[ IBM 5150 with IBM 63 watt power supply. ]



So:
* The power supply's fan does not turn when only the Tandon full-height floppy drive is attached, and
* The power supply's fan does not turn when only the motherboard P9 (+/- 5 volts) connector is attached.

Both of those loads are known to be sufficient on their own to operate the IBM 63 watt power supply in a 5150.


CONCLUSION:  The IBM 63 watt power supply is faulty.