HP power supply E3616A does not adjust to 0V

[prutser]

I have an HP E3616A power supply which does not adjust down to 0V.  ( somwtimes

Initially I expected some negative voltages being not present or too low, but this is not the case.
It is also not the voltage potmeter. Initially when I switch it on it remained around 3..4V Now after a while it's around 200-300mV
so it might be temperature related. 

Before I start digging further, by coincidence someone who experienced this problem ?

[Stray Electron]

   I have no experience with the E3616 but the E3631A has KNOWN issues with bad ICs and bad resistors and there are some repair threads on this forum.

[prutser]

Thanks for the reply, I checked it, unfortunately it seems a completely different model, so I will start digging 

[fmashockie]

I just fixed a HP E3612A which is slightly different than the E3616A.  I have attached a service manual for this power supply below.  It provides a schematic and a bunch of troubleshooting tips and procedures to try.  If you are getting only high output voltage, it could be a problem with the series pass transistors (Q1 and Q4).  Or there's potentially something wrong with the preregulator SCR circuit.

The issue with my E3612A had to do with current control.  It would always limit the current to 60mA even when set to the higher settings (0.25A and 0.5A).  The problem was a shorted 2N2222A transistor in the series pass circuit. 

Also, always check the snap action button switches on old test equipment (not sure if yours has these but mine is from the early 90s).  They easily get dirty and can create all kinds of weird symptoms.  Just spray some contact cleaner into the top of the switches (or wherever you can get it to penetrate) and press them several times to clean the internal contacts. 

Hope this helps!

[Stray Electron]

    Thanks for posting that fmashockie.  I've added it to my manual collection.