Fender 68 Custom Vibrolux Reverb Tremolo/bias Problem

[Helmholtz]

Measure leakage resistance of C50 and C24.

[tubeswell]

Pull the 6V6s out and check both Pin 5s for bias voltage. If there's no bias voltage at pin 5, but there is a negative bias supply voltage on the bias supply filter cap, then use your R-meter to check for DC-continuity between the bias supply and Pin 5. Could be a bad trace or jumper somewhere. This is a new amp so should be returned under warranty.

[jasonguitar]

If brand new and failed so soon, I would return it to the supplier for replacement or at least order free of charge parts from Fender as a warranty repair which will mean I would get paid for repairing their new faulty amplifier.
If I were the purchaser, I would expect a replacement and not accept a repair as is my consumer right.

Neither C24 or C50 are leaking.

The owner said they were unable to get Fender to replace it because of limited inventory and his local authorized service centers either have a bad rep or are booked up for weeks so he was hoping I could help get it sorted.

[Chuck H]

If it matters... After reading through this I'm thinking bad intensity pot as Pete implicated.

[jasonguitar]

If it matters... After reading through this I'm thinking bad intensity pot as Pete implicated.

I stated previously that the intensity pot, and the speed pot for as well for that matter, are functioning properly. I pulled them out and checked them.

[pdf64]

But the bias voltage is controlled smoothly by adjustment of the intensity pot. The pot is working “properly.”

So the bias is at its normal full voltage at the CCW setting, and 0V or what, at the CW setting?

I’m reminded of occasional reports I’ve read, of Fender pots having a short between track and case.

[The Dude]

I had a Fender come in a while back with that very problem. I shot some air into the pot and a chunk of solder came out.

[jasonguitar]

Thanks to everyone for your efforts to help me with this. Apparently it was a cold factory solder joint because after pulling out the related components, testing them, finding no issues and replacing them, the bias is now modulating properly and everything is functioning correctly. Cheers!