Fender Super Champ X2 smoking resisitor

[calenk]

Hey there i have a super champ x2 in for repair and r47 was smoking and getting red hot i replaced it and same thing, i tested c40 and c41 and they test good. also i only measure about 3 volts on TP31. any ideas?

[52 Bill]

Pull out the driver tube, does the voltage at TP31 come back up?

[calenk]

Pull out the driver tube, does the voltage at TP31 come back up?

it does the same thing regardless if there is tubes in it. sorry i should have mentioned that.

[52 Bill]

How did you test C41?

There is a short in the inverter node of the power supply. C41 would be the obvious part to cause this, but there could be other causes. Check for shorted connections and or pc board traces, etc.

With the amp off and the caps discharged take a resistance reading from TP31 to ground. What reading do you get?

[calenk]

How did you test C41?

There is a short in the inverter node of the power supply. C41 would be the obvious part to cause this, but there could be other causes. Check for shorted connections and or pc board traces, etc.

With the amp off and the caps discharged take a resistance reading from TP31 to ground. What reading do you get?

i took them out and put them on my capacitance meter and they both tested at 22 uF. im getting 298 ohms from TP31 to ground. is it possible the caps could show proper uF and still be bad?

[52 Bill]

Yes, remove C41 from the circuit and read the resistance from TP31 to ground again and the resistance across C41.

[calenk]

Yes, remove C41 from the circuit and read the resistance from TP31 to ground again and the resistance across C41.

with c41 out im getting 1.1 M to ground but it never really stabilzes, i tried a new 22 uF cap with no difference

[52 Bill]

with c41 out im getting 1.1 M to ground but it never really stabilzes, i tried a new 22 uF cap with no difference

1.1M from TP31 to ground or across the cap out of circuit?

[calenk]

1.1M from TP31 to ground or across the cap out of circuit?

Sorry that's from TP31 to ground, across the cap was something like 218 M

[52 Bill]

The readings don't make any sense to me, where did the earlier 298 ohms go? Is the voltage back at TP31? Was there a shorted connection on C41?

If R47 is burning and the voltage at TP31 is 3 volts dc, something is loading the circuit down. As I said before C41 is the most likely suspect, but there are other possibilities as well.

Did you replace R47? What does its' resistance read?

[calenk]

The readings don't make any sense to me, where did the earlier 298 ohms go? Is the voltage back at TP31? Was there a shorted connection on C41?

If R47 is burning and the voltage at TP31 is 3 volts dc, something is loading the circuit down. As I said before C41 is the most likely suspect, but there are other possibilities as well.

Did you replace R47? What does its' resistance read?

i know the readings are all over the place. k i took the board out and removed c41 and r47 and im get 1.2k to ground from TP31. ive tried a new cap and resistor but the voltage at TP31 still isnt coming back.

[The Dude]

Possibly the cap WAS leaky and R79 has also gone towards open? Check the resistor R79. Also check the voltage on both sides of R47 and see if it is indeed still dropping all of that voltage indicating a short down line or if there is low voltage on the supply side of it. You may have only solved part of your problem.

[calenk]

K i believe i have found the problem as i know have voltage back on TP31
a short on a leg of R12. Thanks so much for all your help and quick responses 52 Bill. im gonna toss it all back together and give it a test.

[The Dude]

Glad you found the little bugger!