[ 1. The PSU fan is not turning.
  2. The +/- 12 volt lines on the motherboard are not on their own the cause of the PSU fan not running (but could be a second problem - multiple shorted caps). ]



The P8 plug you removed supplies the +12 and -12 volts to the motherboard.

Because the power supply fan still isn't turning (continuously), the possibilities are now:
* Faulty power supply.
* Motherboard faulty in the way of a short-circuit on the +5 or -5 volt rails.


What Now?

At this stage, it may seem logical to you to remove P9 from the motherboard, in order to see if the power supply fan then turns (continuously)
Unfortunately that logic won't work, because the power supply would be unloaded, and it is well known that the IBM power supplies require a certain minimum load in order to operate.

Reinserting P8 (+/- 12 volts) and then removing P9 (+/- 5 volts) won't work as a diagnostic method either, because the +/- 12 volt load of the 5150/5155/5160 motherboard is not enough of a load for the IBM power supply.

Click here if your computer is an IBM 5150 (PC), with genuine IBM 63 watt power supply.

Click here if your computer is an IBM 5155 (Portable PC), with genuine IBM 114 watt power supply.

Click here if your computer is an IBM 5160 (XT), with genuine IBM 130 watt power supply.