Vox NT15 various problems

[rockman627]

I only removed the glue on the circuit past r13. Before I give up on this, I'm going to remove all glue everywhere. It doesn't make sense to me since if I lift r13 , voltages before r13 become correct. But sometimes I get lucky.

[g1]

That's the spirit.
There is not a lot of stuff before R13. Even if you are not successful with the glue, I think you could lift components off the board and perhaps solve the problem that way rather than gutting the whole thing an starting from scratch.

[x-pro]

This glue is easily removed if heated with a little hot air from a soldering station thermofan.

[rockman627]

Well it's too late for a thermofan, I already scraped the glue off. Some copper in the traces got exposed, I peeled some skin off the electrolytics and r19, which was entirely gooped and invisible, plus the gain control broke off when I removed the pcb for the tenth time. But I like the idea of removing everything. I'm not going to apply power, but my current goal is to see OL between r13 and ground. Does that make sense? Since there is obviously no rush, I'm going to remove one component at a time and measure, so you may not see an update for awhile, but I will conclude this one way or another.
I meant to say lift, not remove.

[rockman627]

I lifted the ground side of r23. Now between r13 and ground I get 17kohms. Am I getting warmer?

[g1]

I lifted the ground side of r23. Now between r13 and ground I get 17kohms. Am I getting warmer?

Yes, that is significant. R23 is the cathode resistor for V3A and should have no effect on the resistance from R13 to ground.
Was this with the V3 tube in, or out?
I forget if you had removed the V3 socket for inspection under it? What does resistance measure from V3 socket pin 6 to pin 8 ?

[rockman627]

Tubes are currently removed. I did remove v3 and v4 sockets. At that point there was no difference.

With or without tube I read OL.

[g1]

From junction of R13/C14 measure resistance to V3 pin 6, then from same junction to pin 8.

[rockman627]

I get OL at pin 6, and 12.5k ohms at pin 8.

[g1]

Ok, so some issue from tube plate supply to socket cathode pin.
Can you lift one end of R25, then recheck resistance from R13/C14 junction to V3 socket pin 8.
Also from same junction to socket pin 7.

[rockman627]

58k at pin7; 15.3k ohms at pin 8.
BTW, amp is in bright mode.
To be clear, I removed the tube sockets, didn't measure any difference, and put them back in.
Also, we are up to 21k ohms between r13 and ground. To infinity and beyond.

[g1]

58k at pin7; 15.3k ohms at pin 8.
BTW, amp is in bright mode.

Any change for those readings if you change the bright switch setting?