Laney TT50H No Outout

[ca7922303]

Have you had V5 tube socket removed yet? One of the pictures shows a bit of discoloration from the underside.
With such an odd problem it would be worth removing it and inspecting it and the board where it mounts.

Yeah, I was noticing alot of soot under V-5 last night. I'll remove socket and forward photos asap. Thanks.

[g1]

Have you had V5 tube socket removed yet? One of the pictures shows a bit of discoloration from the underside.
With such an odd problem it would be worth removing it and inspecting it and the board where it mounts.

[ca7922303]

Maybe you are counting pins from the wrong side. Pin9 of preamp tubes should go to one side of hum pot, pins 4 & 5 should go to the other side of the pot.

It is best to not use the term 'continuity' with electronics. Specify the actual resistance value instead. Or say 'short' if it is around 0 ohms, maybe up to 2 ohms.
Continuity works ok in 'go/no go' wiring applications like automotive, but most meters will indicate continuity for anything between 0 and 40 ohms, or some meters as high as 200 ohms. In electronics, the difference between 0 and 40 ohms can be critical.

Checked pins connecting him balance to preamp tubes V1-V6. Getting 0.00 ohms on all.

[g1]

Just noticing that one pin of hum balance pot has continuity with pin 1 of V1-V6 and the other hum balance pin has continuity with pin 5 of V1-V6. Searching around board to see if either hum balance pins have continuity with anything else and so far not finding anything. The third pin of hum balance has continuity with R52.

Maybe you are counting pins from the wrong side. Pin9 of preamp tubes should go to one side of hum pot, pins 4 & 5 should go to the other side of the pot.

It is best to not use the term 'continuity' with electronics. Specify the actual resistance value instead. Or say 'short' if it is around 0 ohms, maybe up to 2 ohms.
Continuity works ok in 'go/no go' wiring applications like automotive, but most meters will indicate continuity for anything between 0 and 40 ohms, or some meters as high as 200 ohms. In electronics, the difference between 0 and 40 ohms can be critical.

[ca7922303]

Any time you have a burn leaving carbon in a high voltage circuit you must remove all the carbon, or you will have a path for the high voltage. That may be what is happening here as the cap has the high voltage and the hum balance pot is near ground potential.
Any carbon should be thoroughly scraped away, or even better, cut out. You may have to cut or drill away a piece of the board, then rebuild the traces with wire.

Removed R43 and will be removing epoxy from board shortly. Just noticing that one pin of hum balance pot has continuity with pin 1 of V1-V6 and the other hum balance pin has continuity with pin 5 of V1-V6. Searching around board to see if either hum balance pins have continuity with anything else and so far not finding anything. The third pin of hum balance has continuity with R52.

[g1]

Any time you have a burn leaving carbon in a high voltage circuit you must remove all the carbon, or you will have a path for the high voltage. That may be what is happening here as the cap has the high voltage and the hum balance pot is near ground potential.
Any carbon should be thoroughly scraped away, or even better, cut out. You may have to cut or drill away a piece of the board, then rebuild the traces with wire.

[ca7922303]

Nothing suspicious looking there. And there are only traces on one side for that cap. Follow those traces to see if there are any accidental solder bridges anywhere.
I don't see any reason why that C37 cap being in place would cause the DC on the hum balance pot (if it's not there without the cap).
You might want to verify again that the DC on the hum pot is gone with cap out and returns with cap in.

Installed board and C37 again. With no power/preamp tubes installed, amp mains on or on standby, Variac to 100v, hum balance pot is reading 100vdc, same reading as R43 and one(1) end of C37. Other end of C37 is 0.

[ca7922303]

Nothing suspicious looking there. And there are only traces on one side for that cap. Follow those traces to see if there are any accidental solder bridges anywhere.
I don't see any reason why that C37 cap being in place would cause the DC on the hum balance pot (if it's not there without the cap).
You might want to verify again that the DC on the hum pot is gone with cap out and returns with cap in.

The big power resistor near C37 burnt a hole in board awhile back. I used epoxy to repair the hole and replaced that resistor. Could it be that board is damaged to the point of causing the bias pot issue?

[g1]

What do you make of the board photos?

Nothing suspicious looking there. And there are only traces on one side for that cap. Follow those traces to see if there are any accidental solder bridges anywhere.
I don't see any reason why that C37 cap being in place would cause the DC on the hum balance pot (if it's not there without the cap).
You might want to verify again that the DC on the hum pot is gone with cap out and returns with cap in.

[ca7922303]

This makes no sense to me. Even if the new C37 was faulty and shorted, it should have no connection to the heater circuit whatsoever. And if there is some kind of board fault, it should be there whether the cap is installed or not.

Can you post pics of where the cap goes, with cap removed? Both sides of circuit board.

What do you make of the board photos?

[ca7922303]

This makes no sense to me. Even if the new C37 was faulty and shorted, it should have no connection to the heater circuit whatsoever. And if there is some kind of board fault, it should be there whether the cap is installed or not.

Can you post pics of where the cap goes, with cap removed? Both sides of circuit board.

Photos of both sides of board. Traces are not in great shape, but I do have continuity down line in both directions when C37 is soldered in place.

[g1]

This makes no sense to me. Even if the new C37 was faulty and shorted, it should have no connection to the heater circuit whatsoever. And if there is some kind of board fault, it should be there whether the cap is installed or not.

Can you post pics of where the cap goes, with cap removed? Both sides of circuit board.

[ca7922303]

So with C37 installed, there is over 300VDC on the hum balance pot, but with C37 removed, that DC is not there?

That is correct. No red glow, no smoke, and no voltage on either component. R52 still reads 100 ohms, and hum balance pot did not melt like original one did.

[g1]

So with C37 installed, there is over 300VDC on the hum balance pot, but with C37 removed, that DC is not there?

[ca7922303]

It seemed there was no problem with anything involved with the heaters until you replaced C37. That is when R52 and the hum balance pot started to burn.
Triple check your work looking for any solder bridges, bent tube socket pins, etc. Also check both sides of all tube sockets for any signs of arcing (carbon).
You might even want to remove C37 and check underneath it. I had a Vox AC15 in where they ran a heater trace under the filter cap. The trace arced to the cap lead, but you couldn't see it til the cap was removed.

This is a double sided circuit board, so there are a lot more hidden areas.

Removed C37 and was able to take variac to 104v(400vdc on board) without any voltage reading on hum balance pot or R52. Didn't find anything under C37. Put some solder on two(2) spots showing copper on the board near V5. Nothing else obvious that I see.