Mesa Boogie F100 Output Issue

[mikeboone]

I am unable to locate a schematic for this amp. I also did a search for F100 to see if this was covered, no joy.

With a guitar plugged into the input, there is no output. With the guitar plugged into the Effects Return there is a moderate, expected output.

I had a Single Rectum Fryer that did the same thing and it turned out to be one of the J175 transistors in the channel switching circuit.

Does anyone know what the reference designator for the muting transistor is in this amp?

That's my first thought.

I checked all preamp tubes, sockets and they all have what looks to be expected voltages. Would need a schematic to get much further, I think.

[52 Bill]

How many jfets are in this thing? I always check for the mute to be at the input of the power amp.

[g1]

I don't think the boogie schems. show the component designations anyway. So check around the appropriate area like 52Bill said.
Easiest check for a mute fault is to just remove it. If it clears the problem either the Fet is bad or it is not getting it's proper control signal.

[Jazz P Bass]

Mesa Boogie F100 schematic

I am attaching the F30 schematic.
As the F100 uses a quad of 6L6's & 4 preamp tubes, it will understandably be different.
(The F30 uses 2 EL84's & 2 preamp tubes.)
Hopefully, the switching circuitry is the same.

[mikeboone]

update:

I found that by turning the volume way up and hitting the string hard the attack overcomes whatever is plaguing this thing and it gets very loud. But it decays as quickly as it comes up. There are a 8-10 transistors in this thing. I'll try to get a pic uploaded.