The Old Fender Hotrod Channel Switching issue... or is it?

[lowell]

Hey folks,

Hope everyone is doin' well and staying healthy. I've got a HR Deluxe in where the Channel Select works, but the More Drive does not.

The More Drive LED goes dark upon activating the More Drive switch. There is also no sound when this is engaged. I've searched through the forums for a thread to address this but haven't found one with a similar issue.

I've gone through the TPs and everything looks good to me... or at least close enough as most (not all) of the TPs are a matter of + or - 16v. Here's where I've narrowed it down to.

WITH MORE DRIVE ENGAGED:
TP33 -16v (I believe all that really matters here is that it's close to either + or - 16v in either channel so it's not exact spec, but seems fine to me)
TP36 +17v (lookin' good)

Q3 (This all looks fine)
Vbe -500mv
Vc -16v
Ve +16v
Vce -32v

Q3 tests fine passively with my meter semi function.

All seems good to me! The Red LED measures about 1.5v on the semi test meter function.

I'm a bit stumped... I even shorted Q3 C-E and all that did was light the Green LED -

Here's the schematic, thanks!!
https://www.thetubestore.com/lib/the...-Schematic.pdf

[lowell]

Alright, being the stubborn one, I couldn't quit even after posting this... and went back through things with my meter. Instead of measuring at Q3 Collector this time, I measured at LD1 Red Anode - That small change in approach (toughing the LED lead with my meter) revealed the issue. The LED is has a cold solder joint and is working fine if I mess with it. So.... hope this helps someone else with the same issue!

Very strange that Q3 Collector had -16v on it though when it wasn't working. And very odd that measuring semi test function from R84 to Q3 C did not reveal any issue... my meter still showed the LED as being there.

[nevetslab]

Hey folks,

Hope everyone is doin' well and staying healthy. I've got a HR Deluxe in where the Channel Select works, but the More Drive does not.

The More Drive LED goes dark upon activating the More Drive switch. There is also no sound when this is engaged. I've searched through the forums for a thread to address this but haven't found one with a similar issue.

I've gone through the TPs and everything looks good to me... or at least close enough as most (not all) of the TPs are a matter of + or - 16v. Here's where I've narrowed it down to.

WITH MORE DRIVE ENGAGED:
TP33 -16v (I believe all that really matters here is that it's close to either + or - 16v in either channel so it's not exact spec, but seems fine to me)
TP36 +17v (lookin' good)

Q3 (This all looks fine)
Vbe -500mv
Vc -16v
Ve +16v
Vce -32v

Q3 tests fine passively with my meter semi function.

All seems good to me! The Red LED measures about 1.5v on the semi test meter function.

I'm a bit stumped... I even shorted Q3 C-E and all that did was light the Green LED -

Here's the schematic, thanks!!
https://www.thetubestore.com/lib/the...-Schematic.pdf

What are you reading at TP35 with More Drive Switch OUT (YEL) and Switch IN (RED)? The only way I can see losing signal in the More Drive mode is for Relay K2 not engaging anymore. TP35 changes from -0.54V to -10V with More Drive Switch OUT vs IN (using control panel switch). I've also had issues with the NJR4560 Op Amp when More Drive isn't working. The two FET's Q1 and Q2 are involved in changing the gain of the Drive/More Drive circuit, but NOT involved in signal routing. Relay K2 is somehow turning off, while Relay K1 remains engaged.