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Diodes and repairs and questions.

 
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JingleJoe
HG Supreme


Joined: 01 Apr 2009
Posts: 52
Location: England

PostPosted: Wed Jul 21, 2010 12:12 pm    Post subject: Diodes and repairs and questions. Reply with quote

The smell of burnt out diodes is the most horrible smell in the world.

I have been trying to fix my grandad's amplifier for a long time and today I took it apart completely to get a really good look at the circuits. The problem seemed obvious - two bits of PCB trace were broken, it looked like they had burnt through, I soldered wires between the components that were separated by this break and plugged it in ...

Then I smelt something and saw the magic blue smoke rise from the machine Sad Then I smelt something worse.

Two diodes had burnt out and a fuse had blown.

I am still at a loss as to why this happened, should I have left the circuit open? But If I do that then the circuit isn't complete and the amplifier doesn't work!
Previously I thought the problem was the two big filter capacitors on the power supply, they seemed to be not filtering anymore, the broken bits of trace were between the caps and those diodes so I thought "oh the caps were fine it's just the trace" But could my initial suspicion be correct?
Could broken capacitors cause something like this?

I'll post any progress I make but if anyone has any tips or information please feel free to tell me, I will be greatly appreciative of it!
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Fri Jul 30, 2010 10:09 pm    Post subject: Reply with quote

I don't think faulty filter caps would do that. I would look for a high current device that has failed shorted and would pull lots of current through the pulled traces.
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