[Test-Equipment] HP 85662A Power supply problems.

[John Kolb]

In multi-output power supplies, it's common for one section to serve 
as the reference
for the other sections - if that one has ripple, the others will follow it.

If the reference supply is not regulating, a load on the output would 
likely lower it's output.
Loading each output, one at a time, and watching all outputs, might 
allow you to
determine which section is the reference, and thus the one to be 
troubleshot first.

John

At 04:47 PM 4/15/2010, you wrote:
>Greetings;
>
>Anyone on the list have experience with the power supply in this unit?
>
>I'm having some real difficulties troubleshooting this unit.
>
>All the supplies are present (+15,-15, HV, etc.) but all show more than
>5 volts of ripple at the test points, the same as that appearing across
>the filter capacitors.
>
>They will not regulate! When I bring the unit up on a variac the
>voltages rise to their nominal values at an input voltage of app. 70
>VAC. When I increase the input the voltages keep climbing and exceed
>their rated values. Above app. 90 VAC the over voltage protector, as it
>should, shuts down the supplies,which are now above their rated values
>(i.e. +15 volts rises to 19 volts).
>
>There was quite bit of power supply damage when I received the unit,
>primarily due to a leaking filter cap on the 140 volt supply. I believe
>all that was corrected, to the point of needed to "grind out" part of
>the PWB where the cap had leaked.