Anyone work on a Fender red knob Super 60?

[Prairie Dawg]

I've got one here that a guy found in a pawnshop and brought to me to revive. Overall it was in pretty fair shape and powered up OK, and after replacing the two broken jacks I thought I was in like Flynn. I found out that using the push button switch on the front of the amp the drive channel works fine but the normal channel has only one setting and that is full volume no matter what you do. I've heard these amps have some sort of ultra weird science optocoupler resistors that could be an issue but I'm just starting to dive into this one. At this point I don't have a clue.

It's not the easiest amp to work on because to access anything you have to remove the circuit board.

Ideas? Thoughts?

Thanks

[Enzo]

Amps are amps, we work on them all.

Also could just be a bad volume control.

The controls are on the narrow front board, so if you need to get at that, I just double up a towel or a section of newspaper, lay it on the main board, dismount the controls board and flip it back onto the towel. Now the parts are facing up at me.


Nothing cosmic about this, the volume control has its "ground" end connected through an optocoupler. Turn the opto on and the control is grounded like any volume control, so it works. Turn off the opto, and the circuit opens and the volume control is left floating, so it has no effect - ie you can't turn it down. But an open pot acts that way too, or a pot with broken solder.


The optos are wired in serieis, though they are dual types. SO does your other channel switching work? DO the gain channel controls work and then go dead as you switch between channels - like they should? If so, the optos are working, unless 1/2 of one died.

[Prairie Dawg]

Those are great suggestions and I thank you. I learn far more from my struggles than the few easy victories I get.

I had the control board out to change the two broken jacks but at that point I hadn't powered it up to see what the amp was or was not going to do. It oughtta be an easy enough thing to check the vol control at that point and eliminate or rule it in the next time I pull the board out which is going to be tomorrow morning. Right now it's beer past thirty.

[Gtr_tech]

I've had a couple of the super 60s thru here. Bad optocouplers in both.

[Enzo]

check the volume control wher it sits with your o0hm meter. Open is open.

[pdf64]

The optocouplers in a Super 60 I worked on last year had previously been replaced.
It's worth fitting the optional bias adjustment trimmer.
Pete

[Prairie Dawg]

It turned out that OP1 was on the fritz. All is well and it went home today.

Thanks everyone who contributed knowledge and wisdom to this project.