IBM PS/2 Model 60 Capacitor Replacement Guide

IBM PS/2 Model 60 (8560)

Capacitor work on the IBM PS/2 Model 60 (machine type 8560, submodels 041 and 071) involves the planar, the power supply, the diskette drive and the fixed-disk drives and adapters. The Model 60 shares its chassis and power-supply family with the Model 65 SX and the IBM PS/2 Model 80. IBM's documents for the Model 60 (the Technical Reference and the 1994 Hardware Maintenance Manual with its parts list) stop at FRU level and give no capacitor values. The values below come from a reverse-engineered schematic of one supply and from published repairs, and each is credited.

Safety

The supply rectifies the mains. In the 225 W unit (IBM P/N 72X6665) the two primary reservoir capacitors, C5 and C6, are 1000 µF 200 V parts connected in series across the rectified mains so that the supply can run on 220 V, with a bank of 220 kΩ balancing resistors across each. They hold a dangerous charge after the supply is unplugged.

1. Switch off and unplug the mains lead.
2. Discharge each reservoir capacitor across its own terminals through a resistor (for example 1 kΩ, 5 W).
3. Check with a meter that both read near zero before touching the board.
4. Do not probe a powered primary side without an isolation transformer.

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

• The planar (FRU 72X8538) has through-hole yellow dipped tantalum capacitors and surface-mount ceramic capacitors, and no aluminium electrolytics, on Ardent Tool's photograph of a 90X8434 board.
• The power supply has the machine's large electrolytics and its mains filter capacitors.
• The diskette drive board has surface-mount electrolytics that go open or high-ESR. This is the best-documented capacitor fault on PS/2 machines of this age.
• The fixed disks are 5.25-inch full-height drives on a separate ST-506 or ESDI adapter card. No capacitor list has been published for either the drives or the adapters.

Planar

A shorted tantalum pulls its rail down. IBM's Type 2 supply latches all outputs off when an output is shorted, and restarts only after the fault is removed and the switch has been off for at least ten seconds.

Finding a shorted tantalum

1. Unplug the machine and discharge the supply.
2. Set a multimeter to its lowest resistance range or diode test.
3. 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.
4. All parts on a rail are in parallel, so a low reading identifies a shorted rail. Lift one leg of the suspect capacitor and measure again to find the part.
5. Replace it with a tantalum of the value printed on the old part and an equal or higher voltage, the right way round.

No designator-to-value list has been published for this planar; read the value from the part. The "10 µF 16 V, marked 106 16V" tantalum that minuszerodegrees.net describes applies to IBM's 51xx (PC, XT and AT) boards.

Power supply

The 041 was fitted with a 207 W supply and the 071 with a 225 W supply. All 8560, 8565 and 8580 supplies share one form factor and one pinout.

Supplies for the 8560, 8565 and 8580

Rating	Identification	Published internals
207 W	Fitted to the 8560-041	None
225 W	IBM P/N 72X6665, REV A58491, PEC 3978, red switch; Ardent Tool also lists a 225 W FRU 15F6548. Input 100–125 V 4.5 A or 200–240 V 2.5 A; output +12 V 7 A, +5 V 27.25 A, −12 V 0.39 A	Reverse-engineered schematic
242 W	Later 8580s	None
250 W	FRU 57F1600, IBM's 1994 replacement for all Models 60, 65 and 80	None

How the 225 W supply works

Eric Schlaepfer's notes on the 72X6665 describe it as an LLC resonant converter with a separate auxiliary bias supply:

• Thermistors RT1 and RT2 with resistors R117 and R118 limit inrush current into the series reservoir capacitors.
• The bias supply is a linear transformer supply fed through a triac. A preregulator senses about 180 V peak to peak and cuts the triac off part way through each mains cycle, so the bias voltage is about the same on 120 V or 220 V input.
• The PWM controller is an SG3524. It drives the bipolar power transistors (Q1 and Q2) through an isolation transformer.
• Trimmer R77 sets the output voltage by sampling both +5 V and +12 V, so the two rails move together.
• An overcurrent comparator watches the ripple current in the main transformer and latches the controller off; it also watches the current difference between the two Schottky diodes in the +12 V secondary.
• All three outputs have overvoltage and undervoltage comparators. Overvoltage latches the supply off; undervoltage only removes Power Good. Trimmer R50 sets the comparators' reference.
• The green power LED is driven from Power Good. The disk LED is switched by a transistor in the supply from a signal sent by the system board.

