Amstrad PCW 9512 Capacitor Replacement Guide

PCW9512 main unit, keyboard and daisywheel printer. The printer takes its power from the main unit.

The Amstrad PCW 9512 carries its screen, power supply, disc drive and computer board in one casting, and the supply also powers the daisywheel printer through the printer cable. Amstrad published a 44-page service manual for the 9512 with circuit and wiring diagrams. The Centre for Computing History holds a scanned copy, exhibit CH27485, which it offers to show on request; the manual has not been published online, so no capacitor values for the 9512's own boards are available.

Safety

Warning: the main unit runs from the mains and contains a CRT. The supply's mains reservoir capacitor and the tube both hold a dangerous charge after the plug is pulled.

• Unplug the machine and the printer before opening the case.
• Discharge the tube before working near it; see CRT Discharge Procedure.
• Find the supply's mains reservoir capacitor and measure across it before touching the board. On the PCW 8256 it is C5005, 100 µF 400 V, and on the later 9512+ it is C5005, 150 µF 400 V; both sit in an area that Amstrad's drawings outline as being at mains potential.
• After the work, run the safety tests Amstrad sets for its later PCWs: a 4 kV flash test and an insulation resistance of at least 4 MΩ between the joined mains live and neutral and all accessible metal on the outside of the case.

Opening the case

The Joyce Computer Club's notes on the 9512 say the case is held by six screws, four on the back and two on the sides, and that both knobs of the screen controls on the side have to be pulled off before the case will come away. The rear carries the power switch, the horizontal and vertical hold controls, the expansion edge connector, the 25-way parallel port and the printer socket.

What is inside

PCW9512 main unit

Part	Detail
Construction	Screen, power supply, drive and computer board in one casting
Printer supply	The daisywheel printer has no supply of its own; power and most of its control electronics come from the main unit
Disc drive	EME-232 3-inch drive, hard-wired as drive A; its power connector matches the 8256/8512 drive's but the wire colours are reversed
Printer controller	A PCW9512-specific controller, which also runs the parallel port
Floppy controller	The same type as the 8256 and 8512

Neighbouring models with published lists

Amstrad's service manuals for the PCW 8256 and 8512 and for the later PCW 9512+ list every electrolytic capacitor with its value, voltage and part number. Neither covers the 9512's boards.

Published capacitor lists for related PCWs

Model	Boards documented	Mains reservoir	Wiki list
PCW 8256 / 8512	Monitor board with the supply (5000 series), deflection (4000 series), CPU board (100 series), keyboard (800 series)	C5005, 100 µF 400 V	Amstrad PCW 8256 Capacitor Replacement Guide
PCW 9512+	Monitor/CRT board MM0041A with the supply, main board MC0130A, printer control circuit (700 series)	C5005, 150 µF 400 V	Amstrad PCW 9512+ Capacitor Replacement Guide

Sources: the 8256/8512 and 9512+ service manuals.

The 9512+ is the closer relation in function, since it also drives a daisywheel printer from the main unit's supply, but it came four years later with a different main board and a 3.5-inch drive. Use either list for comparison only. If a board in your 9512 carries the same board number as one in those manuals, its list can be checked against your parts one position at a time; otherwise read every value from the part fitted.

Recording your own board

1. Photograph both sides of each board before removing anything, with the board number in shot. Amstrad prints a board code on each PCW board, such as MC0130A and MM0041A on the 9512+.
2. For each electrolytic, write down the designator, capacitance, voltage, temperature rating, can diameter and height, and which way round it is fitted.
3. On the 8256 and 9512+, Amstrad numbers parts in series by circuit: 5000 for the power supply, 4000 for deflection, 700 for the printer control circuit and 100 for the logic board. Check whether your 9512 follows the same scheme before relying on it to find the supply parts.
4. Read the value from the sleeve of each part, not from a list for another model.
5. Keep the table with the machine.

Where to start

Start with the supply: the mains reservoir, the capacitors round the switching transformer, and the output smoothing capacitors. Those parts feed the printer as well as the computer. Then work through the deflection circuit if the picture is unstable or shrinks, and the logic board last. Capacitor Failure Symptoms shows what failed parts look like.

Procedure

1. Unplug the machine and printer, remove the screen knobs and case screws, and lift off the case.
2. Discharge the CRT and the mains reservoir capacitor.
3. Record every electrolytic as above before removing any of them.
4. Remove one capacitor at a time, clean the pads and look under the larger parts for leaked electrolyte and corroded tracks.
5. Fit a new part of the same capacitance and the same or a higher voltage rating, the right way round. Keep the mains reservoir at its original voltage rating or above.
6. Check for cracked solder joints round the switching transformer, the heat-sinked parts and the connectors while the board is out.
7. Reassemble and run the safety tests before refitting the case.

After the recap

Amstrad's alignment figures for the 9512 are in its unpublished service manual. The 8256 chart sets the 12 V and 5 V outputs with VR5002 and VR5001, and the 9512+ chart sets the same two outputs under load and also checks a 24 V output; both apply only to boards that match those manuals. Check that the machine boots from a start-of-day disc and that the printer feeds and prints before closing the case. The horizontal and vertical hold controls on the back correct a picture that rolls or tears after the work.

Related pages

• Amstrad PCW 9512 · Amstrad PCW 9512 Maintenance Guide · Amstrad PCW 9512 Troubleshooting Guide
• Amstrad PCW 9512+ Capacitor Replacement Guide · Amstrad PCW 8256 Capacitor Replacement Guide
• Capacitor Failure Symptoms · CRT Discharge Procedure · Recommended Tools