Troubleshooting super old HP 6203B linear power supply.

[ftransform]

So I got this old linear power supply on ebay a while back. It has worked well for me but it has recently broken.
I have possibly broken it due to stupidity. I shorted out the leads several times in succession in order to watch the indicator needle dance around after a beer (analog gauges amuse me! ). Anyhow the next day I noticed that the power supply was acting a bit funny.

It used to go up to about 9.5 volts (even though it is rated at 7.5V), now it goes up to maybe 7.95 volts. Also prior to this incident when you turned the current adjust knob all the way down while it was set to voltage indication mode the needle would sharply drop to 0, now it slowly drops down to 0.


Another issue is that previously you could set to current knob to like 10mA and the voltage could be raised to 9V. Now you need to set the current knob to like 1 amp before the voltage can reach to its new ~8v maximum.

Furthermore when the meter is set to current mode it shows a small current even when the knobs are turned down, I don't think it used to do this. This leads me to believe that something is shorted?

I have looked at the manual some and taken the instrument apart but I am a bit intimidated. The only thing I have measured so far is the turn pots, and I have noticed a discrepancy between the two knobs, labeled as identical parts in the manual. Using my radio shack digital multimeter I found that the resistance across one pot like 1.45kohms and the resistance across the other pot starts at 1.45kohms but slowly rises to ~1.58 kohms. I'm pretty sure you are not supposed to measure resistance in circuit so I am not sure if this is significant.. I don't really understand why the resistance slowly changes.

Anyway before I start desoldering pots and transistors and all that I thought I'd ask because people on this forum have a ton of experience and maybe I can be pinpointed to the possible issue.

Again I'm not sure if shorting the power supply out 10 times caused it to fail... I figured it would be built to withstand that kind of thing but it is ancient after all.
All the metal is heavily oxidized but the solder joints look great.

Here is the manual for reference:
http://cp.literature.agilent.com/litweb/pdf/06203-90001.pdf

[qno]

Hi,

You are right, this should not have killed the power supply.

There is a trouble shooting procedure in the manual.
Maybe try the calibration procedure first. There you will be pointed to the problem.
There are lots of forums that discuss repairing old HP equipment.

I have a 6253A that has never failed me. Only the potmeters get a little crackly. I have to twist the knob a few times to adjust the voltage or current in detail.