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Guitar Amp repair / Troubleshooting

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tonymazz

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Greetings everyone ! I am new to this forum and glad I found it....

I am currently working on repairing a small Fender Frontman 15 watt guitar amp. I have been working through the schematic "TP" voltages and noted an anomaly where the voltage does not agree with what should be....

See attached Schematic and powersupply section. TP6 says I should see -14.9 volts DC. The Actual is -2-3 vdc. So does this tell me that there is a shorted component ? i.e. like c12 diode or c32 cap ? All the voltage TP's are good upto that point. TP-1 through TP-5...then TP6 reads this low voltage...

Since I am new to all this...current is inversely propotional to resitance right ?

I just don't know which to replace .....any hints would be most appreciated....


Amp Symptoms: Power up, no LED light, hear a slight pop at power up through speaker, not sound, now response....since no LED lit I am starting at the power supply and working forward.....

Thanks guys
 

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flat5

Member
It's fed voltage from TP4. What voltage do you read at TP4?
If it is ok or close to -23v then yes C32, CR12, R49 should be checked right away.

Your doing well so far :)
 
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tonymazz

New Member
Thanks....I will give the suggestions a try.....

BTW TP4 shows the correct neg DC voltage....moving up the rail shows a much smaller voltage ....
 

tonymazz

New Member
Guitar Amp - FIXED !

After replacing CR12 diode it works !

I learned that pulling one end of the diode out of the circuit..and in checkikng with a vom ...one direction reads ohms and flipping the leads the other read resistance as well...possibly an open diode....so I repalced it and voila I am back in business....

thanks very much for the help and encouragement ...:D
 
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