HP 6624A overvoltage when disabled

[Vicus]

I try to repair an HP 6624A with 3rd channel that when disabled say overvoltage. If the output is enabled no problem but only if the voltage is set over 1.9V. If the voltage is set under 1.9V the voltage out is clamped to about 0.6V. I try to follow the guide in the service manual without any result. Some idea?

Here the schematic:
http://literature.cdn.keysight.com/litweb/pdf/5989-6871EN.pdf?id=1268102
Here the service manual:
http://ridl.cfd.rit.edu/products/manuals/Agilent/power%20supplies/CD1/Service/6621Aser.pdf

[pelule]

Have you connect the sense line?
/PeLuLe

[Vicus]

Yes, I try also to remove the link and the psu have the same behavior. Only difference is in output precision.

[Vicus]

I found that the two problema (overvoltage when disabled and at low voltage) are the same because disable the output is equal to put the CV at 0V.

The serial number is 3222A07337, no option installed.

I check rail voltage and they are good. Check signal voltage and are ok. Vref ok. DAC ok. Now I need to know how work the rest of the circuit.

[Samogon]

Just in case, check OVP settings.

[rx8pilot]

I have the same unit, very similar problem. Joining the conversation......

Sent from my horrible mobile....