Amstrad PCW 9256 Capacitor Replacement Guide

PCW9256 monitor/CRT board; the supply's electrolytics are in the 500 series (service manual p. 4)

The Amstrad PCW 9256 has its power supply on the monitor board, and that supply feeds the computer, the drive and the printer. Amstrad's electrical parts list gives every electrolytic capacitor in the machine with its value, voltage and part number: nineteen entries covering 30 positions.

Safety

Warning: the main unit runs from the mains and contains a CRT. C505, 150 µF 400 V, holds a dangerous charge after the plug is pulled.

• Unplug the machine and discharge the tube; see CRT Discharge Procedure.
• Measure across C505 and discharge it through a suitable resistor before touching the board. Amstrad's board drawing outlines the area at mains potential and marks it "danger mains voltage"; the mains fuse F501 (3.15 A time-lag) and the rectifier diodes D501–D504 are inside it.
• After the work, run Amstrad's safety tests: a 4 kV flash test and an insulation resistance of at least 4 MΩ, both between the joined mains live and neutral and all accessible metal on the outside.

How the parts are numbered

The parts list numbers parts by circuit: the 500 series is the power supply (IC501 STK7308, IC502 and IC503 AN6531, IC504 L7824V, switching transformer T501, fuse F501); the 400 series is the deflection circuit (IC401 µPC1379C, horizontal drive transformer T401, flyback FB401); the 300 series is the keyboard (IC301, the 40027 keyboard controller); the 700 series is the printer control circuit (IC701, the 40026); and the 800 series is the CRT board (CRT socket J801).

Electrolytic capacitors

PCW9256 electrolytic capacitors (service manual p. 17)

Ref	Value	Voltage	Amstrad part no.
C523	0.1 µF	50 V	150908
C303, C414, C420, C422	1.0 µF	50 V	157563
C426	1.0 µF	160 V	272638
C506	1 µF	250 V	157564
C404	2.2 µF	50 V	157672
C429	10 µF	25 V	254024
C417, C419, C520, C521, C522, C528	10 µF	50 V	240462
C427	10 µF	160 V	170608
C801	22 µF	63 V	157647
C524	33 µF	50 V	254025
C305, C719	47 µF	10 V	157648
C512	100 µF	50 V	272784
C505	150 µF	400 V	157792
C507, C723	220 µF	35 V	201722
C525	470 µF	10 V	270963
C518, C526	470 µF	35 V	150919
C519	470 µF	50 V	272785
C418	1000 µF	25 V	152567
C720	1000 µF	35 V	271229

Amstrad marks the entry for C507 and C723 with its safety warning symbol, as it does other safety-critical parts; replace them with parts of the same specification. The list has no separate tantalum section. The manual notes that Amstrad reserved the right to supply selected resistors and capacitors only. Read the value and voltage on each part before removing it, since boards in the field may differ from the list.

Where to start

The 500-series parts belong to the power supply, with C505 as the 400 V reservoir. If any output is low, noisy or out of reach of its adjuster, start with these. The 400-series parts are in the deflection circuit, and C719, C720 and C723 in the printer control circuit. For what failed parts look like, see Capacitor Failure Symptoms.

Procedure

1. Unplug the machine, open the case, and discharge the CRT and C505.
2. Photograph the board and note the value, voltage and polarity of each electrolytic before removing it.
3. Remove each capacitor and clean the pads. Check under the larger supply capacitors for leaked electrolyte and corroded tracks.
4. Fit new parts of the same capacitance and the same or a higher voltage rating, observing polarity. Use a 400 V part at C505.
5. Inspect and reflow any cracked joints round T501, the STK7308 and the heat-sinked regulators.
6. Reassemble, then check the supply outputs before refitting the cover.

After the recap

Check and set the outputs at connector A as Amstrad's chart specifies, with CP101 disconnected, VR401 at maximum and an electronic load on each output (Fig. 2-1 of the manual):

Supply settings (service manual p. 3)

Output	Load	Setting	Adjuster
24 V	1.2 A	24 V ±1 V	None; check only
12 V	1.2 A	12 V ±0.01 V	VR502
5 V	1.8 A	5 V ±0.05 V	VR501

Reconnect CP101, run the picture adjustments in the Amstrad PCW 9256 Maintenance Guide, and repeat the safety tests.

Related pages

• Amstrad PCW 9256 · Amstrad PCW 9256 Maintenance Guide · Amstrad PCW 9256 Troubleshooting Guide
• Amstrad PCW 8256 Capacitor Replacement Guide · Amstrad PCW 9512+ Capacitor Replacement Guide
• Capacitor Failure Symptoms · CRT Discharge Procedure · Recommended Tools