JCM2000 DSL Silver Edition problems.

[gtrplayr1976]

Anyone have any repair experience with these ? It looks new. Friend brought it to me. Said when he took it out of standby he heard a pop ,and a smell ,and no sound ,but the tubes light up.
I opened it ,and found some obviously smoky parts. I also understand there are issues with the main boards on these. I thought I would try to just replace the obvious ,and give it a try before replacing the board. I have it up to voltage , but showing little to no bias current. I have my DMM connected to the bias plugs ,and my Weber bias probe on each set of tubes. 515 volts ,but no current? Adjusting the pots did nothing. What am I missing ?
Thanks folks!

[g1]

Are those resistors you replaced holding up? They kind of all lead to C31 which may be suspect.
How is the screen voltage on the power tubes (pin4)? Also check R6 and R9 cathode resistors for the power tubes.

[gtrplayr1976]

Are those resistors you replaced holding up? They kind of all lead to C31 which may be suspect.
How is the screen voltage on the power tubes (pin4)? Also check R6 and R9 cathode resistors for the power tubes.

The resistors seem fine right now. I replaced them with ceramics. I'll check those voltages ,and resistors.

[gtrplayr1976]

Are those resistors you replaced holding up? They kind of all lead to C31 which may be suspect.
How is the screen voltage on the power tubes (pin4)? Also check R6 and R9 cathode resistors for the power tubes.

Hard to read the resistance with it in circuit , but I was getting .6/.7 ohms ,and the voltage on all pin 4s at -.642

[gtrplayr1976]

Are those resistors you replaced holding up? They kind of all lead to C31 which may be suspect.
How is the screen voltage on the power tubes (pin4)? Also check R6 and R9 cathode resistors for the power tubes.

g1, I was checking bias voltage without tubes. I have 22VAC ,and -29VDC at the anodes of D7,and D8. Nothing on the cathode side. I have -58.6VDC at the anodes of D9 ,and D10 ,and 22VAC on the cathodes. These are at the bias supply at the xfmr. D7 ,and D8 seem to be bad ?

[g1]

What is the DC voltage on either side or R71? (you can measure at D3 cathode and R72)
Those diodes should be ok, -58VDC is good for the bias supply.

[gtrplayr1976]

What is the DC voltage on either side or R71? (you can measure at D3 cathode and R72)
Those diodes should be ok, -58VDC is good for the bias supply.

Ha...519VDC at the cathode of D3 ,nothing at R72.

[gtrplayr1976]

So this would mean another dropping resistor in that line failed. I just missed it because it didn't look burned up like the other three. I should have checked the plate voltages ,and I would have known. I guess my question now would be ,WHY did all these dropping resistors fail ?

[Intripped]

WHY did all these dropping resistors fail ?

I think that it's because C31 and/or C14 got shorted to ground: this caused in all the dropping resistors a great current, way too much for their power rating

[gtrplayr1976]

I think that it's because C31 and/or C14 got shorted to ground: this caused in all the dropping resistors a great current, way too much for their power rating

C14 DID blow up ,so it could be. I'll check C31 when I take the board out again. Not sure how they would have shorted to ground though ?

[g1]

C31 and C14 each have 1 leg connected to ground. If either/both short, all those resistors you replaced burn up.

[gtrplayr1976]

C31 and C14 each have 1 leg connected to ground. If either/both short, all those resistors you replaced burn up.

So far the replaced ones have held up. I still have to replace the 7 watt , 270R ,but it's further down the line. I'll have to order some.

[g1]

The 7watt is first in the chain, so none of the others are getting any voltage until that one is replaced. At the very least do a resistance check across C31 before you fire it up.

[gtrplayr1976]

The 7watt is first in the chain, so none of the others are getting any voltage until that one is replaced. At the very least do a resistance check across C31 before you fire it up.

Correct. I'll take a close look at it when I pull the board back out. C14 has been replaced already since it basically blew apart. I might have another cap, so I may just replace it to be on the safe side.

[g1]

If C14 blew apart then it was the likely cause of the problem.