The HP 8600A Problem has Returned

[Penthode]

The voltage across the resistor solely indicates the current flowing. As Kevin said, the regulator feedback is after the resistor so the minor variation of overall output voltage will have little impact.

What I was looking for was as the unit heats up with the lid closed did the voltage across the sensing resistor reach 0.6 volts or where the roll off in output voltage would begin.

If the voltage across the resistor did rise to 0.6v or more, it could suggest the 5v rail current has risen meaning there might be a problem elsewhere. This could exonerate the regulator altogether.