Fender HR Deville Had a Drink.

[Pryde]

What voltage do you read across R74?!? That's sort of the point of this test.

If R68 is burning up, especially with a dim current limiter, something is horribly wrong. Do you have the amp plugged into a load? It's a stretch, but with the filter cap disengaged there may be instability in the PI such that it's causing overdissipation.?.

The amp is hooked up to a load.
I didn't get a measurement across R74 because R68 started arcing and burned quickly so I shut it down.

[Chuck H]

The next thing I would try would be a replacement for C35 and R68... And the current limiter. That's all I have right now.

[Pryde]

The next thing I would try would be a replacement for C35 and R68... And the current limiter. That's all I have right now.

Thank you. I replaced R68 and left C35 lifted. Powered amp up with bulb limiter and no parts are burning (that I can see/smell). BUT there is a lot of static, popping, noise etc. coming through the test speaker/load. I measured voltage across R74 at 98vDC. This is with C35 lifted. Thoughts?

[g1]

Schematic shows about 40V across R74, you are double that.
What is the voltage across R75?
If you remove V3, what is the voltage across R74?

[Enzo]

The following is only for science and education, I do not think the PI is burning up your resistors.

The PI thing, the PI B+ node is 440v. Pick the 100k resistor. let us assume the plate, pin 6, is a dead short to ground. That would leave 440v across the 100k resistor, and Ohm's Law tells us that 4.4ma flows. That would mean the 100k has to dissipate close to 2 watts, so it would likely burn up, but that 4ma would not be remotely enough to burn up R74. A similar calculation shows the 82k also innocent.


Now back to your issue.

I see no way the circuit can burn up R68. Where is R68 physically, I don't spot it? Oh wait, right by the control. OK, here is my latest idea. Your findings just don't make sense in terms of the circuit. Flip the board over and follow the trace from the non-ground end of R68 over across the board to where it crosses through the ribbon to the tube board. Look especially close where it passes the traces from the hot end of C35. We are looking for a tiny spot where they are close that they can arc.

Here is an old trick. next time you feel like spending a new resistor, turn off ALL the room lights before turning on the standby switch. Look closely at the board. If you see any tiny blue spark, even the smallest little blue point of light, that is an arc.

[Chuck H]

I see no way the circuit can burn up R68. Where is R68 physically, I don't spot it? Oh wait, right by the control. OK, here is my latest idea. Your findings just don't make sense in terms of the circuit. Flip the board over and follow the trace from the non-ground end of R68 over across the board to where it crosses through the ribbon to the tube board.

AAaaahhh... I totally forgot about the ribbon cable connections! I don't do repairs so I just see amps in my head made of non computer parts I just couldn't figure how even a beer spill could make R68 toasty. Arching (and possibly a carbon trace now) at the close proximity ribbon connection. I was a little surprised in post #3 when pryde asked if it should be cleaned. I would have assumed that would be the first thing to do. And that should include a toothbrush on those ribbon pins. You know, the place where the beer pooled and it's all sticky! Yeah. Clean that.

[Pryde]

Schematic shows about 40V across R74, you are double that.
What is the voltage across R75?
If you remove V3, what is the voltage across R74?

Voltage across R75 is ~10vDC
With V3 out voltage across R74 is ~110vDC

Per Enzo's trick I fired it up in the dark and an arc occurred ONCE very briefly and I could not tell where it came from exactly as I just seen a quick flash lite up with back chassis wall. I powered down and back up again and can't see any more arcing but the crackle/pop is still present as ever.

It is possible it came from the tube board underneath but close inspection with a mirror doesn't show any arced areas. Will keep hunting and hopefully I will be able to spot something.

[Pryde]

Well I thoroughly cleaned tube board, checked for arcs and did not see anything. cleaned all tube sockets as well. The amp actually fired up and was working for about 2 minutes and stable with bulb limiter. Shut it down and tried full power and R68 gave up the ghost again burning up quickly.

Not sure what else I can do at this point. Might have to call it quits ???

[52 Bill]

Have you actually tried replacing V3? How many volts are across R68?

[Pryde]

Have you actually tried replacing V3? How many volts are across R68?

Yes tried replacing V3 and no change. I will need to dissasemble everything and replace R68 again to get a voltage measurement there. She goes up in smoke very quick though.

[bsco]

Well I thoroughly cleaned tube board, checked for arcs and did not see anything. cleaned all tube sockets as well. The amp actually fired up and was working for about 2 minutes and stable with bulb limiter. Shut it down and tried full power and R68 gave up the ghost again burning up quickly.

Not sure what else I can do at this point. Might have to call it quits ???

Sometimes I feel the same way......hang in there...the guys here are experts....they will help you figure it out....

[52 Bill]

Yes tried replacing V3 and no change. I will need to dissasemble everything and replace R68 again to get a voltage measurement there. She goes up in smoke very quick though.

There can only be a few normal ways for any voltage to get to R68. Remove V3 and measure the voltage across R68. Hopefully without the tube there will be no voltage there. If there is voltage there then the tube socket or the pc board may be carbonized or there may be a problem with the output transformer.

[TimmyP1955]

Measure the voltage on V3, pins 3 and 8 (the cathodes) - it should be 43V. If it is higher, pull V3.

Now what is it? If there's any voltage at all, check the voltages on the far (from V3) side of C24 and C25 - those should be less than 1V on C24, and 0 (theoretically) on C25. If there's voltage on C25 (and therefore on R68), remove the gray NFB wire from the OPT. If the voltage goes away, you have a primary to secondary short in the OPT. If no change, C24 or C25 may be leaky or shorted.

Oh: The schematic says 14.7V on the plates of V3 - should that not be more like 147?

[bsco]

Pryde......I am curious......what area or areas of the amplifier had the drink spilled into it??

[Pryde]

There can only be a few normal ways for any voltage to get to R68. Remove V3 and measure the voltage across R68. Hopefully without the tube there will be no voltage there. If there is voltage there then the tube socket or the pc board may be carbonized or there may be a problem with the output transformer.

I tried this and there is 97vDC across R68 with V3 removed.