Guitar Amp repair / Troubleshooting

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

It's a short on the -15V rail, could be anywhere on the rail, but most common would be CR12 the 15V zener.

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

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 ....

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 ...

tonymazz said:

After replacing CR12 diode it works !

Click to expand...

Told you - it's ALWAYS the zener that goes S/C.