PCB Tracing

SgtWookie

Joined Jul 17, 2007
22,221
OK, so you have a loud hum, and the fuse doesn't blow.

I suggest to you that what happened is that a capacitor went bad, and shorted out. That caused the regulator to overheat and fail shorted, and the fuse to blow.

The failed capacitor is now "open circuit", so it is no longer performing its' function of coupling the AC signal to ground (basically, filtering out the AC) - so you hear lots of ugly noise in the speakers.

You need to find which capacitor(s) have gone bad. Any electrolytic capacitor that is getting power from the 9v supply is suspect.

Much of the time, bad aluminum electrolytic caps will bulge at the top. Sometimes, they corrode out at the bottom, and short-circuit - they LOOK OK, but they are bad. These can be hard to find without test equipment.
 

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
Much of the time, bad aluminum electrolytic caps will bulge at the top. Sometimes, they corrode out at the bottom, and short-circuit - they LOOK OK, but they are bad. These can be hard to find without test equipment.
I tried it but all the capacitors look fine. No signs of bulge or anything burnt.

I forgot to add one info, the short on the circuit is still present. i.e the Vcc and GND line are shorted.
 
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