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{{Infobox computer
{{Infobox computer
| name          = IBM Personal System/2 Model 50
| name          = IBM Personal System/2 Model 50
| logo          = [[File:IBM PS2 Model 50 badge.svg|150px]]
| image        = [[File:IBM PS2 Model 50 system.jpg|260px]]
| image        = [[File:IBM PS2 Model 50 system.jpg|260px]]
| caption      = IBM PS/2 Model 50 (8550-021) MCA 286 desktop
| caption      = IBM PS/2 Model 50 (8550)
| developer    = IBM Entry Systems Division, Boca Raton
| developer    = IBM Entry Systems Division, Boca Raton
| manufacturer  = IBM
| manufacturer  = IBM
| type          = Mid-range desktop personal computer
| type          = Mid-range desktop personal computer
| release date  = April 2, 1987 (Model 50); June 2, 1988 (Model 50 Z)
| release date  = 2 April 1987 (Model 50); June 1988 (Model 50 Z)
| discontinued  = Model 50 Z continued through c. 1992
| cpu          = Intel 80286 @ 10 MHz, 1 wait state (Model 50); 0 wait states (Model 50 Z)
| cpu          = Intel 80286 @ 10 MHz, 1 wait state (Model 50); 0 wait states (Model 50 Z)
| memory        = 1 MB on planar; 7 MB max via MCA memory cards
| memory        = 1 MB on the system board; 7 MB system maximum via channel memory
| storage      = 1.44 MB 3.5" diskette + 20 MB ST-506 (Model 50) or 30 MB ST-506 / 60 MB ESDI (Model 50 Z) via MCA controller
| storage      = 1.44 MB 3.5" diskette; 20 MB or 30 MB fixed disk on an ST-506 adapter, or 60 MB DBA drive on a riser
| display      = Integrated VGA on planar (15-pin DSUB)
| display      = VGA integrated on the system board, 256 KB video memory
| sound        = PC speaker
| sound        = PC speaker
| dimensions    = 360 W × 420 D × 140 H mm
| dimensions    = 360 mm W × 420 mm D × 140 mm H
| weight        = 9.55 kg (21 lb)
| weight        = 9.55 kg (21 lb)
| os            = IBM PC DOS 3.3 and later; IBM OS/2 1.x; IBM AIX PS/2
| os            = IBM PC DOS 3.3 and later; IBM OS/2 1.x; IBM AIX PS/2
| predecessor  = [[IBM PC AT (5170)]]
| predecessor  = [[IBM PC AT (5170)]]
| successor    = [[IBM PS/2 Model 70]] (Model 50 / 50 Z family)
| successor    = [[IBM PS/2 Model 70]]
| model        = 8550
| model        = 8550
}}
}}


The '''IBM Personal System/2 Model 50''' (machine type '''8550''') is the mid-range desktop in IBM's PS/2 family, announced on April 2, 1987 alongside the [[IBM PS/2 Model 30]], [[IBM PS/2 Model 60]] and [[IBM PS/2 Model 80]]. The Model 50 was the entry-level MCA + VGA PS/2; the lower-priced Model 30 used ISA + MCGA. The Model 50 sold more than '''1 million units''' (Model 50 and Model 50 Z combined), making it the best-selling PS/2 by several orders of magnitude and IBM's top-selling personal computer for several years.
The '''IBM Personal System/2 Model 50''' (machine type '''8550''') is the entry-level Micro Channel PS/2: the cheapest of the original four models to get both '''MCA''' and '''VGA'''. It was announced on 2 April 1987 at a purchase price of '''US$3,595''' alongside the [[IBM PS/2 Model 30]], [[IBM PS/2 Model 60]] and [[IBM PS/2 Model 80]].<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>


A revised '''Model 50 Z''' (8550-031 / 061) shipped from June 2, 1988 with a redesigned planar carrying 85-ns DRAM (replacing the original 125-ns), enabling zero-wait-state memory access. The Z is roughly 20% faster than the original Model 50 in memory-bound work. The Model 50 Z also dropped the ST-506 Fixed Disk Adapter/A in favour of an ESDI controller for the 60 MB submodel, and replaced the dual 512 KB SIMM sockets with a single 1 MB or 2 MB SIMM socket.
A revised '''Model 50 Z''' (8550-031 and -061) followed in June 1988 with faster memory and zero-wait-state operation.<ref name="qref50z">IBM product information document GJAN-43VMLQ, "IBM PS/2 (Model 50 Z) — Technical specifications", mirrored at [https://www.ardent-tool.com/qtechinfo/GJAN-43VMLQ.html ardent-tool.com]. Source for the June 1988 announcement, zero-wait-state operation, the 72-pin 85 ns (or 120 ns) parity memory module, and the 30 MB (39 ms) and 60 MB (27 ms) drives.</ref>


== History ==
== Submodels ==


The original Model 50 (8550-021) launched at US $3,595 alongside the Model 60 ($5,295 / $6,295) and the Model 80 (starting at $6,995). By mid-1987 IBM's Boca Raton factory was producing approximately 1,000 Model 50s per day at peak demand, and the Model 50 became the best-selling PS/2 throughout the late 1980s. Within the first year IBM sold over 440,000 units, with an additional 650,000 projected for 1988. By April 1988 the Model 50 was the top-selling personal computer worldwide; it occupied that position through at least late 1989, and in the UK it was still the best-selling PC in mid-1990.
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+'''IBM PS/2 Model 50 / 50 Z submodels'''
! Submodel !! Wait states !! Memory !! Fixed disk !! Released
|-
| 8550-021 || 1 || 1 MB, two 512 KB modules at about 150 ns || 20 MB, 80 ms average access || April 1987
|-
| 8550-031 || 0 || 72-pin 85 ns (or 120 ns) parity module || 30 MB, 39 ms || June 1988
|-
| 8550-061 || 0 || 72-pin 85 ns (or 120 ns) parity module || 60 MB, 27 ms || June 1988
|}


