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Astron RM-50M problem

Posted: Mon Aug 25, 2008 5:10 pm
by 007
*x-post from the 'lab*

I got a free Astron 50A linear 12V supply that blows it's 120V fuse at power-up. There is nothing connected to the supply, so this is an internal problem. I know these supplies aren't the best, but it was free because of the I am willing to spend some time and money to fix it.

I looked at repeater-builder, which makes mention of a failed diode bridge rectifier in 35A model, but I don't see these in the 50A model. What else should I be looking at for the failure point?

Re: Astron RM-50M problem

Posted: Tue Aug 26, 2008 12:09 am
by ka7wnf
I have a Vista XXR 20 amp that did that. Turned out one of the power transistors mounted on the external heat sink was bad. It had a dead short. Blew the fuse.

Re: Astron RM-50M problem

Posted: Tue Aug 26, 2008 7:13 pm
by Oldford
That's not really that bad of a supply. I've fixed quite a few over the years, and yes, the bridge rectifier can short out. It is much more likely that the pass transistor(s) is shorted. You can check them by removing them and "ohmming" them out.
Caution: if you have had the thing plugged in, the large filter cap stores a healthy charge. Discharge it with something other than your fingers. If you need a schematic, you can use almost any Astron drawing, as (if I recall) they just use more pass transistors for more amps.

Good Luck, Eric

A Simple Fix

Posted: Sat Aug 30, 2008 8:44 am
by Bat2way
There are 2 chassis mounted rectifiers CR101,102 (1N1184A)(crosses to a NTE5982) which could be shorted out. As Oldford said, also check CR1,CR2 the square pseudo-bridge as I call it, for shorts.

I've had the rear AC socket vaporized by lightning on one of mine, and was easily repairable, so don't worry about these supplies, you got a real deal.

Re: Astron RM-50M problem

Posted: Fri Oct 08, 2010 7:37 am
by jim202
I have also seen the output post short to the chassis. Sometimes they get over tightened and this causes the problem. It is easy to lift the wires from
these output terminals and see what happens.