Mark IV low volume problem

[rotaryunison]

Lately, a few times my Mark IV has been acting funny. It works fine for a while, then I'll put it on standby, come back and the volume is extremely low from all channels. Is it simply overheating, or what could this be?

 

[Alivefor5]

I had a similar issue and the problem was the pull pot on the output level control. Cycle that pot (silent recording) in and out about 20 times and see if the problem goes away.

 

[rotaryunison]

OK, the problem has something to do with the effects loop. When the effects loop is off, then the problem completely disappears.

Is an FX loop generally a cheap fix?

 

[MrMarkIII]

Sometimes you can fix this by plugging cables into the send and return jacks and wiggling them around.
(Get your mind out of the gutter).

 

[cb101]

I had this same problem about two weeks ago with my Lonestar. Go to standby for a while and then go live and the volume was way down and then off all of the way. Flip the switch to hard bypass and then everything was alright. I changed out V3 and V5 thinking the problem was either in the FX loop driver or PI. I always have something in the loop so the jumper fix was already done. I got to thinking what was different in my setup. About a week before I had put in some new power tubes-Winged C's. I switched back to the stock Mesa's and the problem has not returned. It doesn't make any sense that the power tubes would cause this problem but in my case they did.

 

[satisfied5582]

maybe you needed to rebias? that is what i was thinking, even though mesa has a fixed bias. i had a none mesa amp that needed rebiasing and the volume would be low right after i switched the stand by switch, but after about 15 minutes it was back to normal. the guy that does all my amp work said it needed rebiasing. so i did, and no more problems. just a thought since you swapped tubes.