Amstrad PC7386SX Troubleshooting Guide
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Amstrad's service manual for the Amstrad PC7386SX has no fault-finding chart. The checks below are built from its circuit diagrams, PCB view and parts list, with owner reports from the Vogons forum for hard disc problems.[1] The same board is used in the Amstrad Mega PC; the Amstrad Mega PC Troubleshooting Guide adds the games card and the PC14DSM monitor.
Power
[edit | edit source]The supply module connects to the main board through the 12-pin header CON1.[1]
| Pin | Signal |
|---|---|
| 1 | Power Good (PWGOOD) |
| 2, 10, 11, 12 | +5 V |
| 3 | +12 V |
| 4 | −12 V |
| 5, 6, 7, 8 | Ground |
| 9 | −5 V |
Amstrad rates the supply at 50 W.[1] The Mega PC uses the same module (part 273888), and the rating label on a Mega PC gives +5 V at 7.5 A, +12 V at 2 A, −12 V at 0.2 A and −5 V at 0.1 A.[2][3]
| Symptom | Probable cause | Action |
|---|---|---|
| Dead, no lamps | Mains lead, rear switch, supply module | Check the mains lead and switch. Measure the rails at CON1 with the board connected; the module is replaced as a unit (273888) |
| Power lamp lit but no start | Missing rail, Power Good absent, a short on a card or drive | Measure +5 V on pins 2 and 10–12 and Power Good on pin 1. Remove the expansion cards and unplug the drives, then try again |
| Keyboard and mouse both dead | F1 open | F1 is a 2 A fuse resistor (BEL 2A MQ, 273945) feeding +5 V to both sockets through L2. Measure +5 V on the sockets and check F1 for continuity |
| Serial ports dead, parallel port working | ±12 V supply to the line drivers, MC1488A (U38, U39) or MC1489A (U40–U42) | Measure +12 V and −12 V at CON1, then at the MC1488A supply pins; D12 and D13 (1N4001) are in the ±12 V feed on schematic 7/13 |
Sources: schematics 1/13 and 7/13 and the parts list.[1]
Setup, clock and battery
[edit | edit source]The real-time clock and setup memory in the WD76C20 (U33) run from a 3.6 V battery through D8 and R26, with C60 (1 µF) on the battery line and an external battery header, J9.[1] A machine that loses the date, the time or the hard disc type at every switch-on has a flat or leaking battery. Replace it and check for corrosion as described in the Amstrad PC7386SX Maintenance Guide.
Hard disc
[edit | edit source]The floppy and IDE interfaces come from the WD76C20, with the IDE data lines buffered by 74LS245s on schematic 6/13.[1] The BIOS has no automatic drive detection: the drive's cylinders, heads and sectors are entered by hand as a user type.[4]
| Symptom | Probable cause | Action |
|---|---|---|
| "Fixed Disk Controller Failure" with a replacement drive or CompactFlash adapter | The on-board interface does not work with that drive | One owner tried drives from 640 MB to 8 GB and CompactFlash adapters and got this message with all of them; an ISA IDE controller in the spare slot solved it. A Mega PC owner got one 20 GB drive working as a user type with 2048 cylinders, 16 heads and 63 sectors (seen as about 500 MB), but other drives gave the same error with those settings[4] |
| DOS installs to a CompactFlash card but the machine stops at a blinking cursor on reboot | BIOS hard disc routines | On a Mega PC, OnTrack Disk Manager on the card fixed booting and allowed a 2 GB or larger card in several partitions; an XT-IDE BIOS on a network card is another route[5] |
| Original drive not found after a battery change | Drive type lost from setup | Re-enter the original drive's parameters in setup; the Mega PC carries a "Hard disk drive type 17" label on the rear[3] |
| Drive spins up, not found, original setup correct | Drive, cable (273926) or interface | Try the drive in another PC and swap the cable; see Hard Drive Maintenance and Repair |
No picture
[edit | edit source]The video section is the WD90C11 VGA controller (U50), video RAM at U51 and U52 (with U53 and U54 as the 512 KB option), the ADV471 RAMDAC (U57) and the ICS1394 clock synthesiser (U55).[1]
| Symptom | Probable cause | Action |
|---|---|---|
| Machine starts (drive activity, beeps) but no picture on any monitor | Video section, monitor lead | Try a known-good VGA monitor and lead. Check +5 V at the video RAM decoupling capacitors C110 and C111, and the RAMDAC analogue supply at C137 |
| Picture lost after fitting the video RAM upgrade | Wrong or misfitted chips at U53, U54 | Remove the added chips. Check the type against the chips at U51 and U52 and the orientation against the top view |
| Colours missing or wrong | RAMDAC (U57) or the VGA lead | Check the lead and the 15-pin socket pins, then the RAMDAC area |
| Picture unstable in some modes only | Clock synthesiser (U55) or its supply | Check C131 and C132 and the 5.1 V zener D14 that feeds the ICS1394 analogue supply |
Sources: schematics 12/13 and 13/13 and the parts list.[1] See the Amstrad PC7386SX Capacitor Replacement Guide for the capacitor values.