The Model 50 received mixed press. Critics praised the tool-less industrial design (two thumbscrews at the rear cover, plastic captive push-pin tabs for drives, plastic thumbscrews for MCA cards) and the introduction of '''VGA''' + '''MCA''' as standard features. They criticised the slow 80286 + 1-wait-state memory (the Model 50 ran roughly the same speed as a contemporary Compaq Deskpro 286 despite the same clock) and the failure-prone Seagate ST-506 20 MB hard drive with its 85 ms access time. PC Magazine retrospectively named the Model 50 one of "The 20 Most Influential PCs of the Past 40 Years" for bringing VGA, 3.5-inch floppy drives, and tool-less construction to the personal computer market.
Memory and drive figures above are IBM's own.<ref name="qref50">IBM product information document GJAN-43VM6G, "IBM PS/2 (Model 50) — Technical specifications", mirrored at [https://www.ardent-tool.com/qtechinfo/GJAN-43VM6G.html ardent-tool.com]. Source for the one-wait-state 10 MHz operation, the two 30-pin 512 KB parity DRAM modules at approximately 150 ns, the three 3.5-inch half-height drive bays and the 80 ms access time of the 20 MB drive.</ref><ref name="qref50z" />


In June 1988 IBM introduced the '''Model 50 Z''' to address the performance criticisms. The Z planar replaced the 125-ns DRAM with 85-ns DRAM, eliminating the wait state. The dual-SIMM original was replaced with a single SIMM socket able to accept 1 MB or 2 MB modules (the original Model 50 only accepted 512 KB modules). The standard hard drive was upgraded to either a 30 MB ST-506 (-031) or a faster 60 MB ESDI (-061), with seek times rated twice as fast as the original 20 MB drive.
== Architecture ==


The Model 50 / 50 Z was discontinued in the catalogue around 1992 as IBM phased the 80286 PS/2 line out in favour of the [[IBM PS/2 Model 70|Model 70]] (80386 desktop) and PS/ValuePoint.
The Model 50 planar exists as P/N 90X9161 and P/N 15F6969; the Model 50 Z planar is FRU 90X9533.<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>


== Submodels ==
{| class="wikitable styled-table" style="width:95%;"
 
|+'''Model 50 planar &mdash; principal designators'''
<templatestyles src="Template:StyledTable/styles.css" />
! Designator !! Device
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|-
|+'''IBM PS/2 Model 50 / 50 Z submodels'''
| ZM36 || Intel 80286, 10 MHz
! Submodel !! Wait states !! Stock RAM !! Max RAM (planar) !! HDD !! Released !! Notes
|-
| ZM55 || 80287 math coprocessor socket
|-
| '''ZM47''' || '''Motorola MC146818A real-time clock'''
|-
| Y3 || 32.768 kHz crystal (real-time clock)
|-
| ZM13&ndash;ZM16 || ROM BIOS, four 27256 devices (32 KB each, 128 KB total)
|-
| ZM12 || 72X7377 DMA controller
|-
| ZM71 || 72X7385 bus controller
|-
| ZM74 || 72X8299 I/O controller
|-
| ZM75 || Intel 8272A diskette controller
|-
| ZM82 || Intel P8042AH keyboard controller
|-
| ZM84 || NS16550 UART
|-
| ZM96, ZM104 || 8259A interrupt controllers
|-
| ZM109 || 72X8287 VGA controller
|-
| ZM127 || Inmos IMSG171P-35 colour look-up table
|-
| ZM102&ndash;ZM117 (eight devices) || 4464 DRAM &mdash; 256 KB of video memory
|-
| ZM21, ZM22 || 30-pin SIMM sockets
|-
| J1 || Battery / speaker connector
|-
| J5 || Diskette riser slot
|-
| J9 || Fan connector
|-
| J10 || 16-bit channel connector, dedicated to the fixed-disk adapter
|-
|-
| 8550-021 || 1 || 1 MB || 1 MB || 20 MB ST-506 || April 1987 || Original Model 50; 125-ns DRAM. US $3,595
| J11 || 16-bit channel connector with the auxiliary video extension
|-
|-
| 8550-031 || 0 || 1 MB || 2 MB || 30 MB ST-506 || June 1988 || Model 50 Z; 85-ns DRAM
| J12, J13 || 16-bit channel connectors
|-
|-
| 8550-061 || 0 || 1 MB || 2 MB || 60 MB ESDI || June 1988 || Model 50 Z; ESDI drive
| F1 || 250 V / 3 A keyboard and mouse fuse
|}
|}


== Architecture ==
The system board carries 128 KB of ROM, a 64-byte CMOS RAM with the real-time clock, 256 KB of video memory, eight DMA channels, 16 levels of level-sensitive interrupts, the keyboard and auxiliary-device connectors with password security, the diskette controller (720 KB and 1.44 MB), an RS-232C serial controller and a bidirectional parallel controller.<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>
 
=== Real-time clock and battery ===
 
'''The Model 50's clock is not a Dallas module.''' It is a '''Motorola MC146818A''' soldered to the planar at ZM47, timed by the 32.768 kHz crystal at Y3, and backed by a '''separate 6 V lithium battery''' that lives in the '''battery and speaker assembly''' and plugs into J1.<ref name="at8550" /><ref name="m50tr" /> IBM's maintenance reference states that a 6 Vdc lithium battery maintains voltage to the real-time clock and CMOS RAM when the supply is off, and that the cover can be locked to prevent battery removal and the loss of the power-on password and configuration.<ref name="m50tr" /><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>
 
