Check The Operating Temperature; Inspect The Motherboard - HP 8753E Service Manual

Check the Operating Temperature

The temperature sensing circuitry inside the Al5 preregulator may be shutting
down the supply. Make sure the temperature of the open air operating
environment does not exceed 55 OC (131 OF'), and that the analyzer fan is
operating.
If the fan does not seem to be operating correctly, refer to "Pan
q
Troubleshooting" at the end of this procedure.
If there does not appear to be a temperature problem, it is likely that Al5 is
q
faulty.

Inspect the Motherboard

If the red LED is still on after replacement or repair of A15, switch off the
analyzer and inspect the motherboard for solder bridges and other noticeable
defects. Use an ohmmeter to check for shorts The +5 VD, +5 VCPU, or
end of this chapter and troubleshoot these suspected power supply lines on the
Power Supply Troubleshooting