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Astron   ®

If you have had trouble with Astron power supplies blowing fuses, pass transistors, and the 723 voltage regulator chip, on a regular basis, then try this simple remedy:
Put an electrolytic capacitor 200 mf @ 25 volts from the gate to the cathode of the Over Volt Protection SCR. They are usually mounted on the bottom of the cabinet, using a 1/4" stud mount type.

At first I thought this problem to be bad switches, causing such an enormous spike, that it was not being regulated and therefore telling the SCR to "Kill" the AC input fuse. But then, with it happening more and more, it must have put a strain on the various other components.

The 723 voltage regulator can be abused only so much. The output can be shorted many times and all that usually happens is that the supply folds back and takes the drive away from the Pass Transistors. What is really happening when the SCR fires, is, the output of the supply is being forced to Over Current and cause Voltage Foldback, therefore blowing the input fuse. That is why it is very important to stick to the recommended value of fuse.

I will try to find out why Astron's own protection capacitor is not accomplishing what my remedy has. Maybe in the last few years, they have used a lower rated capacitor.

Astron, at times, in certain situations, can be affected by RF. The output can fold back leaving not enough power to run the equipment. This is an easy fix. To cover most RFI, put an .001 cap. across the current limit and the current sense pins of the 723 voltage regulator. These are pin numbers: 2 and 3.

Anyone with more helpful hints, regarding Power Supplies, please drop me an eMail and I will try to post it.

SCR - silicon controlled rectifier
RF - radio frequency
RFI - radio frequency interference

Garrey, KB7KBT

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