The assembly is FRU '''33F5950''' and the battery itself is IBM part '''72X8498''' &mdash; a 6 V two-cell lithium pack equivalent to a CR-P2 / DL223A camera battery. IBM's own caution is to use only that part, and IBM retain tip H024809 says to replace the battery when it measures below 5.5 Vdc '''out of the assembly'''.<ref name="atbatt">[https://www.ardent-tool.com/misc/Battery_Speaker_Assembly.html Battery/Speaker Assembly], Ardent Tool of Capitalism. Covers Models 50, 50 Z, 60, 65 SX, 70 and 80. Source for FRU numbers 33F5950 and 72X8498, the connector pinouts, the power-on password override and IBM retain tip H024809 (replace the battery below 5.5 V DC, measured out of the assembly).</ref><ref name="atbattx">[https://www.ardent-tool.com/misc/batteries.html PS/2 Batteries], Ardent Tool of Capitalism, based on content by Bob Eager and Peter H. Wendt. Cross-reference of PS/2 models to battery types: the Model 70 and the Model 80 both take FRU 72X8498, a 6 V two-cell lithium pack equivalent to a CR-P2 / DL223A / EL223AP / K223LA / PC223 camera battery.</ref><ref name="m50hmr" />
 
The same assembly is how a forgotten power-on password is cleared: with the machine off, short pins 2 and 3 together if the assembly has pins, or insert a meter lead into connector 1 and short the other end to frame ground if it does not; power on, let POST finish, then remove the short.<ref name="m50hmr" />
 
=== Micro Channel ===
 
'''Four channel connectors''', all 16-bit. One carries the auxiliary video extension, and '''one is occupied by the fixed-disk adapter''', which is why IBM's own announcement and hardware maintenance reference both describe the machine as having three expansion slots.<ref name="m50tr" /><ref name="m50hmr" /><ref name="ann49" /> There are no 32-bit slots and no ISA compatibility.
 
== Storage ==
 
=== Diskette ===
 
A 1.44 MB 3.5-inch drive on a bus adapter at the diskette riser slot. IBM specifies the drive at 300 rpm &plusmn;1.5 %, 500 kbps and 80 tracks.<ref name="ann49" />
 
These drives are '''direct drive''' &mdash; the Mitsubishi MF355C specification gives a DC brushless motor coupled straight to the spindle at 300 rpm, with no belt.<ref name="mf355c">Mitsubishi Electric, ''3.5 inch Flexible Disk Drive Standard Specifications, MF355C'', document UGD-0527A, February 1987. [[:File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf]]. Section 3 states that the disk rotation mechanism uses a DC brushless direct-drive motor to rotate the spindle directly at 300 rpm; the drive has no belt.</ref> Their real failure mode is the surface-mount electrolytics on the logic board going open-circuit or high-ESR, and the corrosion left behind.<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 card-edge; FRU 64F0162 pin-interface), for Al Savage's teardown of a Mitsubishi MF355W-99M3 identifying five failed surface-mount electrolytics — two 22 µF/16 V, one 1 µF/50 V and two 0.22 µF/50 V — for the diskette-controller dirt problem under the power-supply fan, 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-drive logic boards, and the technique of fitting through-hole parts to the surface-mount pads.</ref>
 
=== Fixed disk ===
 
The drive plugs directly into its adapter in slot J10; there is no ribbon back to the planar. Three adapters were used:<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>


The Model 50 planar (Type 1, original 8550-021) and the Model 50 Z planar (Type 2, 8550-031 / 061) are distinct designs but share the chassis, the integrated VGA, the MCA slots and most I/O. Differences are concentrated around the memory subsystem.
* '''ST-506 adapters''' FRU 90X8070 and 90X8642 &mdash; the 20 MB (-021) and 30 MB (-031) drives.
* '''DBA-ESDI riser''' FRU 90X9441 (bare) and 90X9571 (with BIOS) &mdash; the 60 MB drive on the -061.


=== Common architecture ===
'''The desktop "ESDI" drives are not true ESDI.''' They are Direct Bus Attachment units with the controller integrated into the drive, which is why swapping a bare riser for one with BIOS, or fitting a larger drive from a different family, does not simply work.<ref name="athdd50" /><ref name="atdba">[https://www.ardent-tool.com/storage/DBA_ESDI.html IBM DBA-ESDI Hard Drives], Ardent Tool of Capitalism. Source for the list of systems using Direct Bus Attachment (the Model 70 by drive-riser connector), the 2 × 36-pin edge-connector pinout transcribed from the Model 70 technical reference, and the component map of the WD387 60 MB drive logic board.</ref>


