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Author Topic: Things that would cause a Bridge rectifier to short out??  (Read 129 times)

NPreston

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Things that would cause a Bridge rectifier to short out??
« on: February 26, 2019, 12:31:46 PM »
I have a Yorkville Bloc250 Bass Amp that I am attempting to fix.  It blows fuses upon power up.  I have determined that the bridge rectifier is shorted out..  I am just curious if anyone has any idea what might cause one of these to go before I simply replace it and maybe cook another one?

I have not replaced the rectifier yet, nor have I attempted to power anything in this amp and look for "warm spots" using a bench supply.  I don't have a schematic on hand to post at the moment (just a paper copy stuck on the amp itself), but one thing I did notice, was from the main supply there are a couple power resistors which I believe feed the Power rails for the preamp.  One of these had a bad solder joint, and the PCB directly under looked a bit darkened suggesting maybe it heated up..   

In any case, being that the pre-amp is mostly op amp stages requiring dual rails, could it be possible that if one power rail was out, that the op amp(s) in the signal chain just max out to one power rail, therby hammering the power amp with DC and therefore asking too much of the Main DC supply??   Just a theory..   

g1

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Re: Things that would cause a Bridge rectifier to short out??
« Reply #1 on: February 26, 2019, 02:31:22 PM »
  Did you remove the bridge rect. to test it?
If not, you may be reading a shorted power transistor across the supply rail.
Shorted power transistor would be the most likely suspect, and this model can be very difficult to repair if that is the case.
How many power transistors are fitted and what type?

NPreston

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Re: Things that would cause a Bridge rectifier to short out??
« Reply #2 on: February 26, 2019, 03:07:51 PM »
I did remove the rectifier..  3 pins out of 4 appear to be shorted together (about 1.5 ohms)  I suspected  output transistors at first, but was able to isolate them by removing fuses that connect the power supply to the output transistors..  and the short appeared on the power supply side..

Enzo

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Re: Things that would cause a Bridge rectifier to short out??
« Reply #3 on: February 26, 2019, 06:31:33 PM »
Don't put too much thought into it.  Something could have caused it to fail, then again, any part can fail on its own.

 

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