Amstrad PCW 8256 Troubleshooting Guide
Faults on the Amstrad PCW 8256 fall into four areas: the power supply and monitor in the monitor unit, the 3-inch drive, the printer, and the keyboard. Amstrad's own service route was to diagnose with its R.P.3 diagnostic tool and exchange boards, drive mechanisms and printer mechanisms; the service manual says full diagnostics are not in it, and its flow charts cover only the disc drives.[1] The user-level checks below come from Amstrad's user guide, and the Amstrad PCW 8256 Maintenance Guide has the adjustment procedures. The same faults and fixes apply to the Amstrad PCW 8512, whose second drive is covered in the Amstrad PCW 8512 Troubleshooting Guide.
Warning: the monitor unit contains the mains power supply and a CRT. Read CRT Discharge Procedure before opening it.
Start-up symptoms
[edit | edit source]The PCW has no boot ROM. At switch-on the hardware hands the Z80 a short boot program, which loads the first sector of the disc in drive A; until a disc loads there is nothing else on screen.[2]
| Symptom | Probable cause | Action |
|---|---|---|
| No bright screen when the power button is pressed | No mains, plug fuse, or a fault in the supply | Check the socket with a lamp and the plug wiring and fuse. Disconnect and reconnect the keyboard and printer, remove any RS232C/Centronics interface, and try again.[3] Then check F5001 (2 A time-lag) and the supply rails, below.[1] |
| Blank screen and beeps with no disc in the drive | Normal: there is no ROM to show anything | Insert a start-of-day disc and press the space bar.[4] |
| Screen stays bright or flashes, then bleeps a few times, with a disc in the drive | Not a start-of-day disc, or a damaged disc | Check the disc. Try the master disc; if that loads, make a new start-of-day disc.[3] |
| Blank screen with the system disc in drive A; the drive motor can be heard but the disc does not turn | Perished drive belt | Replace the belt; see drive belt.[4] |
| The pattern of lines appears but the wrong program loads | Wrong disc or wrong side | Insert the right disc with the wanted side to the left and press Shift, Extra and Exit together.[3] |
| Keys do nothing | Keyboard plug, keyboard or monitor unit | Unplug and refit the keyboard. If it still fails, try another PCW 8256 or 8512 keyboard.[3][4] |
Power supply and monitor
[edit | edit source]The monitor board carries the supply for the whole machine, including the printer. The main parts are the STK7308 hybrid (IC5001), switching transformer T5001, two AN6531s (IC5002, IC5003) and an AN78N24 (IC5004). The mains fuse F5001 is 2 A time-lag, 250 V.[1]
| Output | Measure at | Set with | Tolerance |
|---|---|---|---|
| 12 V | Pin 2 of CD102, CD101 disconnected | VR5002 | ±2% |
| 5 V | Pin 3 of CD102, CD101 disconnected | VR5001 | ±2% |
Turn the brightness control VR2001 to maximum while setting both outputs, as Amstrad's chart does.[1]
- A blown F5001 points to a short on the primary side. Find it before fitting a new fuse: check the mains rectifier diodes D5001–D5004 (20E10), the 400 V reservoir C5005 and the STK7308.[1]
- Outputs that are low, noisy or that will not adjust into tolerance point to the supply's electrolytics; see the Amstrad PCW 8256 Capacitor Replacement Guide and Capacitor Failure Symptoms.
- With the supply correct but no picture, check the horizontal oscillator: free running with no input, pin 1 of CP4001 should read 15.625 kHz, set with VR4005.[1]
- A picture that rolls is first a matter for the vertical hold (VR4001, a separate pot on the cabinet), then for VR4002 and VR4003 in Amstrad's alignment.[1]
- A dim screen is first a matter for the brightness thumbwheel on the monitor.[3]
The same page prints the expected waveform, with its peak-to-peak amplitude, at each of ten numbered test points on the monitor circuit diagram; use them when scoping the deflection stages.[1]
Disc drive
[edit | edit source]Amstrad's flow chart for the drive (pp. 5–9) works through four checks in order: motor rotation, read error, write error and interchangeability error, with a seek error chart for the second drive only. It is marked "for information only": during the warranty period a faulty mechanism went back to Amstrad.[1]
Soft errors
[edit | edit source]Before blaming the drive, Amstrad has the engineer rule out soft errors, which it attributes to random noise of a few microseconds and to small off-track or write-timing errors:[1]
- Read the track again, ten times or more, until the data is recovered.
- If that fails, step the head to the next track in the same direction and back again.
