Problem with my Fender Hot Rod Deluxe

[guitkrazy]

I am a newbie here, I have a Fender Hot Rod Deluxe and for some reason I have lost almost all of its power. Meaning in both cannel I have the volumes maxed and it is hardly hearable. I first replaced all of the tubes (Pre & Power) and it did not correct the problem. I then feared it may've been a blown output tranny I had one from another fender amp that was good- I put it in and still did not correct the issue. So I probed the board looking for anything out of the ordinary. The heat coming off of the 2 ceramic resistors was extreme even at first turning on. I noticed on the backside of the board where the solder is a big burn area in around the super hot resistors. Then I checked one of the diodes and that appeared blown; so I replaced that thinking it may solve my problem. No luck! I am really getting frustrated with this amp. Now the channels will not even switch! Any ideas or help will be greatly appreciated! Uggh! Thanks!

[52 Bill]

Welcome.

Then I checked one of the diodes and that appeared blown; so I replaced that thinking it may solve my problem. No luck! I am really getting frustrated with this amp. Now the channels will not even switch!

How did you check the diode?

Whatever was wrong with your amp, now the low voltage supplies also need to be checked.

Double check everything that you have changed and make sure that you correctly replaced the diode and the output transformer.

On the output side of the two large power resistors you should have + and - 15 volts dc. Do you have these voltages?

[guitkrazy]

Welcome.


How did you check the diode?

Whatever was wrong with your amp, now the low voltage supplies also need to be checked.

Double check everything that you have changed and make sure that you correctly replaced the diode and the output transformer.

On the output side of the two large power resistors you should have + and - 15 volts dc. Do you have these voltages?

I actually put the other output transformer back in after seeing that it wasnt bad. The 2 power resistors are they the black and silver ones that are round or the ceramic rectangular ones? Those were so hot. Obviously something is happening for them to emit such heat. But they test good- I was told I have to unsolder the power resistors before testing them? This thing is driving me crazy! The board is black in that area from the emmense heat. Any suggestions you have are greatly appreciated. after replacing that diode I now do not have channel switching.

[52 Bill]

Any suggestions you have are greatly appreciated. after replacing that diode I now do not have channel switching.

The resistors are the two rectangular ceramic ones.

I'll ask again, how did you test the diode?
Do you have the + and - 15vdc supply voltages?

[guitkrazy]

52 Bill thanks so much for your assistance- it has been a struggle- My friend and I have been struggling trying to figure this out. He tested the diodes (I may be wrong as I didn't watch him) but he tested the voltage on both sides when it was only supposed to be showing on one side? If you could see the burning on the back part of the board. We just can't seem to narrow down the culprit. Any help is greatly appreciated! Thank you again!

[52 Bill]

He tested the diodes (I may be wrong as I didn't watch him) but he tested the voltage on both sides when it was only supposed to be showing on one side?

Yes, there will only be voltage on one side of the diodes, but there should be voltages on both sides of the ceramic resistors. There will be somewhere around 50 volts on one side and 15 volts on the other side.

If you could see the burning on the back part of the board.

Yes, I've seen it before. We've discussed it here many times.

The low voltages that I keep asking about run the channel switching circuit. Whatever you guys did when you replaced the diode has messed this up.

Perhaps your friend would like to sign up here and ask/answer more direct questions.

[LBrewski]

FWIW I fixed my HRD when it had developed a similar symptom - but only on the clean channel. It turned out to be cold solder joints on a disc capacitor (carrying signal). I could actually wiggle the cap, it was that loose. After re soldering it's now fine. I did not find any other solder issues on the board but touched it up here and there. Hard to believe I've had this amp for years before the problem surfaced.

My amp also has the toasted pcb underneath the power resistors, does not seem to be an issue though.

[Gtr_tech]

These also suffer from failed plate load resistors in the PI section. Not saying this is your problem, but its becoming common.

[guitkrazy]

Yes, there will only be voltage on one side of the diodes, but there should be voltages on both sides of the ceramic resistors. There will be somewhere around 50 volts on one side and 15 volts on the other side.

Yes, I've seen it before. We've discussed it here many times.

The low voltages that I keep asking about run the channel switching circuit. Whatever you guys did when you replaced the diode has messed this up.

Perhaps your friend would like to sign up here and ask/answer more direct questions.

Bill we checked the voltages on the resistors and we are not getting 15v. they are super hot. do you have anything else we could check out- we are really in a pinch.

[darrellcheng]

Those resistors are supposed to be hot, don't focus too much on them. rather, trace up the circuit, do you have a schematic in hand? a quick google search will land you the schem, as well as a bunch of sites with common issues like yours. also a quick forum search for hot rod deluxe will yield similar results and reading for days on end. anyway, those resistors usually unsolder themselves in those amps . check for continuity between connections in the blacked out part where the damage is. more than likely a trace in the pcb has been ruined, also clean that black stuff with light rubbing while you're at it, it could be causing a short.

good luck, those amps are annoying to troubleshoot

[Enzo]

And the whole Hot Rod series is famous for solder cracking on the power tube sockets.

[52 Bill]

If there is no positive 15v, is there negative 15v on the other supply?

Tell me what you guys did when you changed the bad diode. What was the part number you used to replace it with?

It is possible that you have a shorted chip somewhere in the amp. If the switching circuits were working before you did something to the amp, and now they are not working, you must investigate the work that you did as the cause of the new problem.

[guitkrazy]

If there is no positive 15v, is there negative 15v on the other supply?

Tell me what you guys did when you changed the bad diode. What was the part number you used to replace it with?

It is possible that you have a shorted chip somewhere in the amp. If the switching circuits were working before you did something to the amp, and now they are not working, you must investigate the work that you did as the cause of the new problem.

We actually retested the diode we replaced and it is testing good. We had the same value diode when we replaced it. We actually took the removed diode out and put it back in. I believe the problem lies withing the 2 caps by the resistors. we do not have them and are going to have to get them from somewhere. but regardless, something is pulling the voltage down (which is why we do not have the normal volume output. We have checked every componant in the burnt area and the seem to test fine. Any advice you can give us and have given us is greatly appreciated- Thanks Bill!

[didi]

HI There.
The heat from those two resistors are normal! Start by getting a schematic.
Check all the power supply feed points(marked on schematic by letters A,B,C etc)
If this checks out, use a multimeter set to dc volts. Ground the black(neg) lead. probe the plates of each tube(STARTING FROM THE OUTPUT SIDE OF AMP). You should hear a pop on your speaker as the probe touches the plates. MAKE SURE YOUR VOLUMES ARE TURNED UP. If you reach a plate that pops much softer than the previous one, then you will atleast know in what area the problem lies.
This is just one way of doing it.
OH YEAH< check for dry solder joints, and dirty tube sockets,
Goodluck!!!

[52 Bill]

If the filter cap is shorted or leaky for that matter, the low voltage supply will be pulled down as you noted. Check C40 and C41: 1000mF at 35v.

Next would be to check ic chips U1, U2 and U3.

I'll ask this one, what are the voltages on each side of the two large ceramic resistors R78 and R79 as read to ground?