IBM PS/2 Model 30 Capacitor Replacement Guide

Capacitor replacement on the IBM PS/2 Model 30 (machine type 8530), both the original 8086 Model 30 and the Model 30 286, involves the planar, the power supply, the diskette drive boards and ISA cards.

IBM serviced the Model 30 at board level. Its Technical Reference, the Model 30 286 Hardware Maintenance Reference and the 1994 maintenance manual give no capacitor values; the Technical Reference specifies the power supply only by its ratings, regulation, protection levels, Power Good signal and connector pins. The planar schematics hosted here are logic drawings made in 1991 by Maintenance Information Technologies, not IBM. They have no parts list and show only a few of the planar's capacitors. Read the value and voltage printed on each part before removing it, and replace like for like: the same capacitance, an equal or higher voltage rating, and the same type.

Safety

The power supply rectifies the mains directly, so its primary reservoir capacitor charges to at least the peak of the mains (about 325 V on 230 V mains) and keeps that charge after the plug is pulled. It can kill.

1. Switch off and unplug the mains lead.
2. Discharge the reservoir capacitor through a resistor (for example 1 kΩ, 5 W) across its terminals. Do not short it with a screwdriver.
3. Check with a meter on a DC range that it has fallen to a few volts before touching the board.

The Model 30 286 supply has a voltage switch on the rear. IBM's instruction is to set it to 100–125 V or 200–240 V before the power cord is plugged in. The 8086 Model 30 supply accepts 120 V or 220/240 V without a switch.

There is no CRT in the Model 30. If you are also working on a PS/2 display, see CRT Discharge Procedure.

Capacitor types on the Model 30

• Tantalum capacitors, on ISA cards and on the planar if any are fitted. They are polarised and fail either short circuit, which overloads the supply so the machine will not start, or open circuit. A failed tantalum often shows no visible damage.
• Aluminium electrolytics in the power supply and on the diskette drive boards. They dry out, lose capacitance and gain ESR. The surface-mount electrolytics on PS/2 diskette drive boards also leak and corrode the board.
• Line-suppression (X and Y class) capacitors on the supply's mains input. Aged ones rupture; a RIFA part does so with smoke and a strong foul odour, and its fluid should not be touched.

The Model 30 286's clock module (a Dallas DS1287 at ZM35) has its own sealed lithium cell. It plugs into a socket and is a battery job, not a capacitor job; see the maintenance guide.

Planar capacitors

The 8086 planar exists as the original P/N 61X8823 and two later Greenock builds, P/N 33F4888 and FRU 33F8474. Their reference designators are largely the same, and largely the same as on the 8086 Model 25. The 286 planar exists as an early build with a PGA processor socket and a later one with a PLCC socket, FRU 34F0046. Neither IBM nor these maps give capacitor values. The 1991 schematics give values for a few positions: on the 8086 planar, C77 (10 µF) on the real-time clock's supply pin and C14 (2.2 µF) in the beeper driver; on the 286 planar, C60 (22 µF 16 V, polarised) in series with the speaker, and C29 and C30 (both 22 µF 50 V, polarised) in the video circuit, C29 on the +5 V feed through L1. Not every orange part on an IBM board is a tantalum; some are ceramic.

A shorted tantalum pulls its rail down and the supply shuts down. The supply only raises Power Good once every rail is above its under-voltage sense level, so POST never starts.

Finding a shorted tantalum

1. Discharge the supply as above.
2. Take the planar out. IBM's order for the Model 30 286 is adapters, bus adapter (riser), memory packs and coprocessor, then disconnect all cables from the system board.
3. Set a multimeter to its lowest resistance range or diode test.
4. Measure each tantalum in circuit, black lead to ground and red to the positive side. A good part reads high after a brief charging pulse; a shorted one reads close to 0 Ω.
5. Everything on a rail is in parallel, so a low reading identifies a shorted rail. To find the part, lift one leg of the suspect capacitor and measure it again off the board.
6. Before removing anything, photograph the part and note its printed value and polarity mark.

Removal and replacement

1. Record the polarity.
2. Add fresh solder and flux to both joints from the underside.
3. Heat one joint and lift that side of the part with tweezers, then do the other.
4. Clear the holes with solder wick.
5. Fit a replacement of the recorded value at an equal or higher voltage rating, positive leg to the positive hole.
6. Solder, inspect the joints and trim the leads.

Power supply

The Model 30 supply is a 70 W, four-output unit: 9.0 A at +5 V, 1.8 A at +12 V, 110 mA at −5 V and 300 mA at −12 V. It has an internal input fuse and shuts itself down on over-current or under-voltage. The Model 30 286 supply is rated 90 W. IBM's FRU numbers are 61X8905 for the Model 30 supply and 27F4166 for the Model 30 286. The Technical Reference, the Hardware Maintenance Reference and the maintenance manual give no internal parts list for either supply, so the values you need are the ones printed on the parts.

