HRD Channel Switching issue

[Mr_bibbles]

Hey All,

HRD on the bench, won't switch out of normal channel. Been searching forums for an answer, but can't seem to find one for this specific problem. Tried shorting footswitch jack, no avail. No change in voltage on J111's when using the panel switch. LED not lit (normal for clean operation.)

https://www.thetubestore.com/lib/the...-Schematic.pdf

Checked and double checked solder joints around power supply, had hit up the 5 watt resistors and zeners already. Voltages are off by about a volt:

5w Resistors R78 and R79 measure:

17.15 ----> 47 vdc
-17.35 ---> -47 vdc

Given voltages on schematic are 48/16 (-/+ respectively.)

SO we have an issue of the 16v zener diodes not holding the voltage at 16-/+, but in my ignorance, I don't know how to go about correcting this. Shotgun replacing the Zeners might work, but i don't really understand the WHY here. Could there be leakage from the caps around that stage? Do I need to triple check the traces around there? If something was pulling current after the stage, it would be "lower" than 16, not higher, right? That leaves a very limited area to check, as the IC's wont operate in this range anyways??

Thanks a lot,

Mr. B

[Mr_bibbles]

It turned out to be R97! Barely visible trace lifted up on one side blocking the 39AC from passing. Voltages dropped back down to 16.3 / -16.5 so this answers all my questions.

[nevetslab]

It turned out to be R97! Barely visible trace lifted up on one side blocking the 39AC from passing. Voltages dropped back down to 16.3 / -16.5 so this answers all my questions.

Don't ya love it when you find that one pesky little fault hiding in plain sight on Fender's PCB's? Their PCB quality level, with regards to pad size and copper adhesion from the raw PCB material end of things is not so good....traces and pads lift WAY TOO Easily! Good find!