capacitance, the same or higher AC voltage and the same safety class (X2 for X2, Y2 for Y2). An aged RIFA part ruptures with smoke and a strong odour.[10]
  7. If the supply gave no output at all, check its fuses F1 and F2.[4]
  8. Test it out of the machine before refitting.

Testing the supply

[edit | edit source]

Ardent Tool's test, with the supply out of the machine and switched on, measures at the 50-pin connector with the negative lead on pin 2:[4]

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 the same table for the Models 50 and 70 with the +12 V minimum given as +15.0 V and the +5 V minimum as +6.2 V, which are misprints.[1] These are pass/fail limits for a supply out of the machine. In the machine, each output must stay above its under-voltage sense level or the supply withholds Power Good.[2] Pin 1 is −12 V, odd pins 3 to 13 are +12 V, odd pins 15 to 47 are +5 V, even pins 2 to 48 are ground, pin 49 is System Status and pin 50 is Power Good.[4]

Diskette drive board

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IBM's 1994 FRU number for the Model 50's 1.44 MB drive is 64F0207.[1] PS/2 drives came from several makers, including Mitsubishi, ALPS and Sony, and their boards differ, so read the values on the board in front of you.[5] Published repairs:

Published PS/2 diskette drive recaps
Drive Capacitors found Source
Mitsubishi MF355W-99M3, P/N 90X6766, FRU 72X8523 (card-edge) Two 22 µF 16 V, one 1 µF 50 V and two 0.22 µF 50 V, open or high-ESR Al Savage[5]
Mitsubishi PS/2 drive Two surface-mount electrolytics, replaced with 10 µF through-hole parts ibmfiles.com[6]
ALPS PS/2 drive One 4.7 µF 25 V, one 10 µF 16 V and three non-polarised 4.7 µF 16 V Mac84[11]
Mitsubishi MF355W-99M3 drive board (FRU 72X8523) with the five failed surface-mount electrolytics marked. (Photo: Al Savage, via Ardent Tool of Capitalism)

Alan Douglas, quoted by Ardent Tool, used surface-mount electrolytics for the 22 µF and 1 µF positions and ceramics for the 0.22 µF ones, which are hard to find as electrolytics.[12] Leaking surface-mount capacitors contaminate their joints. Jim Shorney found that the solder often will not melt and the legs pull out of it instead, with a risk of lifting the pad; Alan Douglas cut the old capacitors in two with flush cutters to reach the leads.[13][12] Add fresh solder and flux first, and check each pad is still bonded before fitting the new part.

Signs that point to the drive's capacitors:

  • the drive reads nothing, even known-good diskettes;
  • read and write errors that get worse as the drive warms;
  • 6xx errors at POST; Peter Wendt notes that Mitsubishi drives in particular have capacitors that cause them;[12]
  • brown residue or grey, discoloured solder around a capacitor.[13]

A 162 caused by the drive is usually mechanical. During POST the heads are stepped out from track 0 and back within a set time; a sticking head carriage, a dirty track-0 sensor or a loose head cushion makes the drive miss it, and it is dropped from the configuration.[5] The drives are direct drive and have no belt.[14]

Fixed disks and adapters

[edit | edit source]
Model 50 fixed-disk arrangements
Submodel Drive (IBM FRU) Adapter
8550-021 20 MB ST-506, 72X8522 ST-506 adapter in slot J10: FRU 72X8505 in IBM's 1994 list; Ardent Tool records 90X8070 (early) and 90X8642 (later)
8550-031 30 MB with integrated controller, 6128287 Passive riser
8550-061 60 MB with integrated controller, 6128294 Passive riser, FRU 90X9441
8550-021 with IBM's 60 MB upgrade 60 MB with integrated controller Riser with its own BIOS, FRU 90X9571

Sources: IBM's parts list and Ardent Tool.[1][15]

  • On the 031 and 061 the capacitors that matter are on the drive's own board. The ibmfiles.com repair fitted through-hole capacitors to the surface-mount pads, taking care not to shear the taller parts off.[6]
  • The bare 90X9441 riser has no components to replace. One version of its board (15F8434) has outlines for two capacitors that IBM never fitted.[15]
  • No capacitor list is published for the 021's ST-506 adapter or the 90X9571 riser. Replace only parts that are visibly damaged or measure bad.

Before blaming capacitors on an integrated drive, read the error code. In Ardent Tool's copy of IBM's list, 10455 and 10456 are controller errors, 10462 a controller seek error and 10464 a read error, and for 10483 the FRUs are the adapter and the system board, with a pointer to stiction on older drives. For the 021's ST-506 drive, 1702 points to the adapter; most other 17xx codes point to the drive, cable, adapter, system board and power supply in that order.[16] See IBM PS/2 Model 50 Troubleshooting Guide.

After the work

[edit | edit source]
  1. Test the supply on its own first, against the limits above.
  2. Refit it and start from the Reference Diskette. A successful POST ends with one short beep.[2]
  3. Run Automatic Configuration if anything changed, then Advanced Diagnostics (Ctrl-A at the Reference Diskette main menu).[16]
  4. Run the memory tests repeatedly to find marginal decoupling.

