Can this be fixed? Biasing blunder

[ledvedder]

I need to know if this can be fixed, or if it's something covered under warranty. I was biasing my JCA2112RC and the lead of my multimeter slipped in my hand. Then, the spot near the bias point started flashing and burning and making a crackling sound through the speaker. I quickly turned the amp off and pulled the plug. Now, I have this.

When I turn the amp on, on standby, it has a loud hum. As soon as I turn the standby off, the spot on the board starts flashing and burning again.

Here is what the other bias point (the one that is still good) looks like.

Please help! I hope I didn't really screw this up, since I just got it Friday.

 

[The Hoff]

I'd be happy to help you out but, I don't know the tech side of amps. I know people here do know though so, I hope you get some assistance. Good luck.

(free bump)

 

[steve_k]

Even though it looks burned, the circuit still looks in tack, from the pictures anyway. See if you have continuity across the the burned spot.

 

[ledvedder]

Even though it looks burned, the circuit still looks in tack, from the pictures anyway. See if you have continuity across the the burned spot.

Can you explain how I do that?

I'm thinking that it may have created a solder bridge between the pin of V5 and the brown wire? Should I remove the solder from these areas?

 

[JerryP]

It can be fixed, but it's something you should have a tech do. Don't keep turning it on, you'll just do more damage. It looks like it's shorted from the plate terminal of the tube socket to the heater cirucit trace and possibly to ground at that screw. Once you have a carbon track on the board from something arching you will always have a path for electricity to follow. The burnt area of the board must be cut out and probably a section of that heater trace. Not a big deal as long as it didn't do any other damage when it happened.
Jerry

 

[CaseyCor]

Looks like you created a false path for the electricity to follow. You'll most likely have to have that section of the board cut out.

 

[glpg80]

you wont need to cut it out.

arc flash carbon can be removed with special cu-tips made for PCB board use (not ear wax models) and 91% or greater isopropyl alcohol.

once the carbon is removed, use a wick to remove the solder from each point.

reflow the components and replace the charred wiring. problem fixed.

out of all of the carbon flash repairs i have done i have never had to "cut out" anything on a board. carbon flash is surface contained and most PCB's have a board coating that you could (should) also replace once the repairs are finished.

if cutting out is needed, its not because of the carbon. its because of turning it on/off on/off repeatedly in its current condition that results in distorting and overheating the PCB board.

 

[racerevlon]

It can be fixed, but it's something you should have a tech do. Don't keep turning it on, you'll just do more damage. It looks like it's shorted from the plate terminal of the tube socket to the heater cirucit trace and possibly to ground at that screw. Once you have a carbon track on the board from something arching you will always have a path for electricity to follow. The burnt area of the board must be cut out and probably a section of that heater trace. Not a big deal as long as it didn't do any other damage when it happened.
Jerry

^^^This +1,000,000

 

[Marshall Law]

Looks like you created a false path for the electricity to follow. You'll most likely have to have that section of the board cut out.

Polly want a cracker

 

[JerryP]

you wont need to cut it out.

arc flash carbon can be removed with special cu-tips made for PCB board use (not ear wax models) and 91% or greater isopropyl alcohol.

once the carbon is removed, use a wick to remove the solder from each point.

reflow the components and replace the charred wiring. problem fixed.

out of all of the carbon flash repairs i have done i have never had to "cut out" anything on a board. carbon flash is surface contained and most PCB's have a board coating that you could (should) also replace once the repairs are finished.

if cutting out is needed, its not because of the carbon. its because of turning it on/off on/off repeatedly in its current condition that results in distorting and overheating the PCB board.

When the board is burnt like that there's nothing but carbon left. I don't have it in front of me, but every other amp I've seen that looked like that was burnt right thru. Cutting it out is the only repair. With low voltage you might get by repairing, not with high voltages.
Jerry

 

[ledvedder]

Could I just cut the trace and attach a wire? Something like the attached picture?

 

[JerryP]

Could I just cut the trace and attach a wire? Something like the attached picture?

I would do just like you show in the picture, but I would also drill out the burnt spot or trim it out with a Dremel tool. It looks like that burnt area goes all the way over to the screw which will be a ground path. Use heavy gauge wire (18 or 20 awg) to jump the trace because that circuit carries a high current.
Jerry

 

[Bogged]

Good thing you're still here to tell us about it.

 

[Anonymous]

Ya lost me at..."Will it be covered under Warranty??".....sorry....J/k...Glad ya didn't microwave yourself!@!

 

[ledvedder]

Well, I was able to fix it by cutting the trace and using a jumper wire. I also cleaned up the board and the solder points.

 

[ledvedder]

Well, I thought I had everything fixed. While I had the chassis out to fix it, I unplugged the red and white wires from the reverb tank. I didn't plug them back in until tonight, when I was putting everything back together. I now have no reverb. I tried reseating the tubes, since 2 of them drive the reverb, but I'm getting nothing. And ideas?

 

[Dallas Marlow]

Well, I thought I had everything fixed. While I had the chassis out to fix it, I unplugged the red and white wires from the reverb tank. I didn't plug them back in until tonight, when I was putting everything back together. I now have no reverb. I tried reseating the tubes, since 2 of them drive the reverb, but I'm getting nothing. And ideas?

Silly question but is it possible you plugged them in backwards? red in white etc., ? I have no idea about reverb tank ins and outs, but I can't even think of what else would be wrong with that, consider your amp is playing I don't know why your reverb tank would stop working from tubes, wouldn't the amp be at least kind of lethargic if the tubes weren't working?

 

[Motorpud]

Well, I thought I had everything fixed. While I had the chassis out to fix it, I unplugged the red and white wires from the reverb tank. I didn't plug them back in until tonight, when I was putting everything back together. I now have no reverb. I tried reseating the tubes, since 2 of them drive the reverb, but I'm getting nothing. And ideas?

Silly question but is it possible you plugged them in backwards? red in white etc., ? I have no idea about reverb tank ins and outs, but I can't even think of what else would be wrong with that, consider your amp is playing I don't know why your reverb tank would stop working from tubes, wouldn't the amp be at least kind of lethargic if the tubes weren't working?

That would be my suggestion too Double check to make sure they aren't plugged in backwards. I bought an amp used that had no reverb, it was cool with me and since I wasn't going to use it I never even checked it. After a while one of the switching relays was acting up so I took it to my local tech and to get it fixed. When I went to pick it up he told me he noticed the reverb was plugged in backwards when he was in there

 

[ledvedder]

I checked to make sure the red and white wires are plugged in correctly, and they are.