Problems with IBM external floppy drive power supply (for Trackstar 128/Apple II application)

["Frank Townsend" <ftownsen@iamdigex.net>]

I've been trying to get my Trackstar 128 going with an IBM PS/2 Model 30
(8086) and have run into a problem that I thought some of the power supply
experts her might be able to help me with.

The PS/2 uses a 360k external floppy drive model 4869-001 which has its own
on-board power supply.  The drive has its own on-off switch.

When the drive is powered on, the light flickers and goes off.  When
switched off, the light flickers and the platter turns slightly.

The IBM Setup Diskette detects two drives some, but not all of the time.
Trying to access Drive A: or B: accesses only the internal 3.5 drive: no
light or drive noises from B:

I took the external drive apart and checked voltages on the drives logic
board on the 12 and 5 Vdc lines at the power supply connector.  When the
unit is first powered on, I get 12 and 5 Vdc.  After about 30 seconds, the
levels begin to fall rapidly until both are at 0.  Powering off and back on
restores the proper voltages.

Is this normal behavior for any PC power supply or a failure mode?