So a supply that shuts down and stays off until the switch has been off has latched on an overvoltage, an overcurrent or a short. A supply that runs with the power LED dark is holding back Power Good because an output is below its undervoltage threshold.

225 W supply electrolytics

Values are read from the reverse-engineered schematic of a 72X6665 / PEC 3978 unit and apply to that supply only. They are not an IBM specification, and nothing comparable has been published for the 207 W, 242 W or 250 W supplies. Check each part against your own board before ordering.

Electrolytic capacitors in the IBM 225 W supply, P/N 72X6665

Designator	Value	Circuit on the schematic
C5, C6	1000 µF 200 V	Primary reservoir, in series across the rectified mains
C16, C40	4700 µF 10 V	+5 V output, before the chokes
C41	470 µF 35 V	+5 V output, after the chokes
C18	4700 µF 16 V	+12 V output
C17	470 µF 35 V	−12 V, input of the LM7912 regulator
C19	47 µF 25 V	−12 V, output of the LM7912
C55	470 µF 35 V	Bias supply
C7	470 µF 35 V	SG3524 supply
C20	2200 µF 16 V	120/220 V preregulator
C56, C57	10 µF 50 V	120/220 V preregulator
C13, C14	22 µF 25 V	Base drive of power transistors Q1 and Q2
C34	10 µF 50 V	Power Good delay
C38	1 µF 63 V	VCC undervoltage comparator

The value of C39, on the +12 V output after choke L3, and of several other capacitors is marked "?" on the schematic because it could not be read from the unit; read those from the board.

Non-electrolytic parts on the same sheet: C1 and C2 across the mains in the EMI filter (values not read) and C3, C4, C52 and C53 (560 pF) from the mains lines to earth; C8 and C9 (1 µF 250 V) in the power stage beside Q1 and Q2; C10 (0.001 µF 1 kV) in series with R5 in the power stage; and C26 (0.1 µF 500 V) in the preregulator. Replace an across-the-line or line-to-earth capacitor only with a part 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 smell.

Recapping the supply

1. Remove the supply: take the rear drive carrier out of the drive support structure, unplug any 4-pin drive power leads and the planar power plug, remove the three screws holding the supply and pull it out.
2. Discharge each reservoir capacitor and check it with a meter.
3. Photograph both sides of the board. Record each electrolytic's value, voltage, size and polarity.
4. Fit 105 °C parts of the same capacitance and an equal or higher voltage, low-ESR where the original was.
5. Replace mains filter capacitors only with correctly rated safety parts.
6. Test the supply with a load on +5 V and +12 V before refitting, against the limits in the maintenance guide. R77 moves +5 V and +12 V together, so watch both rails if it has to be adjusted.

Ardent Tool's contributors add two faults that are not capacitors: a failed power switch (Peter Wendt reports that half of the Model 80 supplies failed with a broken switch, the red ones more often than the white) and a crackling noise that can come from the mains filter or from a loose mains lead.

Diskette drive board

The Model 60 uses the half-height card-edge drive, P/N 90X6766, FRU 72X8523, made by Mitsubishi, Alps and Sony; the later third-height drive is FRU 64F0162. The drive boards differ between makers, so read the values on the board in front of you.

