Editing IBM PC XT Maintenance Guide (section)

== Quick-Fix Flowcharts ==

=== No power, fan dead ===
* Confirm mains lead and rear-panel switch.
* Disconnect P8/P9 from the motherboard. With P8/P9 unloaded, does the PSU fan spin and the rails read correctly?
** If yes: there is a short on the motherboard or an ISA card. Suspect '''C56''' first (+12 V short). Then remove all ISA cards and reconnect P8/P9; if the PSU then runs, the fault is on a card.
** If no: the PSU itself is faulty.

=== Dead machine, fan runs, no beep ===
* Probe the &minus;5 V rail.
* Reseat U18, U19, the 8088, and all bank-0 RAM.
* Piggyback known-good RAM onto each bank-0 chip in turn.
* On the 1986 BIOSes, a failed U19 produces a silent dead board (unlike the 1982 BIOSes which fall back to "F6000 ROM").

=== "1701" hard disk error at POST ===
* Reseat the [[IBM Fixed Disk Adapter|Fixed Disk Adapter]] card.
* Reseat the 34-pin control and 20-pin data ribbons at both ends.
* Verify +12 V at the HDD power connector under load.
* Listen for the spindle motor. If it does not spin, try a careful manual rotation to free a stuck head.