Editing Amstrad PC1640 Troubleshooting Guide (section)

== Self-test ==

After "Please wait" the BIOS prints a dot as each test starts: ROM checksum, DMA controller, interval timer, status ports, real-time clock, serial port, parallel port, mouse counters, system RAM, interrupt controller, floppy drives and keyboard.<ref name="dd2">DOS Days, [https://www.dosdays.co.uk/topics/amstrad_pc1640_pt2.php "The Amstrad PC1640 Project – Part 2"], 18 August 2026. Retrieved 2026-10-02. The order of the start-up tests and their dots, memory parity errors and hangs that ended in a replacement main board, an ECD that worked once its brightness and contrast were turned up, the floppy controller's lack of high-density support.</ref> A failure stops the machine with a message, except the keyboard test, which repeats. Fitting all three links LK1–LK3, next to IC113, makes the BIOS run only the keyboard and floppy tests and carry on past a failure; with the links fitted a PC1640 reports 512K instead of 640K, which owners have confirmed is normal in this mode.<ref name="vcffdc">jarcher1701, austfox, modem7, davide78, Malc and others, [https://forum.vcfed.org/index.php?threads/amstrad-pc1640-faulty-floppy-disk-controller-or-disk-drive.1245278/ "Amstrad PC1640 – Faulty Floppy Disk Controller or Disk Drive"], Vintage Computer Federation Forums, October–December 2023; first raised on [https://www.vogons.org/viewtopic.php?t=96798 VOGONS]. Retrieved 2026-10-02. Community repair: the "Faulty Floppy Disk Controller or Disk Drive" error, the BIOS disc test, the LK1–LK3 bypass reporting 512K, IC117 and IC118 signal checks, the failed 5.6 Ω fusible resistor R181 feeding IC110, the shorted 100 µF capacitor C124, a blank screen afterwards cured by resetting the DIP switches.</ref><ref name="trm2">Amstrad, ''PC1512 Technical Reference Manual'', section 2.2, transcribed by John Elliott: [https://www.seasip.info/AmstradXT/1512tech/section2.html seasip.info]. Retrieved 2026-10-02. The self-test order and the LK1–LK3 diagnostic mode, shared by the PC1640.</ref>