* '''CPU''': Intel 80286 in a 68-pin PGA socket, 10 MHz.
A drive that spins but is not seen, particularly after long storage, may be suffering '''stiction''' rather than an electronic fault.<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>
* '''Math coprocessor''': Intel 80287 socket adjacent to the 80286. Optional, 8 MHz operation.
* '''MCA bus''': '''Four 16-bit MCA''' expansion slots on the planar. Each slot has both the 16-bit MCA basic edge and is keyed to accept 16-bit and 8-bit MCA cards. No 32-bit MCA slots; no ISA compatibility.
* '''Integrated VGA''' on the planar with the IBM VGA gate-array implementation and an Inmos IMSG171P-style RAMDAC. Modes: 80×25 / 80×50 text, 640×480×16, 320×200×256, 720×400×16 text (8×16 character box). Output on 15-pin DSUB at rear. Analog monitors only.
* '''Integrated I/O''':
** PS/2 keyboard (Mini-DIN-6).
** PS/2 pointing-device port (Mini-DIN-6) — the keyboard and mouse ports are functionally identical at the 8042 controller but the BIOS expects each device on its designated port.
** Asynchronous serial (DB-25 male).
** Centronics parallel (DB-25 female).
* '''Floppy controller''': PS/2 single-cable interface integrated on the planar, 1.44 MB 3.5" half-height drive.
* '''Hard drive interface''': '''None on the planar''' — the hard drive is supplied through an MCA controller card. The drive itself plugs directly into a connector on the rear edge of the controller card, eliminating a separate ribbon cable to the planar. The Model 50 (8550-021) uses the '''IBM Fixed Disk Adapter/A''' (ST-506); the Model 50 Z 30 MB (8550-031) uses the same ST-506 controller; the Model 50 Z 60 MB (8550-061) uses the '''IBM ESDI Fixed Disk Adapter/A'''.
* '''BIOS''': 128 KB total, split between '''CBIOS''' (Compatible BIOS, for backward DOS compatibility) and '''ABIOS''' (Advanced BIOS, for protected-mode OS/2). Held in two 64 KB EPROM / mask-ROM chips at U-positions on the planar.
* '''CMOS / RTC''': Battery-backed via the '''Dallas DS1287''' / DS12887 integrated RTC + lithium-cell module. Stores SETUP configuration, date / time.
* '''Audio''': PC speaker only.


=== Memory subsystem ===
== Power Supply ==


* '''Model 50 (8550-021)''': '''Two''' 30-pin PS/2 SIMM sockets. Accept only '''512 KB''' parity SIMMs. 1 MB on planar (2 × 512 KB). Maximum planar memory: 1 MB. Additional RAM via MCA memory cards up to a system maximum of 7 MB.
'''94 W''', universal and automatic voltage-sensing &mdash; '''there is no voltage selector switch to set wrongly'''.<ref name="ann49" /><ref name="m50hmr" /> The unit is an ASTEC AA13621, IBM P/N 90X9527, FRU P/N 90X9366.<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> On the Model 50 the fan is a separate assembly plugged into the planar at J9, not built into the supply.<ref name="atpwr50" />
* '''Model 50 Z (8550-031 / 061)''': '''Single''' 30-pin PS/2 SIMM socket. Accepts '''1 MB''' or '''2 MB''' parity SIMMs. Maximum planar memory: 2 MB. Additional RAM via MCA memory cards up to a system maximum of 7 MB.


PS/2 SIMMs use an IBM-specific pinout that is similar to but '''not''' interchangeable with standard PC/AT 30-pin parity SIMMs. The originals on the Model 50 carried silver-cap "metal-can" DRAM chips; any PS/2-pinout SIMM with the right capacitance and speed (125-ns on Model 50, 85-ns on Model 50 Z) works as a replacement. The AST Advantage/2 16-bit MCA card with 4 MB pre-installed plus a SCSI controller is a documented aftermarket option that takes the Model 50 to its 7 MB ceiling.
'''The Model 50 has no &minus;5 V rail.''' IBM's hardware maintenance reference lists only three outputs:<ref name="m50hmr" />


=== Storage ===
{| class="wikitable styled-table" style="width:75%; text-align:center;"
|+'''Model 50 &mdash; minimum under-voltage sense levels'''
! Output !! Minimum under-voltage sense level
|-
| +5.0 Vdc || +4.5 Vdc
|-
| +12.0 Vdc || +10.8 Vdc
|-
| &minus;12.0 Vdc || &minus;10.2 Vdc
|}


* '''Floppy''': 1.44 MB 3.5" half-height, PS/2 single-cable interface. Drives are typically ALPS, Mitsubishi, Sony or YE-Data.
The service limits IBM gives for measuring a running machine are wider:<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>
* '''Hard drive''' (8550-021): Seagate ST-506 20 MB (the famously slow 85 ms-access-time drive PC Magazine reviewers criticised) on the IBM Fixed Disk Adapter/A MCA card.
* '''Hard drive''' (8550-031): Seagate ST-506 30 MB on the IBM Fixed Disk Adapter/A. Twice the seek-speed of the 20 MB drive.
* '''Hard drive''' (8550-061): 60 MB ESDI on the IBM ESDI Fixed Disk Adapter/A.


The ESDI Fixed Disk Adapter/A is the same MCA controller used in the Model 60 (70 MB), Model 80 (70 MB, 115 MB), and other ESDI-equipped PS/2 systems. The drive plugs directly into a rear-edge connector on the controller card.
{| class="wikitable styled-table" style="width:75%; text-align:center;"
|+'''Model 50 &mdash; power supply voltage check'''
! Rail !! Minimum !! Maximum
|-
| +5 Vdc || +3.7 V || +6.2 V
|-
| +12 Vdc || +9.0 V || +15.0 V
|-
| &minus;12 Vdc || &minus;9.0 V || &minus;15.0 V
|}


=== Chassis ===
'''Power off for ten seconds or more before switching back on.''' The supply generates its 'power good' signal on that basis, and that signal lights the green power-good lamp on the front of the machine. '''If the green light is not on, the supply is not working properly.'''<ref name="m50hmr" />


The Model 50 chassis is a low-profile desktop, 360 W × 420 D × 140 H mm, designed to sit under a monitor on a desk. Two thumbscrews at the rear release the cover, which slides back about 10 mm and lifts off. Inside, the planar mounts on the floor of the chassis; the MCA riser is at the rear; the drive cage runs across the front-right with the floppy and the hard drive controller card directly behind it. The PSU is on the left-front.
Other IBM figures worth having on the bench: heat output 494 BTU/hr (144.8 W); input 90&ndash;137 Vac or 180&ndash;265 Vac at 50&ndash;60 Hz &plusmn;3 Hz, drawing at most 2.7 A on the low range or 1.4 A on the high range; and a maximum allowable '''275 mA on the keyboard port and 300 mA on the auxiliary device port'''.<ref name="m50tr" /><ref name="m50hmr" /> Those last two are the numbers to check against when a keyboard or mouse blows the planar fuse.