- Repeat step 1. If the data is still not recovered, the error cannot be corrected.
A write that fails is repeated with a read-back check. If it still fails after more than ten attempts, try another track, then another disc; if the error stays with the drive, the drive is faulty, and if it moves with the disc, the disc is.[1] Seek errors come from the stepper motor or its drive circuit, or wrong carriage torque; recalibrate to track 00 and seek again.[1]
Motor and speed
[edit | edit source]- Motor runs but the disc does not turn: belt.[4]
- Disc turns at the wrong speed: the index period should be 200 ±2 ms, adjusted with VR201 on the drive board after any spindle motor work.[1]
- Low read signal: the head output on track 39 of the EME-CF2 test disc should be at least 140 mV peak to peak between TP1 and TP2. Clean the head and test again; Amstrad replaces the head if it stays low.[1]
Not a fault
[edit | edit source]The drive is not ready until the disc has made two revolutions after it is inserted.[1]
Memory
[edit | edit source]The service manual has no RAM test of its own; Amstrad relied on the R.P.3.[1] The PCW 8256's 256K is eight TMM41257P-15 DRAMs at IC104–IC111 on the CPU board.[1] On a machine that has been upgraded to 512K, check that the eight extra chips sit in IC112–IC119 and that links A–D match Amstrad's memory table: for 256K, A on, B off, C off, D on; for 512K, A off, B on, C off, D on.[1] The RAM disc, drive M:, is made from memory and loses its contents at every reset or power-off; save work to a floppy first.[4]
Keyboard
[edit | edit source]The keyboard has its own controller, the Amstrad 40027 (IC801), with a 5 MHz ceramic resonator (X801), and connects through a coiled DIN cord (CD803) to the 4-pin socket on the right of the monitor unit.[1][3] It sends key data serially, on a data line and a clock line that both idle high.[2] If the keyboard sends a steady stream of data and its Shift Lock LED stays lit, check option link LK1, which puts it into a test mode.[2] A keyboard from another PCW 8256 or 8512 is a direct swap.[4]
Printer
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Printer does not respond | Bail bar forward, no paper, printer off-line or waiting for paper | Put the bail bar back on the platen and load paper. Press PTR to enter Printer Control State and check the printer is on-line. Switch off and check both printer cables.[3] |
| Printer runs but nothing appears on the paper | No ribbon cassette | Fit a ribbon cassette.[3] |
| Paper jams | – | Press PTR to halt printing, pull the bail bar forward or turn the paper loading knob a quarter turn towards you, and clear the paper.[3] |
| Paper does not autoload | Paper pushed in too far | Rest the paper in the guide and let the printer take it.[3] |
| Light or smeared print | Wrong print head lever setting | Use position 2 for a single sheet of ordinary paper.[3] |
The printer's driver board (MS0030B) carries an NE556 (IC702), two CD4503s, a CD40106, a CD4094 and two HA13408 driver ICs (IC706, IC708); the printer control logic is the Amstrad 40026 (IC701) on the CPU board.[1] Amstrad supplied complete printer mechanisms on exchange and advised engineers to exchange the mechanism unless the problem was straightforward.[1]
Related pages
[edit | edit source]- Amstrad PCW 8256 · Amstrad PCW 8256 Maintenance Guide · Amstrad PCW 8256 Capacitor Replacement Guide
- Amstrad PCW 8512 Troubleshooting Guide · Amstrad PCW 9256 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 1.15 1.16 1.17 1.18 1.19 1.20 Amstrad, PCW 8256/8512 Personal Computer Word Processor Service Manual. Hosted as File:Amstrad PCW 8000 Series Service Manual.pdf, described at Amstrad PCW 8256 / PCW 8512 Service Manual. Notes to service engineers p. 3; software errors p. 4; drive diagnostic flow charts pp. 5–9; drive mechanical replacements p. 10; drive alignment checks pp. 11–14; monitor alignment chart p. 17; cabinet parts list p. 23 (PDF p. 24); electrical parts lists pp. 33–34 (PDF pp. 34–35); memory options table (PDF p. 36).
- ↑ 2.0 2.1 2.2 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 10.2 (keyboard links), section 10.4 (keyboard connection and wire protocol).
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 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. Chapter 1, pp. 1–8; Appendix I, Troubleshooting, pp. 141–143; Appendix II, pp. 145–148.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 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. Community advice: boot behaviour with and without a disc, the perished drive belt as the most common fault and its symptoms, the RAM disc M: being lost at reset, interchangeable keyboards.