Low Voltage drop at TP1 5V
and TP2 12V while cpu connected to Power supply:

Isolate Power supply from cpu:

Make a dummy load:
Connect a 6V pinball lamp to 5V output on power supply, Normal power will light bulb 60%
while connected check for voltage drop at test pins 1 and 3
No Light? Suspect bad Cap as mentioned C10 and or faulty BR1 bridge rectifier.

Check Fuses 4 and 5 they supply AC to the Bridge rectifier which divides -12V and +12V
Suspect a Bad Rectifier with may have partially shorted internal diodes on the + 12v side
5V cannot be made if less than 12v from BR1 under load is going into the regulator (which also splits off for 12V+ unregulated output) isn't there (Garbage in Garbage out)

TAXI POWER SUPPLY (resized).png

TAXI POWER SUPPLY 1 (resized).png