If a fault appears after a recap, check the polarity of every part you fitted.

When not to recap

[edit | edit source]

A Model 50 that starts reliably, passes POST, keeps its configuration and reads diskettes does not need its planar touched. Act when there is:

  • fluid, crust or grey, discoloured solder at a capacitor;[13]
  • a supply output outside the limits above, or no Power Good (the green lamp stays off);[2]
  • diskette errors on a drive that is mechanically sound;
  • a supply that whines, smells or will not start when warm;
  • a shorted capacitor confirmed out of circuit.
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 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). Models 50 and 70 power supply connector, p. 141; Model 50 parts list (power supply 90X9366, fan 72X8515, system boards 72X8516 and 10G4005, 1.44 MB drive 64F0207, drives 72X8522, 6128287 and 6128294, adapters 72X8505, 90X9571 and 90X9441), p. 240.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 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 3.1 (automatic input switching, under-voltage sense levels, the green power-good light) and 3.2 (one short beep after a successful POST).
  3. ↑ Louis Ohland, Tomáš Slavotínek et al., "8550 Planar", Ardent Tool of Capitalism. Designator map of planars 90X9161 and 15F6969 and a photograph of the component side of 90X9161.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 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 out of the machine; the ASTEC AA13621 (IBM P/N 90X9527, FRU 90X9366), 94 W maximum continuous output; the separate case fan; T10 security Torx case screws (five on the side, two on the top); the removal procedure; the lint screen on the underside; and the note that F1 or F2 is the suspect in a supply with no output.
  5. ↑ 5.0 5.1 5.2 5.3 "8580 Diskette Drives", Ardent Tool of Capitalism, content by Fred Spencer and Al Savage. Al Savage's recap of Mitsubishi MF355W-99M3 card-edge drives (P/N 90X6766, FRU 72X8523), with the capacitor values and positions marked on his photograph; the diskette controller dirt problem; Peter Wendt's causes of a 162 from a drive that fails its POST seek test.
  6. ↑ 6.0 6.1 6.2 6.3 "PS/2 Surface Mount Capacitors", ibmfiles.com (2016). Two surface-mount electrolytics on the Mitsubishi PS/2 drive board, replaced with 10 µF through-hole parts on the pads; corrosion on the capacitors of PS/2 DBA hard disks and the same repair.
  7. ↑ 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 30 MB and 60 MB drives, with "The fixed disk controller is integrated with the drive".
  8. ↑ 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). "Output Protection", p. 1-12.
  9. ↑ "8550 and 8570 – Common Devices", Ardent Tool of Capitalism. Opening the case, opening a locked unit, closing the case, and removing and refitting the planar, including the drive-structure removal tool under the battery/speaker assembly, the three planar screws, the EMC shield screws and the 1/8-inch centring pin beside inductor LN2.
  10. ↑ 10.0 10.1 minuszerodegrees.net, "Commonly Failing Electronic Components (in vintage computers)". Tantalum failure modes and polarity; "On the IBM 51xx motherboards and cards, the tantalums used by IBM are commonly 10µF/16V"; line-suppression capacitor replacement rules; ruptured RIFA capacitors.
  11. ↑ "IBM PS/2 Floppy Disk Drive Recapping Guide (ALPS drive)", Mac84. Values and positions on the ALPS drive board; the three 4.7 µF 16 V parts are non-polarised; the separate controller board is not covered.
  12. ↑ 12.0 12.1 12.2 "60, 65 SX, and 80 – Common Devices", Ardent Tool of Capitalism. Alan Douglas on replacing the 22 µF, 1 µF and 0.22 µF drive capacitors and on cutting the old parts in two to avoid tearing pads; Peter Wendt on ALPS and Mitsubishi drives (dust, head actuator dirt, the ALPS head-damper pad, Mitsubishi capacitors causing 6xx errors).
  13. ↑ 13.0 13.1 13.2 "8573 P75 Failing Capacitors", Ardent Tool of Capitalism. Jim Shorney on removing leaking PS/2 surface-mount electrolytics; discoloured, grey solder pads as a sign of leakage.
  14. ↑ 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.
  15. ↑ 15.0 15.1 Louis Ohland, Tomáš Slavotínek et al., "8550 HDD Adapters", Ardent Tool of Capitalism. The ST-506 adapters FRU 90X8070 and 90X8642 for the 021; the bare riser FRU 90X9441, "completely empty otherwise", with a board variant 15F8434 that has silkscreen outlines for two capacitors that are not fitted; the riser with BIOS FRU 90X9571 for an 021 with the 60 MB upgrade; and Peter Wendt's explanation that the integrated drives combine a Micro Channel controller and disk in one unit.
  16. ↑ 16.0 16.1 "PS/2 Error Codes", Ardent Tool of Capitalism, with the tables for 1500–2999 (17xx, ST-506) and 10000–11999 (104xx, integrated drives); the Advanced Diagnostics (Ctrl-A) instruction.


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