JCM 2000 DSL no output

[sweatyk]

The tubes did not flicker.....it was the power switch. I'm going to take a step back and check all of the tube sockets where I flowed new solder. I may have created an issue that is unseen. Possibly take the time and remove them all check them out and reinstall them if they are ok. It seems that something I've done has changed things so I will start there. I'll check back after I complete this task.

[sweatyk]

I removed all of the tube sockets from the PCB tonight to inspect for any problems under them. All of the sockets looked to be good but V8 had a strange discoloration in one spot. It wasn't burnt but looked more like someone sprinkled some silver dust on it as if something nearby might have went belly up and some point in it's life. It's very slight but should it be a concern? I hope that it shows up in the pics. Let me know if this could be an issue.

[52 Bill]

It wasn't burnt but looked more like someone sprinkled some silver dust on it as if something nearby might have went belly up and some point in it's life.

Do you use a solder sucker to desolder joints? That looks like the solder dust that they will sometimes create. Clean it off with a alcohol swab.

[sweatyk]

Upon further inspection I found this dark spot inside of the V7 socket along pin 2. I looked inside the pin hole and it does appear to have a slight discoloration on the other side. It's too small to see but it sure does appear cracked and creating an arc. Not sure if this is what's entirely wrong with this amp but this sure doesn't look like it's helping anything.

[Leo_Gnardo]

Upon further inspection I found this dark spot inside of the V7 socket along pin 2. I looked inside the pin hole and it does appear to have a slight discoloration on the other side. It's too small to see but it sure does appear cracked and creating an arc. Not sure if this is what's entirely wrong with this amp but this sure doesn't look like it's helping anything.

The silvery debris you mentioned earlier may be carbon. As the plastic breaks down during an episode of arcing it turns into conductive carbon & you'll do well to replace that socket without another thought.

[sweatyk]

The silvery debris you mentioned earlier may be carbon. As the plastic breaks down during an episode of arcing it turns into conductive carbon & you'll do well to replace that socket without another thought.

I'm going to suggest to the customer to replace all of the sockets while I have them out. I'm hoping this resolves it but my luck is there is a secondary issue to deal with. I hope not. BTW......love that avatar. I remember watching that as a kid.

[Mark Black]

I'm going to guess there is (was) through-hole plating in the V7 Pin-2 hole which has arced and is now gone after carrying current to the rest of the preamp tube heaters, so be sure to solder the top and bottom pads for at least that pin if not all.

[Jazz P Bass]

That could also explain the spatter.

[Zouto]

Did you check BR1, BR62 bridge rectifier for DC filament supply (V1 & V2)? These rectifiers tend to get overheated, quit their services & keep some tubes too cool. Better swap 'em and keep the leads a bit longer for some ventilating distance to the pcb.
Good luck,
Zouto

[sweatyk]

Sorry for the delay. Had to take a small sabbatical for health reasons. Plus I was waiting for the new tube sockets to arrive. So here's where I'm at with it. Replace all sockets. Also on one side of C46 there was a previous replacement and the traces had evidently burnt and lifted a bit. Who ever repaired it didn't do it to last. I found that connection to be intermittent so I performed a more solid connection. Hooked it to my current limiter without any tubes in it. No shorts or issues. Put the tubes in it and they all lit up. However with the tubes in the lighted "power" switch will not light up. It will when the tubes are out. I proceeded and plug an input cord in to see if i could get sound.....no sound on either channel. I'm done for the night but wanted to see if you guys had any thoughts on the power switch only lighting up with no tubes installed.

[g1]

Was it on the current limiter when the power switch would not light?
It sounds like you are just on the threshold of whatever voltage triggers the light. When you pull tubes, the voltage comes up enough to turn on the light.
It can also happen if the line voltage coming out of the wall is a bit low.

[sweatyk]

WHY???????......here's what i did. Plugged the amp directly into the wall outlet. Power switch turned on and ALL of the tubes begin to glow........great so far. Then I plug a guitar in and flip on the standby switch. Next thing you know I'm hearing my guitar (and I'm doing the happy dance). I turn it off....pulled the power cord and went to bed. That was last night.....fast forward to just a few minutes ago. All I did was plug in the power cord and turned the power switch on. This is where my happy face quickly changes. The only tubes that lit up were V6, 7, 8....and no output. The very same problem I started this thread with........WTH?

[sweatyk]

Can anyone explain how that can happen? To recap.....only parts that have been replaced are the tube sockets. Plus I reinforced one side of C46 as it was intermittent. So 24 hours ago everything lit up and played. Without moving this amp from where it was since it worked it has now returned to the original symptoms it was brought to me with. I'm having a hard time wrapping my mind around it.

[g1]

You had an intermittent problem that is still intermittent. It's not that uncommon. Sometimes it seems like you have fixed an intermittent but the problem comes back.
Can be very frustrating for the customer. Fortunately it is failing again for you, rather than for the customer in the middle of a gig.

[DrGonz78]

That is the problem with some intermittent failure, and why they are the hardest to repair. At this point you need to look at the amp as if this thing is on the bench for the first time. Do all the things you would do to inspect all the traces and interconnections, even if it feels like the same familiar road. Carefully inspecting the amp will be the place to start again. Somewhere there is an intermittent or so I think. Take a deep breath and even put it aside for a bit. Best of luck too.

Edit: Simulpost>>> G1 beat me too it. Sounds like he's nothing but an old resentful amp 'repairman'...