Reasons to open the supply:

• A rail outside the measurement limits (see the maintenance guide).
• Power Good does not come up with the planar stripped to its minimum.
• Bulging, leaking or vented capacitors, or smoke and a strong odour from the mains input.

Recapping:

1. Discharge the reservoir capacitor and check it with a meter.
2. Remove the supply and open the case.
3. Photograph the board. Record each electrolytic's value, voltage, temperature rating and polarity.
4. Desolder each electrolytic. On an aluminium electrolytic the stripe marks the negative lead, the opposite of the "+" on a tantalum.
5. Fit 105 °C low-ESR parts of the same capacitance and an equal or higher voltage.
6. Replace any cracked, bulging or leaking suppression capacitor with one of the same capacitance, the same or higher AC voltage rating and the same safety class (X2 for X2, Y2 for Y2).
7. Test the supply on a resistive load before connecting it to the planar.

Diskette drive boards

Leaking surface-mount electrolytics on the drive's logic board are the commonest capacitor fault in PS/2 machines of this age. The electrolyte corrodes the pads and tracks, so an old drive may need track repair as well as new capacitors. PS/2 drives were made by several suppliers, so the values differ; read the board in front of you. Three published repairs:

Published PS/2 diskette drive recaps

Drive	Capacitors found	Source
ALPS PS/2 drive	One 4.7 µF 25 V, one 10 µF 16 V and three non-polarised 4.7 µF 16 V. The drive's separate controller board has its own capacitors, which vary with the machine the drive came from.	Mac84
Mitsubishi PS/2 drive	Two surface-mount electrolytics, replaced with 10 µF through-hole parts	ibmfiles.com
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, found open or high-ESR	Al Savage, at Ardent Tool

Mitsubishi MF355W-99M3 drive board (FRU 72X8523) with the five failed surface-mount electrolytics marked. (Photo: Al Savage, via Ardent Tool of Capitalism)

FRU 72X8523 is the half-height 1.44 MB drive in IBM's Model 30-286 parts list. Non-polarised capacitors must be replaced with non-polarised parts.

Mitsubishi's specification for its MF355C 3.5-inch drive describes a brushless DC motor that turns the spindle directly at 300 rpm, so a drive of that design has no belt. A drive that will not spin up needs its board and motor checked.

ISA cards

A shorted tantalum on a card holds the supply down just as one on the planar does. Ardent-tool's check is to measure Power Good, which should read +3.5 to +5 V on a running system; if it does not, remove all adapters, cables and extra memory, and if Power Good then appears, refit them one at a time to find the faulty one.

Polarity

On an aluminium electrolytic the stripe marks the negative lead. On a tantalum the "+" marks the positive lead. Tantalums must go in the right way round.

Tantalum polarity marking on an IBM 5150 motherboard (minuszerodegrees.net). The Model 30 planar is a different board.

A failed tantalum on an IBM 51xx motherboard; the small black hole is the only visible sign (minuszerodegrees.net).

After the work

IBM's minimum under-voltage sense levels are the points below which the supply withholds Power Good:

Model 30 and Model 30 286 under-voltage sense levels

Output	Sense level
+5 V	+4.5 V
−5 V	−4.3 V
+12 V	+10.8 V
−12 V	−10.2 V

Power Good should read +3.5 to +5 V with the system running. IBM specifies it as TTL-compatible, 2.4 to 5.25 V when active and 0.0 to 0.4 V when inactive, with a turn-on delay of 100 to 500 ms. The pin-by-pin limits at P3 and P4 are in the maintenance guide.

1. Power up with no adapters or external devices. A successful POST ends with one short beep.
2. Boot the Starter Diskette and check the configuration.
3. Run the Advanced Diagnostics diskette and test each subsystem.

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

When not to recap

A Model 30 that passes POST and runs reliably does not need its planar capacitors changed; each desoldering risks lifting a pad. Act when:

• a capacitor is bulging, leaking or vented;
• the supply is out of limits or smells burnt;
• the procedure above finds a shorted tantalum;
• a diskette drive is unreliable and its board shows leaked electrolyte.

Related pages

• IBM PS/2 Model 30
• IBM PS/2 Model 30 Maintenance Guide
• IBM PS/2 Model 30 Troubleshooting Guide
• IBM PS/2 Model 25 Capacitor Replacement Guide
• Capacitor Failure Symptoms
• Battery Explosion, Capacitor or Corrosion Damage
• Floppy Drive Repair