Drives are held by IBM's plastic captive push-pin tabs (the system shipped with a small plastic "crowbar" tool to release them). MCA cards are released by plastic thumbscrews on the rear bracket.
== Chassis ==


=== Power Supply ===
A low-profile desktop, 360 mm wide, 420 mm deep and 140 mm high, weighing 9.55 kg.<ref name="m50tr" /> Drives and cards are held by IBM's plastic captive push-pin fittings rather than screws; the machine ships with a '''snap tool, IBM part 72X8547''', stowed inside the system unit in front of the battery.<ref name="m50hmr" /> '''Use it, or a plastic spudger &mdash; not a screwdriver.''' The pins are brittle with age.


'''94 W''' switching power supply, 110/220 VAC auto-sensing. PS/2 single-cable drive power feed integrated on the planar — '''no Molex 4-pin connectors'''. The 94 W is borderline for a fully-populated Model 50 with multiple MCA cards plus an ESDI drive; the Model 50 Z PSU is electrically the same.
The drive-structure removal tool and the planar centring pin are covered in the common-devices procedure for this chassis.<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>


== BIOS and Reference Diskette ==
== BIOS and Reference Diskette ==


The Model 50 has '''no built-in SETUP screen'''. All configuration is performed by booting the model-specific '''IBM PS/2 Reference Diskette''' that ships with the system. The Reference Diskette also reads each fitted MCA card's '''ADF (Adapter Definition File)''' and auto-configures interrupts, DMA channels and memory addresses.
No built-in SETUP. Everything is configured from the model-specific '''Reference Diskette''', which also reads each fitted adapter's '''ADF''' (adapter description file) and runs Auto Configuration, and carries Advanced Diagnostics under Ctrl-A. The Model 50 and Model 60 share Reference Diskette v1.08.<ref name="at8560">[https://www.ardent-tool.com/8560/index.html 8560 Planar], Ardent Tool of Capitalism. Component-designator map for the Model 60 planar (FRU 72X8538), including F1 (5MF 3 A / 250 V), J3 power connector, J14 battery/speaker connector, the MC146818A RTC at ZM6, the µPD446C-15L 2 KB NVRAM at ZM5, the four 30-pin SIMM sockets and the eight Micro Channel slots.</ref>
 
* '''Model 50 Reference Diskette''': version 1.07 final, supports both 8550-021 and 8550-031 / 061.
* '''Reference Diskettes are model-specific''' — a Model 30 or Model 60 Reference Diskette does not work on a Model 50.


ADF files for MCA cards are supplied on a separate "option diskette" that ships with each card. After fitting a new card, the ADF must be copied onto the working Reference Diskette before "Set Configuration → Run Auto Configuration" can complete; otherwise the system reports a '''165 card-ID-mismatch error''' at POST.
If a card's ADF is not on the working Reference Diskette, Auto Configuration cannot complete and POST reports a card-ID mismatch. Copy the ADF from the option diskette onto the working copy first.


The Reference Diskette also provides the '''Advanced Diagnostics''' menu (entered with Ctrl-A from the main menu) for FRU-level hardware testing.
Certain adapters &mdash; 3270 Connection, Token-Ring and PC Network &mdash; have installation restrictions and a configuration backup/restore caution on this chassis.<ref name="atstiction" />


== General Maintenance ==
== General Maintenance ==


Chassis opening, MCA card handling, drive maintenance and Dallas DS12887 RTC replacement procedures are documented in [[IBM PS/2 Model 50 Maintenance Guide]].
Opening the machine, the snap tool, card and drive handling, battery replacement and rail checks are in [[IBM PS/2 Model 50 Maintenance Guide]].


== Troubleshooting ==
== Troubleshooting ==


Audio beep codes, the full PS/2 numeric POST code reference, MCA-specific errors (165 card ID mismatch, 110 / 111 parity errors), the 161 / 162 / 163 RTC battery cluster and dead-system isolation are documented in [[IBM PS/2 Model 50 Troubleshooting Guide]].
Beep codes, the numeric POST code list, the 161/162/163 clock and battery cluster, card-ID mismatches and dead-system isolation are in [[IBM PS/2 Model 50 Troubleshooting Guide]].


== Capacitor Replacement ==
== Capacitor Replacement ==


Planar tantalums (10 µF / 16 V), the 94 W PSU recap, the ESDI controller card capacitors and the drive logic board recap procedure are documented in [[IBM PS/2 Model 50 Capacitor Replacement Guide]].
The planar decoupling (surface-mount tantalum and ceramic, '''not''' aluminium electrolytic), the 94 W supply and the drive logic boards are in [[IBM PS/2 Model 50 Capacitor Replacement Guide]].


