Editing Amstrad PC7386SX Troubleshooting Guide (section)

== Power ==

The supply module connects to the main board through the 12-pin header CON1.<ref name="sm7386" />

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''CON1 power header (schematic 1/13)'''
! Pin !! Signal
|-
| 1 || Power Good (PWGOOD)
|-
| 2, 10, 11, 12 || +5&nbsp;V
|-
| 3 || +12&nbsp;V
|-
| 4 || −12&nbsp;V
|-
| 5, 6, 7, 8 || Ground
|-
| 9 || −5&nbsp;V
|}

Amstrad rates the supply at 50&nbsp;W.<ref name="sm7386" /> The Mega PC uses the same module (part 273888), and the rating label on a Mega PC gives +5&nbsp;V at 7.5&nbsp;A, +12&nbsp;V at 2&nbsp;A, −12&nbsp;V at 0.2&nbsp;A and −5&nbsp;V at 0.1&nbsp;A.<ref name="smmpc">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.</ref><ref name="rearphoto">Bungle, [https://commons.wikimedia.org/wiki/File:MegaPC_Rear.jpg "MegaPC Rear.jpg"], Wikimedia Commons, 2007 (public domain). Retrieved 2026-10-02. Rating label of a Mega PC.</ref>

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Power faults'''
! 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&nbsp;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&nbsp;A fuse resistor (BEL 2A MQ, 273945) feeding +5&nbsp;V to both sockets through L2. Measure +5&nbsp;V on the sockets and check F1 for continuity
|-
| Serial ports dead, parallel port working || ±12&nbsp;V supply to the line drivers, MC1488A (U38, U39) or MC1489A (U40–U42) || Measure +12&nbsp;V and −12&nbsp;V at CON1, then at the MC1488A supply pins; D12 and D13 (1N4001) are in the ±12&nbsp;V feed on schematic 7/13
|}

Sources: schematics 1/13 and 7/13 and the parts list.<ref name="sm7386" />