My hot rod has distortion problems. When the distortion is off, the yellow distortion light shows up (intermittently) and the sound is not right (neither clean nor distortion) When I turn the distortion on, it switches back off (light turns yellow) when I play any amount of sound at all through it. When the clean channel is on, and the yellow distortion light does not turn on, sometimes the red distortion light comes on, but very faintly and intermittently. But when this happens, the sound does not change other than buzzing or loose connection sound. This is not a connection problem with the pedal or cord (i.e. outside of the amp), as it does this when the pedal is not plugged in too.I don't see any obvious signs of burnt capacitors or loose connections on the circuit board. Help!
There are many components in the system. Electrolytic capacitors are most suspect. C49, C50, C45, C51
There are many others but these are top suspects. You MAY be able to detect a change by cooling these components with circuit cooler spray.
ALSO check the +/- 16 volt power sources in the unit.
Testimonial: "I haven't fixed the problem yet, there is more to it now that I have pinpointed the general problem, but he was right on the mark."
Thank you very much, that helps. I looked closer at the circuit board, and it appears to be burn out around the /- volt power source. So I think that you were right.
The source of the problem seems to be the two 470w 5w resistors where the power sources come in. But when I check them with the multimeter, one of them reads about 480 and the other reads about 490. I would have expected them to be less resistance, or no signal, if anything. The problem is not my multimeter. Other than the circuit board, there the resistors don't appear to be damaged.
Now, one of the circuits on the actual circuit board may have been burnt out (i am not getting a signal through it). I can repair that, and that may be what is causing the amp to cut out. But then, what is causing the resistors to heat up so much in the first place?
I had the same problem probably 5 or 6 years ago, and I took it in to be repaired. The repairman replaced my tubes and did some work on the circuit board. For all I know, the burnt out spot on the board could be from that first time, at least some of it.
Should I replace the tubes? Do they wear out that fast? I have read that bad tubes will cause those 16v resistors to get hot.
Is there supposed to be that much variance in the 470 ohms 5w resistors, or are they damaged?
Now there are 2 zener diodes in the circuit which are right next to those 2 resistors which also appear to be burnt at least on the board. I have not checked those yet.
Should I replace the zeners, the resistors, the tubes, AND the broken circuit on the board, or is that more than is needed?
Any advice or help would be appreciated. Thank you very much.
Resistors have a tolerance and readings of 480 or 490 is acceptable limits
Where board is burned, look for bad soldering. The 470 ohm screen resistors will run hot and may discolor the circuit board.
For the intermittent distortion light I suspect the switch that is a part of the footswitch jack may have poor intermitent contacts.
Plug a low resistance device (like a speaker) or 1/4 inch rod into the footswitch jack to make a firm contact and see if distortion light still changes intermittenly...
Capacitors C49 and C50 are also suspect. Both ar 22mfd/25v electrolytic capacitors.
The 480 resistors commonly get hot and burn the board on the fender hot rods. What can solve that problem (of the board getting burnt) is to raise the 480 resistors off the board by using resistors that have longer wires coming out of the sides..
The problem on my amp was not the power source however, but in the foot switch circuit. It was not the pedal. There was a loose connection on the LED light which tells if the distortion is on (red), light distortion (yellow), or clean (no light). I resoldered the connection and it fixed it.
Thanks for the help all the same.
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