== Gallery ==
== Gallery ==
<gallery mode="packed" heights="220">
<gallery mode="packed" heights="220">
File:IBM PS2 Model 50 system.jpg|IBM PS/2 Model 50 (8550-021) desktop
File:IBM PS2 Model 50 system.jpg|IBM PS/2 Model 50 (8550-021)
File:IBM PS2 Model 50Z external.jpg|IBM PS/2 Model 50 Z (8550-031 / 061)
File:IBM PS2 Model 50Z external.jpg|IBM PS/2 Model 50 Z
File:IBM PS2 Model 50Z internals.jpg|Model 50 Z internals showing planar, drive cage and MCA riser
File:IBM PS2 Model 50Z internals.jpg|Model 50 Z internals
File:IBM PS2 Model 50 badge.svg|Model 50 front badge
File:IBM PS2 Model 50 badge.svg|Model 50 front badge
File:IBM PS2 Model 50Z badge.svg|Model 50 Z front badge
File:IBM PS2 Model 50Z badge.svg|Model 50 Z front badge
</gallery>
</gallery>


== Related Pages ==
== References ==


* [[IBM PS/2 Model 50 Maintenance Guide]]
<references />
* [[IBM PS/2 Model 50 Troubleshooting Guide]]
* [[IBM PS/2 Model 50 Capacitor Replacement Guide]]
* [[IBM PS/2 Model 60]] — tower sibling
* [[IBM PS/2 Model 30]] — ISA-bus entry-level
* [[IBM PS/2 Model 70]] — 386 desktop successor
* [[IBM PS2 Model 50 Technical Reference (May 1988)]] — official IBM Technical Reference (PDF on the wiki)
* [[IBM PS2 Model 50 Technical Reference (October 1990)]] — updated Technical Reference (PDF on the wiki)
* [[IBM PS2 Model 50 Hardware Maintenance Reference]] — IBM HMR (PDF on the wiki)


== References ==
== Related Pages ==


* [https://en.wikipedia.org/wiki/IBM_PS/2_Model_50 IBM PS/2 Model 50 — Wikipedia]. Source for release dates, sales figures (1 million Model 50 / 50 Z units, 440,000 in first year), 125-ns vs 85-ns DRAM, tool-less construction, single-SIMM change on the Z, PC Magazine "20 Most Influential PCs" reference.
* [[IBM PS/2 Model 50 Maintenance Guide]] &middot; [[IBM PS/2 Model 50 Troubleshooting Guide]] &middot; [[IBM PS/2 Model 50 Capacitor Replacement Guide]]
* [https://www.dosdays.co.uk/computers/IBM%20PS2%20Model%2050/ibm_ps2_model_50.php IBM PS/2 Model 50 — DOS Days]. Source for the 94 W PSU rating, integrated VGA modes, proprietary PS/2 SIMM pinout, ESDI controller architecture, and AST Advantage/2 option.
* [[IBM PS/2 Model 60]] &mdash; the tower sibling
* [https://www.ardent-tool.com/qtechinfo/GJAN-43VM6G.html IBM PS/2 Model 50 — Technical Specifications], Ardent Tool of Capitalism (IBM document GJAN-43VM6G).
* [[IBM PS/2 Model 30]] &middot; [[IBM PS/2 Model 70]] &middot; [[IBM PS/2 Model 80]]
* [https://www.ardent-tool.com/qtechinfo/GJAN-43VMLQ.html IBM PS/2 Model 50 Z — Technical Specifications], Ardent Tool of Capitalism (IBM document GJAN-43VMLQ).
* '''IBM documentation hosted here:''' [[IBM PS2 Model 50 Technical Reference (May 1988)]] &middot; [[IBM PS2 Model 50 Technical Reference (October 1990)]] &middot; [[IBM PS2 Model 50 Hardware Maintenance Reference]] &middot; [[IBM PS2 Model 50 Schematics]]
* IBM, ''IBM Personal System/2 Hardware Maintenance Manual'' (S52G-9971-02, October 1994). Authoritative FRU listings and ECA recall data.


{{Navbox-IBMComputers|state=expanded}}
{{Navbox-IBMComputers|state=collapsed}}


[[Category:IBM]]
[[Category:IBM]]

Latest revision as of 00:20, 25 September 2026

IBM Personal System/2 Model 50
IBM PS/2 Model 50 (8550)
Specifications
DeveloperIBM Entry Systems Division, Boca Raton
ManufacturerIBM
TypeMid-range desktop personal computer
Released2 April 1987 (Model 50); June 1988 (Model 50 Z)
CPUIntel 80286 @ 10 MHz, 1 wait state (Model 50); 0 wait states (Model 50 Z)
Memory1 MB on the system board; 7 MB system maximum via channel memory
Storage1.44 MB 3.5" diskette; 20 MB or 30 MB fixed disk on an ST-506 adapter, or 60 MB DBA drive on a riser
DisplayVGA integrated on the system board, 256 KB video memory
SoundPC speaker
Dimensions360 mm W × 420 mm D × 140 mm H
Weight9.55 kg (21 lb)
OS / FirmwareIBM PC DOS 3.3 and later; IBM OS/2 1.x; IBM AIX PS/2
PredecessorIBM PC AT (5170)
SuccessorIBM PS/2 Model 70
Model no.8550

The IBM Personal System/2 Model 50 (machine type 8550) is the entry-level Micro Channel PS/2: the cheapest of the original four models to get both MCA and VGA. It was announced on 2 April 1987 at a purchase price of US$3,595 alongside the IBM PS/2 Model 30, IBM PS/2 Model 60 and IBM PS/2 Model 80.[1]

A revised Model 50 Z (8550-031 and -061) followed in June 1988 with faster memory and zero-wait-state operation.[2]

Submodels

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IBM PS/2 Model 50 / 50 Z submodels
Submodel Wait states Memory Fixed disk Released
8550-021 1 1 MB, two 512 KB modules at about 150 ns 20 MB, 80 ms average access April 1987
8550-031 0 72-pin 85 ns (or 120 ns) parity module 30 MB, 39 ms June 1988
8550-061 0 72-pin 85 ns (or 120 ns) parity module 60 MB, 27 ms June 1988

Memory and drive figures above are IBM's own.[3][2]

