Amstrad PCW 9256 Troubleshooting Guide
Amstrad's service manual for the Amstrad PCW 9256 has no fault-finding chart and no drive section; its service route was the RP3 diagnostic tool, which the alignment chart calls for, and board exchange.[1] The checks below use the manual's alignment figures and parts list, John Elliott's description of the PCW hardware, and the user guides for the related machines. Adjustment procedures are in the Amstrad PCW 9256 Maintenance Guide.
Warning: the main unit contains the mains power supply and a CRT. Read CRT Discharge Procedure before opening it.
Start-up
[edit | edit source]Like the other PCWs, the 9256 has no boot ROM. At reset the hardware feeds the Z80 a fixed stream of bytes that builds a short boot program in RAM, and that program loads the first sector of the disc in drive A. Dot matrix and daisywheel PCWs use slightly different boot programs.[2] A blank screen with no disc in the drive is therefore normal.[3]
| Symptom | Probable cause | Action |
|---|---|---|
| Nothing at all: no screen, no drive activity | No mains, F501 open, or a supply fault | Check the mains lead and plug. Check F501 (3.15 A time-lag) on the monitor board; if it has blown, find the short before replacing it. Then measure the supply outputs (below).[1] |
| Blank screen and beeps, no disc | Normal | Insert a start-of-day disc.[3] |
| Blank screen and beeps with a disc in the drive | Wrong or damaged disc, or a drive that cannot read it | Try a known-good system disc made for the 9256. LocoScript and CP/M versions written after the 9256 contain code to detect its floppy controller and 3.5-inch drives.[2] |
| Screen dark but the machine loads (drive light, beeps) | Brightness turned down, or a monitor fault | Turn up the brightness, then check the horizontal oscillator and the sub-brightness setting (below).[1] |
Power supply
[edit | edit source]The supply is on the monitor board: the STK7308 hybrid (IC501), switching transformer T501, two AN6531s (IC502, IC503) and an L7824V regulator (IC504), with the mains rectifier diodes D501–D504 and the 150 µF 400 V reservoir C505 in the mains area of the board.[1]
Amstrad measures the outputs at connector A, with CP101 disconnected and electronic loads on each output as in Fig. 2-1 of the manual:[1]
| Output | Load | Expected | Adjust with |
|---|---|---|---|
| 24 V | 1.2 A | 24 V ±1 V | No adjuster |
| 12 V | 1.2 A | 12 V ±0.01 V | VR502 |
| 5 V | 1.8 A | 5 V ±0.05 V | VR501 |
- F501 blown: look for a short in the mains area first, at the rectifier diodes, C505 and the STK7308, before fitting a new fuse.[1]
- 24 V outside 23–25 V: there is no adjuster for it. Check the L7824V regulator (IC504).[1]
- 12 V or 5 V low, noisy or out of reach of VR502 or VR501: suspect the supply electrolytics; see the Amstrad PCW 9256 Capacitor Replacement Guide and Capacitor Failure Symptoms.
Monitor
[edit | edit source]| Symptom | Check | Amstrad's figure |
|---|---|---|
| No raster, or picture will not lock horizontally | Horizontal oscillator, pin 5 of CP401, free running with no input | 15.625 kHz, set with VR404 |
| Picture too tall or too short | Vertical size with the RP3 or pattern disc | Borders I = K = 10 ±2 mm, set with VR405 |
| Uneven line spacing | Linearity, set by the deflection yoke position | A−B, J−K and L−J each 3 mm or less |
| Background glows, or screen too dim at minimum settings | Sub-brightness, with brightness and contrast at minimum | A dim pattern, set with VR402 |
The CRT is a 310GNBWD (272814). Its socket, J801, is on the CRT board (MS0227), and the flyback transformer is FB401 (2014001).[1]
Disc drive
[edit | edit source]The drive is a UODC-45A 3.5-inch 720K unit (272508).[1] Elliott's notes say the 9256's floppy controller does not fully decode drive numbers in the same way as the 8256's: on a 9256, 9512+ or PCW 10, drive 2 appears to answer for drive 1 but always reports "ready", and selecting drive 3 selects both drives at once.[2] The manual gives no drive adjustments; clean the heads and check the drive as described in Floppy Drive Repair.
Printer
[edit | edit source]The printer is the 8256's 9-pin dot matrix mechanism, Amstrad part 171127, and the user-level printer checks in the 8256 troubleshooting guide apply: bail bar, paper, on-line state, ribbon cassette and head lever.[1][4] If the printer misbehaves after a repair, check the strobe timing: with the RP3 printer test running, VR701 on the printer board is turned until the RP3 reports "OK", neither too long nor too short.[1] The printer control logic is the Amstrad 40026 (IC701), with an NE556 (IC702) and two DN8695 drivers (IC706, IC708).[1] Only the Amstrad printer can be used on the printer socket.[1]
Keyboard
[edit | edit source]The keyboard has its own controller, the Amstrad 40027 (IC301), clocked by a 5 MHz ceramic resonator (X301), and connects through a DIN cord (CD303).[1] The PCW keyboard sends its data serially on a data line and a clock line that both idle high.[2] If no key works, check the cord and its plug first; a keyboard from another 9256 is a direct replacement.
Related pages
[edit | edit source]- Amstrad PCW 9256 · Amstrad PCW 9256 Maintenance Guide · Amstrad PCW 9256 Capacitor Replacement Guide
- Amstrad PCW 8256 Troubleshooting Guide · Amstrad PCW 9512+ Troubleshooting Guide
- Floppy Drive Repair · CRT Discharge Procedure · Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 Amstrad plc, PCW9256 Personal Computer Word Processor Service Manual. Hosted as File:Amstrad PCW 9256 Service Manual.pdf, described at Amstrad PCW 9256 Service Manual. Technical specification and safety tests p. 2; alignment instructions p. 3; monitor/CRT board layout p. 4; electrical parts list pp. 16–17.
- ↑ 2.0 2.1 2.2 2.3 John Elliott, PCW Hardware. Hosted as File:PCW Hardware Reference (John Elliott).pdf, described at Amstrad PCW Hardware Reference (John Elliott). Section 2 (boot process), section 6.1 (the PCW8256/8512/9256/10 printer controller), sections 8.2–8.3 (drive decoding on the 9256, 9512+ and 10, and the controller probe).
- ↑ 3.0 3.1 Richard Lloyd, PCW article ("Fifty two years and counting"), Amstrad CPC User Club Magazine (ACUC) issue 1, June 2022. Scan at archive.org. Retrieved 2026-10-02. A PCW started without a disc shows a blank screen and beeps; a suitable disc gives a series of lines moving down the screen.
- ↑ Amstrad, The PCW8256 and PCW8512 User Guide and Guide to Locomotive Software's LocoScript (AMSOFT, 1985). Hosted as File:Amstrad PCW8256 PCW8512 User Guide (1985).pdf, described at Amstrad PCW 8256 / PCW 8512 User Guide. Appendix I, Troubleshooting, pp. 141–143.