Batboard

I have a Motorola rack mount repeater power supply. The cont. duty one with the built in battery charger.
There is an internal 20 amp glass fuse that blows as soon as power is applied with no load connected. No obvious signs of damage, all the external fuses are good.
Does anyone have any ideas or experience with this problem.

Thanks, Squelch

Hi:

Well, unfortunitely you could have a Easy
Problem or a Nightmare. I have fixed many
of these Power Supplies, and its not a easy
task all the time.

You could most likely have a " Filter Cap "
that is Shorted, and since they are all in
Parallel, you might have a problem finding
" Which " one is bad.

Also, Regulators Fail, Diode Blocks, and
in rare cases, the Transformer goes. Service
Tech that address these issues have a complete replacement Power Supply on stand-by,so if one goes, they just replace the PS
in question, take the other back to the shop
for a bench repair.

I have a few of these if you are interested

Not super cheap, but inexpensive in relation
to Motorola's price.

Warranteed too !

Monty

What you might try doing is to isolate the problem. Lift the load off of the power supply and try it. If the fuse still blows, then remove all the connections from the output of the diode stack. If the fuse still blows, then the diode stack is bad or the transformer. Next lift the input to the diode stack. If the fuse still blows, guess what, need a new transformer.

Might also check to see if there is any MOV protectors on the AC input. If you took a power surge, this may be the cause of your problem.

Jim

If one of the pass transistors fail (short) the crowbar scr kicks in and shorts the power supply 13 volt out put line as a safety measure for overvoltage and blows the 20 amp fuse. Happens all the time if the tempature is elevated and the transistors get too hot because they were not correctly heat sunk, loose on the heatsink, or have a poor application of heat transfer compound.