Architecture

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The Model 50 planar exists as P/N 90X9161 and P/N 15F6969; the Model 50 Z planar is FRU 90X9533.[4][5]

Model 50 planar — principal designators
Designator Device
ZM36 Intel 80286, 10 MHz
ZM55 80287 math coprocessor socket
ZM47 Motorola MC146818A real-time clock
Y3 32.768 kHz crystal (real-time clock)
ZM13–ZM16 ROM BIOS, four 27256 devices (32 KB each, 128 KB total)
ZM12 72X7377 DMA controller
ZM71 72X7385 bus controller
ZM74 72X8299 I/O controller
ZM75 Intel 8272A diskette controller
ZM82 Intel P8042AH keyboard controller
ZM84 NS16550 UART
ZM96, ZM104 8259A interrupt controllers
ZM109 72X8287 VGA controller
ZM127 Inmos IMSG171P-35 colour look-up table
ZM102–ZM117 (eight devices) 4464 DRAM — 256 KB of video memory
ZM21, ZM22 30-pin SIMM sockets
J1 Battery / speaker connector
J5 Diskette riser slot
J9 Fan connector
J10 16-bit channel connector, dedicated to the fixed-disk adapter
J11 16-bit channel connector with the auxiliary video extension
J12, J13 16-bit channel connectors
F1 250 V / 3 A keyboard and mouse fuse

The system board carries 128 KB of ROM, a 64-byte CMOS RAM with the real-time clock, 256 KB of video memory, eight DMA channels, 16 levels of level-sensitive interrupts, the keyboard and auxiliary-device connectors with password security, the diskette controller (720 KB and 1.44 MB), an RS-232C serial controller and a bidirectional parallel controller.[6]

Real-time clock and battery

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The Model 50's clock is not a Dallas module. It is a Motorola MC146818A soldered to the planar at ZM47, timed by the 32.768 kHz crystal at Y3, and backed by a separate 6 V lithium battery that lives in the battery and speaker assembly and plugs into J1.[4][6] IBM's maintenance reference states that a 6 Vdc lithium battery maintains voltage to the real-time clock and CMOS RAM when the supply is off, and that the cover can be locked to prevent battery removal and the loss of the power-on password and configuration.[6][7]

The assembly is FRU 33F5950 and the battery itself is IBM part 72X8498 — a 6 V two-cell lithium pack equivalent to a CR-P2 / DL223A camera battery. IBM's own caution is to use only that part, and IBM retain tip H024809 says to replace the battery when it measures below 5.5 Vdc out of the assembly.[8][9][7]

The same assembly is how a forgotten power-on password is cleared: with the machine off, short pins 2 and 3 together if the assembly has pins, or insert a meter lead into connector 1 and short the other end to frame ground if it does not; power on, let POST finish, then remove the short.[7]

Micro Channel

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Four channel connectors, all 16-bit. One carries the auxiliary video extension, and one is occupied by the fixed-disk adapter, which is why IBM's own announcement and hardware maintenance reference both describe the machine as having three expansion slots.[6][7][1] There are no 32-bit slots and no ISA compatibility.

Storage

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Diskette

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A 1.44 MB 3.5-inch drive on a bus adapter at the diskette riser slot. IBM specifies the drive at 300 rpm ±1.5 %, 500 kbps and 80 tracks.[1]

These drives are direct drive — the Mitsubishi MF355C specification gives a DC brushless motor coupled straight to the spindle at 300 rpm, with no belt.[10] Their real failure mode is the surface-mount electrolytics on the logic board going open-circuit or high-ESR, and the corrosion left behind.[11][12]

Fixed disk

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The drive plugs directly into its adapter in slot J10; there is no ribbon back to the planar. Three adapters were used:[13]

  • ST-506 adapters FRU 90X8070 and 90X8642 — the 20 MB (-021) and 30 MB (-031) drives.
  • DBA-ESDI riser FRU 90X9441 (bare) and 90X9571 (with BIOS) — the 60 MB drive on the -061.

The desktop "ESDI" drives are not true ESDI. They are Direct Bus Attachment units with the controller integrated into the drive, which is why swapping a bare riser for one with BIOS, or fitting a larger drive from a different family, does not simply work.[13][14]

A drive that spins but is not seen, particularly after long storage, may be suffering stiction rather than an electronic fault.[15]

Power Supply

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94 W, universal and automatic voltage-sensing — there is no voltage selector switch to set wrongly.[1][7] The unit is an ASTEC AA13621, IBM P/N 90X9527, FRU P/N 90X9366.[16] On the Model 50 the fan is a separate assembly plugged into the planar at J9, not built into the supply.[16]

The Model 50 has no −5 V rail. IBM's hardware maintenance reference lists only three outputs:[7]

Model 50 — minimum under-voltage sense levels
Output Minimum under-voltage sense level
+5.0 Vdc +4.5 Vdc
+12.0 Vdc +10.8 Vdc
−12.0 Vdc −10.2 Vdc

The service limits IBM gives for measuring a running machine are wider:[17]

Model 50 — power supply voltage check
Rail Minimum Maximum
+5 Vdc +3.7 V +6.2 V
+12 Vdc +9.0 V +15.0 V
−12 Vdc −9.0 V −15.0 V

Power off for ten seconds or more before switching back on. The supply generates its 'power good' signal on that basis, and that signal lights the green power-good lamp on the front of the machine. If the green light is not on, the supply is not working properly.[7]

Other IBM figures worth having on the bench: heat output 494 BTU/hr (144.8 W); input 90–137 Vac or 180–265 Vac at 50–60 Hz ±3 Hz, drawing at most 2.7 A on the low range or 1.4 A on the high range; and a maximum allowable 275 mA on the keyboard port and 300 mA on the auxiliary device port.[6][7] Those last two are the numbers to check against when a keyboard or mouse blows the planar fuse.

