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Bruce W...1
 
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Default Astron VS-35M power supply broken

My Astron VS-35M power supply (http://www.astroncorp.com/linear.shtml)
isn't working right. Unable to get support from Astron I'm hoping
someone here can help me fix it. I'd really hate to ship it to
California, this thing must weigh 30 lbs..

Here is a symptom of the problem:
When the power supply is set at 13V and the current knob at zero, on
connecting it to a 3-ohm power resistor the current goes to 2 amps and
the voltage drops to 6V. When the current knob is then set to full, the
voltage returns to 13V and the current goes to 4 amps (should be 35A).

Here's voltages I measured on the LM723 voltage regulator:
[No load voltages]
Pin Voltage
2 13.69
3 13.26
4 6.38
5 6.38
6 7.18
7 0
10 14.25
11 29.33
12 29.31
13 15.51

Here's the schematic for the power supply:
http://www.didah.com/astron/circuit.gif
And here's the data sheet on the voltage regulator:
http://www.didah.com/astron/LM723.pdf

I'm no electronics expert (or I probably could have fixed it). But I am
good with a soldering iron and have lots of test equipment. Any
suggestions on what to look at?

Thanks for your help.