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View Full Version : Wierd runaway volume issue tonight!

Ascension
08-03-2008, 12:18 AM
My Fender Prosonic combo tonight suddenly went to full volume when I switched the channels to the crunch side with the footswitch tonight:NUTS. I'm talking full volume and the master volume controll was non active. Hit the footswitch and the clean volume was fine hit the switch a second time for the crunch again and it was WIDE OPEN. I unplugged the switch from the rear and then replugged the switch into the rear jack and now it's fine and I can not recreate the problem but WHA???
I am a P/W player and this was at a church in the middle of the service when it wet nuts so it was:eek: and :hide . I have NEVER seen this happen before and I don't have a clue what would cause this issue. Maybe it was some kind of glitch with the channel switching relay?? But why the heck was the volume suddenly running wide open and the pot inactive??? Anybody got some ideas on this??
hamfist
08-03-2008, 02:35 AM
I'm afraid I can't help on that one, but can only empathise on the embarrassment of that happening in church. :o
ClinchFX
08-03-2008, 04:41 AM
Not a definitive answer, but runaway volume can be caused by a faulty ground connection, particularly at the ground end of a gain or volume pot.

Peter.
Ascension
08-04-2008, 11:15 PM
Not a definitive answer, but runaway volume can be caused by a faulty ground connection, particularly at the ground end of a gain or volume pot.

Peter.
Yep I have seen that before but this was different. When I unplugged the footswitch from the rear and re plugged it back in the amp went back to normal. I can't get the problem to recreate it's self so far but :worried!
brad347
08-04-2008, 11:37 PM
It's good that it happened in church. There was an old lady in the back and you scared the hell out of her.

(sorry!)
donnyjaguar
08-05-2008, 09:15 AM
Clearly, the almighty has a sense of humor. :) +1 on the bad ground on the gain pot. Some amplifiers use the body of the control for ground so if the nut, and consequen6tly the knob, is loose this would explain it.
brad347
08-05-2008, 09:19 AM
Clearly, the almighty has a sense of humor. :) +1 on the bad ground on the gain pot. Some amplifiers use the body of the control for ground so if the nut, and consequen6tly the knob, is loose this would explain it.

to that end you could always try rocking the gain knob back and forth to see if you can get the problem to reproduce.
ClinchFX
08-06-2008, 10:15 PM
I haven't worked on any of the more modern Fender tube amps, but I found time to have a quick look at the Prosonic schematic. I noticed that the Master is a dual pot with one section in the crunch channel, and the Gain 2 pot is also a dual pot with one section in the master area. At a quick glance, it appears that a sticky relay could possibly be the cause of your problem, because Relay 2 can bypass one section of the master. If one of the relays sticks, it's possible to get the situation you described.

Peter.