Chassis

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A low-profile desktop, 360 mm wide, 420 mm deep and 140 mm high, weighing 9.55 kg.[6] Drives and cards are held by IBM's plastic captive push-pin fittings rather than screws; the machine ships with a snap tool, IBM part 72X8547, stowed inside the system unit in front of the battery.[7] Use it, or a plastic spudger — not a screwdriver. The pins are brittle with age.

The drive-structure removal tool and the planar centring pin are covered in the common-devices procedure for this chassis.[18]

BIOS and Reference Diskette

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No built-in SETUP. Everything is configured from the model-specific Reference Diskette, which also reads each fitted adapter's ADF (adapter description file) and runs Auto Configuration, and carries Advanced Diagnostics under Ctrl-A. The Model 50 and Model 60 share Reference Diskette v1.08.[19]

If a card's ADF is not on the working Reference Diskette, Auto Configuration cannot complete and POST reports a card-ID mismatch. Copy the ADF from the option diskette onto the working copy first.

Certain adapters — 3270 Connection, Token-Ring and PC Network — have installation restrictions and a configuration backup/restore caution on this chassis.[15]

General Maintenance

[edit | edit source]

Opening the machine, the snap tool, card and drive handling, battery replacement and rail checks are in IBM PS/2 Model 50 Maintenance Guide.

Troubleshooting

[edit | edit source]

Beep codes, the numeric POST code list, the 161/162/163 clock and battery cluster, card-ID mismatches and dead-system isolation are in IBM PS/2 Model 50 Troubleshooting Guide.

Capacitor Replacement

[edit | edit source]

The planar decoupling (surface-mount tantalum and ceramic, not aluminium electrolytic), the 94 W supply and the drive logic boards are in IBM PS/2 Model 50 Capacitor Replacement Guide.

[edit | edit source]
  • IBM PS/2 Model 50 (8550-021)
    IBM PS/2 Model 50 (8550-021)
  • IBM PS/2 Model 50 Z
    IBM PS/2 Model 50 Z
  • Model 50 Z internals
    Model 50 Z internals
  • Model 50 front badge
    Model 50 front badge
  • Model 50 Z front badge
    Model 50 Z front badge

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 IBM Announcement Letter 187-049, "IBM Personal System/2 Model 50", 2 April 1987, reproduced at 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).
  2. ↑ 2.0 2.1 IBM product information document GJAN-43VMLQ, "IBM PS/2 (Model 50 Z) — Technical specifications", mirrored at ardent-tool.com. Source for the June 1988 announcement, zero-wait-state operation, the 72-pin 85 ns (or 120 ns) parity memory module, and the 30 MB (39 ms) and 60 MB (27 ms) drives.
  3. ↑ IBM product information document GJAN-43VM6G, "IBM PS/2 (Model 50) — Technical specifications", mirrored at ardent-tool.com. Source for the one-wait-state 10 MHz operation, the two 30-pin 512 KB parity DRAM modules at approximately 150 ns, the three 3.5-inch half-height drive bays and the 80 ms access time of the 20 MB drive.
  4. ↑ 4.0 4.1 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.
  5. ↑ 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.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 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".
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 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".
  8. ↑ Battery/Speaker Assembly, Ardent Tool of Capitalism. Covers Models 50, 50 Z, 60, 65 SX, 70 and 80. Source for FRU numbers 33F5950 and 72X8498, the connector pinouts, the power-on password override and IBM retain tip H024809 (replace the battery below 5.5 V DC, measured out of the assembly).
  9. ↑ PS/2 Batteries, Ardent Tool of Capitalism, based on content by Bob Eager and Peter H. Wendt. Cross-reference of PS/2 models to battery types: the Model 70 and the Model 80 both take FRU 72X8498, a 6 V two-cell lithium pack equivalent to a CR-P2 / DL223A / EL223AP / K223LA / PC223 camera battery.
  10. ↑ Mitsubishi Electric, 3.5 inch Flexible Disk Drive Standard Specifications, MF355C, document UGD-0527A, February 1987. File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf. Section 3 states that the disk rotation mechanism uses a DC brushless direct-drive motor to rotate the spindle directly at 300 rpm; the drive has no belt.
  11. ↑ 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 card-edge; FRU 64F0162 pin-interface), for Al Savage's teardown of a Mitsubishi MF355W-99M3 identifying five failed surface-mount electrolytics — two 22 µF/16 V, one 1 µF/50 V and two 0.22 µF/50 V — for the diskette-controller dirt problem under the power-supply fan, and for Peter Wendt's list of mechanical causes of a 162 at POST.
  12. ↑ 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-drive logic boards, and the technique of fitting through-hole parts to the surface-mount pads.
  13. ↑ 13.0 13.1 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.
  14. ↑ IBM DBA-ESDI Hard Drives, Ardent Tool of Capitalism. Source for the list of systems using Direct Bus Attachment (the Model 70 by drive-riser connector), the 2 × 36-pin edge-connector pinout transcribed from the Model 70 technical reference, and the component map of the WD387 60 MB drive logic board.
  15. ↑ 15.0 15.1 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.
  16. ↑ 16.0 16.1 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.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 8560 Planar, Ardent Tool of Capitalism. Component-designator map for the Model 60 planar (FRU 72X8538), including F1 (5MF 3 A / 250 V), J3 power connector, J14 battery/speaker connector, the MC146818A RTC at ZM6, the µPD446C-15L 2 KB NVRAM at ZM5, the four 30-pin SIMM sockets and the eight Micro Channel slots.
[edit | edit source]


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