Editing IBM PC (5150) Maintenance Guide (section)

== Common Failure Points ==

=== Tantalum capacitor short-circuit ===
A short on the +5 V or +12 V rail of the motherboard caused by a failed tantalum capacitor is the single most documented 5150 fault. The fan may still spin while the PSU's overcurrent protection latches the rails off. Both [https://www.minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_5volts.htm minuszerodegrees.net's +5 V short-circuit guide] and the [https://minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_12volts.htm +12 V short-circuit guide] document the affected positions per motherboard revision.

=== Bank 0 RAM dead ===
A failed chip in bank 0 produces a silent "dead" motherboard. Vintage RAM has a relatively high failure rate. Piggyback known-good 4116 (early board) or 4164 (later board) chips one position at a time to isolate the failure.

=== Floppy drives ===
The [[Tandon TM100-2]] / TM100-2A needs a belt change every decade or so, and the head-positioner lubricant hardens over time. Clean with isopropyl alcohol; re-lubricate sparingly with white lithium grease.

=== Keyboard ===
* The Model F's foam-and-foil pads degrade with age, producing dead or stuck keys. See [[IBM Model F (83-key)#Foam Pad Repair|Foam Pad Repair]].
* The DIN-5 cable develops broken conductors at the strain relief; symptom is a 301 / intermittent dead keyboard.