Amstrad PC1512 Troubleshooting Guide
The Amstrad PC1512 takes its power from the monitor, so a dead machine is diagnosed from the monitor's supply first, then through the BIOS self-test messages and the drives. Amstrad's own service route for the computer was its RP4 diagnostic card or diagnostic disc, which the service manual mentions but does not document; the manual's fault-finding flow charts cover only the floppy drive.[1] The self-test messages below come from the Technical Reference Manual. Procedures are in the Amstrad PC1512 Maintenance Guide.
The power-on self-test
[edit | edit source]At switch-on the BIOS checks its ROM checksum and tests the display memory and controller, then shows "Please wait" on the top line and adds a dot as each further test starts. A failure stops the machine with an error message, except the keyboard test, which repeats until it passes and sounds a short beep every five seconds while it waits.[2]
| Order | Test | Error reported (the manual's description) |
|---|---|---|
| 1 | ROM checksum | Faulty ROM checksum |
| 2 | Display RAM and 6845-compatible controller (before "Please wait") | Faulty VDU |
| 3 | 8237 DMA controller | Faulty DMA |
| 4 | 8253 interval timer | Interval timer error |
| 5 | 8255-type status ports | Faulty real time clock (as printed in the manual) |
| 6 | HD146818 real-time clock counting and NVR | Faulty real time clock |
| 7 | 8250 serial port, in loop-back mode | Faulty system serial port |
| 8 | Parallel port data latch | Faulty printer port |
| 9 | Mouse X and Y counters | Faulty mouse coordinate register |
| 10 | System RAM | Faulty RAM |
| 11 | 8259 interrupt controller | Faulty interrupt controller |
| 12 | Floppy drives: each head is stepped to track 10 | Floppy disk controller error |
| 13 | Keyboard processor, which must return AAh | Keyboard error (repeats until it passes) |
Count the dots before the machine stops to find the failing test. After a soft reset (Ctrl, Alt and Del) every test runs except the RAM tests.[2] If all three option links LK1–LK3 are fitted, the BIOS runs only the keyboard and disc tests and carries on past a failure in either, which lets a machine with a faulty peripheral be brought up for diagnosis; with the links fitted the BIOS messages stay in English.[2][3] A RAM parity error raises a non-maskable interrupt; the BIOS displays a parity error message and hangs until the machine is switched off.[2]
Power
[edit | edit source]The system unit has no supply. If neither the monitor nor the computer shows any sign of life, start in the monitor.[4]
Check the monitor's 3.15 A time-lag mains fuse first. A blown fuse usually means a shorted part in the supply's primary side, so find it before fitting a new fuse; the supply's parts are listed in the Amstrad PC1512 Capacitor Replacement Guide.[1] With the monitor working and the computer dead, measure the rails at the 14-way DIN plug:
| Pin | Rail | Amstrad setting | Maximum current |
|---|---|---|---|
| 3, 5 | +5 V | 5.10 V ±0.02 V | 7.00 A |
| 11 | +12 V | 12.15 V ±0.02 V | 4.9 A |
| 13 | −5 V | 5 V ±0.05 V (magnitude) | 1 A |
| 9 | −12 V | 12.0 V ±0.05 V (magnitude) | 0.24 A |
| 2, 4, 8, 10, 12 | 0 V | – | – |
The settings are Amstrad's adjustment targets from pp. 26–27 of the service manual; the currents are from the Technical Reference Manual.[1][4] The overcurrent protection is set to trip at 4.5 A on the +12 V output, so a hard disc with a seized motor or a faulty expansion card can shut the supply down.[1]
Owners also report PC-MM or PC-CM supplies that make a continuous crackling noise and do not power the computer, and others that cycle on and off.[5]
If the monitor is missing or dead, owners power the system unit from a separate PC supply wired to this pinout and drive a different display from an add-in card; the PC1512's own display adaptor cannot be disabled.[6][7]
Display
[edit | edit source]The PC-MM and PC-CM take a combined sync signal on pin 1 of the 8-way DIN video plug, with intensity, red, green, blue and a "black" line on the other pins; they are not standard CGA monitors.[4][7]
- PC-CM with no picture and a dead supply to the tube: one repairer found the horizontal output transistor, Q410, a 2SD1427 (1500 V, 5 A), shorted. He also reports that the service manual has no schematic for the PC-CM's deflection and EHT circuit, only for its supply, and that the PC-CM board in his machine was a later revision than the one drawn, with components moved and renumbered.[8]
- Picture too dark or blank with sound and drive activity: check the brightness and contrast controls first. A PC1640 owner who had shelved a "dead" ECD for years found it working once these were turned up.[9] Then check the PC-MM cut-off (VR405) and sub-contrast settings or the PC-CM sub-brightness (VR101) settings in the alignment tables.[1]
- Picture rolling or tearing on the PC-CM: horizontal hold is VR402, set to 15.625 kHz at pin 4 of IC402 with VR403 at mid position.[1]
See CRT Discharge Procedure before working on either monitor.
