power supply hangup

[JS]

Many years back I made a power supply in Jr. college and have started to use it for some microcontroller work. It uses the LM723 regulator with a pass transistor with a 0 to 25 volt output and it works fine 99% of the time. Sometimes when first turned on the output voltage will go to max, with the output control turned down to zero? I have to shut down and restart to clear the problem. Ideas please? Thanks, JS

[Ron H]

Can you point to a schematic?

[Chris Smith]

I prefere the Lm-317. Simple

[dyarker]

Hard to tell without schematic. Sounds like potentiameter wiper goes open when turned down HARD. Or if LM723 is in socket, one pin is dirty.<p>C U L

[Edd]

JS:You have already received 2 very likely faults from Dale. In case you still don't have a reference '723 schematic at hand, this should suffice, although it should be quite a leap in current capability.
http://www.seits.org/features/pwrsup.gif
(Astron '723 PS ckt)
You might try to replicate the fault by tapping the chassis/ PCB with a screwdrivers plastic handle to check for a loose connection or marginal solder joint. You would want to be monitoring the 723's voltage reference input at pin 4 or its output to the pass xstrs at pin 10 while doing this.<p>73's de Edd
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[JS]

Thanks all for the help, still trying to dig up the schematic.I may have to draw the circuit by hand. Will try your suggestions.JS

[chris_elrod]

Im sure you are aware of how a VR works! It tries to balance a voltage ratio between the output and the reference pins. Check to see that your circuit doesnt have a possiblity for high resistance between these two pins at startup, possibly through a transistor or another device or like the other guys said a bad connection!