Front panel
[edit | edit source]The front panel connects through CON2 (CON11 is wired in parallel). The power lamp is green, the hard disc lamp red and the turbo lamp yellow; the turbo lamp is driven by a 7406 gate (U1) and the speaker by the transistor Q1 (2N2222A).[1]
| Pin | Signal | Pin | Signal |
|---|---|---|---|
| 12 | Ground | 6 | Turbo lamp − |
| 11 | Reset | 5 | Turbo lamp + |
| 10 | Hard disc lamp − | 4 | Ground |
| 9 | Hard disc lamp + | 3 | Power lamp |
| 8 | Speaker + | 2 | Keylock |
| 7 | Speaker − | 1 | Turbo switch |
- Reset button has no effect: the reset line has C3 (10 µF 16 V) and R5 (300 Ω) on schematic 1/13; check the button, the cable and C3.[1]
- No speaker sound: check the volume control on the rear panel (DE-9, 500 Ω), the speaker (DE-10) and Q1.[1]
Related pages
[edit | edit source]- Amstrad PC7386SX · Amstrad PC7386SX Maintenance Guide · Amstrad PC7386SX Capacitor Replacement Guide
- Amstrad Mega PC Troubleshooting Guide · Hard Drive Maintenance and Repair · Floppy Drive 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 1.10 Amstrad plc, PC7386SX Personal Colour Computer Service Manual, first published October 1992. Hosted as File:Amstrad PC7386SX Service Manual.pdf, described at Amstrad PC7386SX Service Manual. Technical specification p. 2; main PCB top view p. 3; schematic diagrams 1/13 (power header, front panel, keyboard and mouse, p. 5), 6/13 (floppy, IDE, battery, p. 10), 7/13 (serial and parallel, p. 11), 11/13–13/13 (video, pp. 15–17); parts lists p. 19.
- ↑ Amstrad plc, MEGAPC3H40 with Games Card / PC14DSM 14" Dual Synch Colour Monitor Service Manual. Hosted as File:Amstrad Mega PC Service Manual.pdf, described at Amstrad Mega PC Service Manual. Parts list (p. 4): power supply 273888.
- ↑ 3.0 3.1 Bungle, "MegaPC Rear.jpg", Wikimedia Commons, 2007 (public domain). Retrieved 2026-10-02. Rating label of a Mega PC.
- ↑ 4.0 4.1 Vogons forum, "Amstrad PC7386SX Hard Drive issues". Retrieved 2026-10-02. A PC7386SX board owner and a Mega PC owner on BIOS drive types, the "Fixed Disk Controller Failure" message and an ISA controller as the fix.
- ↑ Vogons forum, "Amstrad 386 PC won't boot from compact flash but WILL install to it". Retrieved 2026-10-02. A Mega PC (PC7386SX board) with a 512 MB CompactFlash card; OnTrack Disk Manager and XT-IDE suggested by another owner.
