Crate G-20: "input" produces no sound, but plugging guitar into footswitch does

[Kenrod]

I can see where that would be possible (only when closing the SCG switch) as it is an input to IC2 (pin 2).

I'm trying to figure out why the regular input isn't working. IC1 has 20V at pin 8, only .5V at pin 3 (going through the 300k res. that sound right?).

Per the test specs on the schematic, I'm getiing 21VDC on pin one, should be 11VDC (test point 1, no signal, drive. level & volume on "10").
I used my meter, not my scope. That should be OK right?

Should I just swap out IC1, assuming there's a problem in the "A" half?

Thanks, Kenny

[Enzo]

Not yet. Get the 11v on pin 3 where it belongs, instead of half a volt. it could be the IC itself loading the 11v down, or you could have an open R2. Is there 15v on the top end of R2? Look lower right for R30, R31. They form the 15v reference from the +20v. Is the 15v there? Or is r30 open? (or a trace might be broken)

You can pull the IC and check the pads, is there 11v now on the input pin? little op amps like that only cost like 40 cents, so...


I bet if you pull the guitar cord half way out of the FS jack to the "first click", I bet you also get sound as long as the reverb is turned up.

[Kenrod]

I do have 15V on "top" of R2. I have several 4558 ICs so replacement is not a problem.
I do remember pulling the cable and having sound when the plug was about halfway out, but I don't recall having the reverb up though (think it was off).

[Kenrod]

Swapped out IC1 (4558) and clean channel works though input jack. I now have 11v at pin 1 and 3 (no input signal).
Feels fixed to me. Now to put the chassis back in the cabinet.
Thanks