Floppy drives
[edit | edit source]The disc test steps each fitted drive to track 10 and reports a floppy disk controller error if the drive does not respond; it does not check that the head arrived at the right track.[2]
| Symptom | Probable cause | Action |
|---|---|---|
| Floppy disk controller error at start-up | Drive A: missing, unpowered or jumpered as the wrong unit; cable; controller | Check the drive's power plug and that drive A: is set to the first drive select; fit LK1–LK3 to bypass the test while diagnosing |
| Drive light on permanently | Cable fitted the wrong way round | Turn the card-edge connector over |
| Drive seeks but will not read | Dirty heads, sticky head rails, unreliable media | Clean the heads with 91% isopropyl alcohol; see Floppy Drive Repair |
| Replacement drive will not work as A: | Jumpered for an IBM cable | Set it to DS0; the PC1512 cable has no twist |
The drive select and cable notes are from Amstrad owners; the head cleaning from the service manual.[1][10][11] On the PC1640, a floppy controller error that persisted with a good drive was traced to a failed 5.6 Ω fuse resistor, R181, feeding the 74LS125 at IC110 that passes the floppy interrupt; the PC1512 parts list has the same 5.6 Ω fuse resistor at R181 and a 74LS125 at IC110.[11][1] The full repair is in the Amstrad PC1640 Troubleshooting Guide.
Memory
[edit | edit source]- Faulty RAM at start-up: the main memory is eighteen MN41256-15 DRAMs, IC135–IC152.[1]
- Machine reports 512K after a 640K upgrade: check that LK4 has been moved to the right-hand pair of pins and that every upgrade chip is seated the right way round.[12]
- A fault in the upper 128 KB can be isolated by setting LK4 back to 512K.[12]
Clock and configuration
[edit | edit source]- "Please fit new batteries" at start-up: the AA cells are low or missing, and the configuration has been reset to defaults. Fit new cells and run NVR.[4][13]
- Configuration lost although the cells are good: check the leads from the cell tray and the battery sense circuit; the BIOS also resets the NVR whenever its checksum is wrong.[2]
- Clock drifts: the clock crystal is X103 (32.768 kHz) and its trimmer TC101; Amstrad's adjustment uses a timing meter on pin 21 of IC134.[1]
Keyboard and mouse
[edit | edit source]- Keyboard error with a beep every five seconds: the keyboard processor is not returning its self-test code. The keyboard is Amstrad's own design; check its cable and DIN plug and its own board before suspecting the main board.[2]
- Mouse moves but the buttons do nothing: the buttons are read as key codes and need the KEYB program from Amstrad's system discs.[13]
Related pages
[edit | edit source]- Amstrad PC1512 · Amstrad PC1512 Maintenance Guide · Amstrad PC1512 Capacitor Replacement Guide
- Amstrad PC1640 Troubleshooting Guide
- Capacitor Failure Symptoms · CRT Discharge Procedure · Floppy Drive Repair · Hard Drive Maintenance and Repair
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Amstrad plc, PC1512 Personal Computer, PC-MM Monochrome Monitor, PC-CM Colour Monitor Service Manual. Hosted as File:Amstrad PC1512 Service Manual.pdf, described at Amstrad PC1512 Service Manual. Servicing note p. 3; FD-3 flow chart pp. 3–6; electrical parts lists pp. 18–20; alignment instructions pp. 26–27; schematics pp. 30–41.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Amstrad, PC1512 Technical Reference Manual, section 2, transcribed by John Elliott: seasip.info. Retrieved 2026-10-02. Sections 2.1 and 2.2: the self-test order, the error each test reports, the LK1–LK3 bypass, the NVR checksum and the parity error handler.