Published PS/2 diskette drive recaps

Drive	Capacitors found	Source
Mitsubishi MF355W-99M3, P/N 90X6766, FRU 72X8523	Two 22 µF 16 V, one 1 µF 50 V and two 0.22 µF 50 V surface-mount electrolytics, open or high-ESR	Al Savage
Mitsubishi PS/2 drive	Two surface-mount electrolytics, replaced with 10 µF through-hole parts	ibmfiles.com
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

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, and cut the old capacitors in two with flush cutters to avoid tearing the pads. Jim Shorney found that the solder on leaking surface-mount capacitors often will not melt and the legs pull out instead. Add fresh solder and flux first, and check each pad is still bonded before fitting the new part.

Peter Wendt notes that Mitsubishi drives in these machines have capacitors that cause 6xx errors. Two faults that look like drive capacitors and are not:

• A 162 at POST caused by the drive. During POST the heads are stepped away 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 that window, and it is dropped from the configuration. Older ALPS drives are known for losing the damper cushion glued to the head assembly.
• 6xx errors from the planar. The diskette controller sits under the supply fan, collects dirt and leaks current between pins, which looks like a failed drive. Clean the planar before condemning the drive.

The drives are direct drive and have no belt.

Fixed disks and adapters

Model 60 fixed disks

Submodel	Drive (IBM FRU)	Adapter (IBM FRU)	Geometry and timing
8560-041	44 MB ST-506, 72X8541	ST-506 fixed disk adapter, 72X8540	733 cylinders, 17 sectors, 512 bytes per sector; 5 Mbit/s; 40 ms average access
8560-071	70 MB ESDI, 72X8519	ESDI fixed disk adapter, 92F0061	583 cylinders, 36 sectors, 512 bytes per sector; 10 Mbit/s; 30 ms average seek
Options	115 MB ESDI, 90X7392; 314 MB ESDI, 90X8745	ESDI fixed disk adapter

Sources: IBM's announcement letter and 1994 parts list.

Replace only drive or adapter capacitors that are visibly damaged or measure bad. Fred Spencer's table on Ardent Tool, taken from IBM's Personal System/2 Reference Guide, gives 31–39 W for the 44 MB and 70 MB drives, so a weak supply can look like a drive fault at spin-up. Before blaming electronics:

• A 1780 on an 8560-041: IBM retain tip H064300 says to check that the fixed-disk cables are fitted correctly.
• A drive that will not spin up after storage has stuck heads. Peter Wendt's remedies are a few power cycles, or unplugging the system unit, shaking it up and down and turning it sharply clockwise; never lift the front and drop it. Copy the data off as soon as it starts.
• 17xx and 104xx codes: see the error-code tables. IBM's list puts 1702 on the ST-506 adapter and 10483 on the ESDI adapter, then the system board.

Memory and adapter cards

No capacitor data has been published for the 80286 Memory Expansion Option or for IBM's Micro Channel adapters. IBM's action for 201 to 205 is to reseat the system-board memory, and for the 214 group to check for memory of the wrong type or in the wrong slot. The planar takes four 30-pin 256 KB parity modules.

After the work

1. Test the supply on its own, under load, against IBM's limits.
2. Refit it and start from the Reference Diskette, with the diskette in the drive at power-on.
3. Run Automatic Configuration if an adapter changed, then Advanced Diagnostics (Ctrl-A at the main menu).
4. Check that the green power LED lights, which shows Power Good.
5. 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

A Model 60 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;
• a supply output outside IBM's limits, or no Power Good (the green LED stays off);
• 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.

Related pages

• IBM PS/2 Model 60
• IBM PS/2 Model 60 Maintenance Guide
• IBM PS/2 Model 60 Troubleshooting Guide
• IBM PS/2 Model 50 Capacitor Replacement Guide
• IBM PS/2 Model 80 Capacitor Replacement Guide
• Capacitor Failure Symptoms
• Battery Explosion, Capacitor or Corrosion Damage
• Floppy Drive Repair
• Recommended Tools