- ↑ John Elliott, "PC1512 motherboard links", seasip.info, 22 August 2003. Retrieved 2026-10-02. LK1–LK3 language and diagnostic mode, LK4 memory size, LK5 ROM size, LK6–LK7 character set, LK8 floppy READY line.
- ↑ 4.0 4.1 4.2 4.3 Amstrad, PC1512 Technical Reference Manual, section 1, transcribed by John Elliott: seasip.info. Retrieved 2026-10-02. Section 1.9 (clock and AA cells), 1.20 (video connector) and 1.21 (power connector pinout and current ratings).
- ↑ Phil Saunders and others, "Amstrad Monitor Repair", Vintage Computer Federation Forums, May 2014. Retrieved 2026-10-02. Community report of two faulty PC1512 monitors: one crackling and not powering the base unit, one cycling on and off.
- ↑ JidaiGeki and dr.ido, replies in "Amstrad 1512DD am i in trouble?", VOGONS, May 2019. Retrieved 2026-10-02. Community advice: without the monitor the PC1512 has no power supply; a supply can be wired to the published DIN pinout; the keyboard is the harder part to replace.
- ↑ 7.0 7.1 DOS Days, "Amstrad PC1512 and PC1640". Retrieved 2026-10-02. The 14-pin DIN pinout for powering the system unit from another supply, the PC1512's display adaptor that cannot be disabled, the composite sync of the PC1512 monitors, the non-standard keyboard and mouse.
- ↑ DaIceMan, "Amstrad PC1512 CM (640k) SD repair", VOGONS, 5 June 2026. Retrieved 2026-10-02. Community repair report: PC-CM dead with Q410 (2SD1427) shorted; the PC-CM deflection schematic absent from the service manual; a later PC-CM board revision with changed component numbering.
- ↑ DOS Days, "The Amstrad PC1640 Project – Part 2", 18 August 2026. Retrieved 2026-10-02. A PC-ECD thought dead that worked after the brightness and contrast were turned up; memory parity errors and hangs on the original main board.
- ↑ John Elliott and others, "Amstrad PC1512", Vintage Computer Federation Forums, July 2011. Retrieved 2026-10-02. Community reports: floppy cable soldered to the board, drives selected by jumper, 1.44 MB drives as B:.
- ↑ 11.0 11.1 jarcher1701, Deunan, austfox, modem7 and others, "Amstrad PC1640 – Faulty Floppy Disk Controller or Disk Drive", Vintage Computer Federation Forums, October–December 2023; also VOGONS t=96798. Retrieved 2026-10-02. Community repair on the closely related PC1640: a reversed cable lighting the drive LED permanently, the drive needing to be set to drive 0, the LK1–LK3 bypass, and C124 and R181.
- ↑ 12.0 12.1 John Elliott, "Amstrad XTs: Memory Upgrades", seasip.info, 26 June 2019. Retrieved 2026-10-02. Upgrade chips and LK4, and setting LK4 to 512K to isolate a fault in the 512–640K range.
- ↑ 13.0 13.1 John Elliott, "Amstrad XTs: Questions and answers", seasip.info, 26 June 2019. Retrieved 2026-10-02. NVR setup program, Amstrad mouse buttons needing Amstrad's KEYB, system discs.