Carvin Legacy 212 problem

[guitardog]

Ok, I was finally able to get back into this amp. I lifted one end of R20 and the noise is still present. If I have time tonight I will remove the reverb pot and see if that does anything.

Thanks again

[guitardog]

I finally got the time to get back into the amp. Today I lifted one end of R20. Noise persists. I went back and removed the reverb pot. Noise persists. Looking at the schematic some more....

[m1989jmp]

I finally got the time to get back into the amp. Today I lifted one end of R20. Noise persists. I went back and removed the reverb pot. Noise persists. Looking at the schematic some more....

Well, that's strange but at least you've narrowed it down now.

As per Enzo's suggestion, check continuity from one end of B5 trace to another, the trace could be screwed up. Also, focus on R21, R20 and C66, and maybe replace them with the same type.

I know it's kind of shotgunning, but the fault is most likely related to one of those components..

[guitardog]

I do believe that we are getting closer. C66 and C67 have been replaced already. I will inspect the traces first, but replacing R20 and R21 seem to the be the next logical move. I should also mention that the effects loop is part of a separate break out board that is attached with ribbon cables. I did resolder all of those joints yesterday, but haven't checked to see if there was a change. What do you guys think? Enzo?

[guitardog]

Update. Resoldering the ribbon cable pins made no change. Quick question. R29 (and others) have a flag on one end with the letter D in them. What does that denote?

Thanks

[m1989jmp]

Update. Resoldering the ribbon cable pins made no change. Quick question. R29 (and others) have a flag on one end with the letter D in them. What does that denote?

Thanks

Most likely nothing special, any 1/4 W resistor will do the job. You may up it to 1/2 watt if the board space allows it.

[The Dude]

Update. Resoldering the ribbon cable pins made no change. Quick question. R29 (and others) have a flag on one end with the letter D in them. What does that denote?

Thanks

That "D" with the flag denotes it's connection to the power supply 385V node. Scroll down to the lower left power supply portion of the schematic and you'll see a corresponding "D".

[guitardog]

Thanks Dude. I was looking all over and couldn't find it. I see it now.

[m1989jmp]

Thanks Dude. I was looking all over and couldn't find it. I see it now.

Wow my bad, thought you were talking about R20/21.

[Enzo]

D in a flag.

R29 needs to connect to a power supply, so look down lower left at the power supply. There is your D, the +385v B+ node.

The D node powers most of the preamp with the C node powering the reverb driver.

The C and D flags are just shorthand. Instead of drawing lines all over the schematic to show power distribution.

[guitardog]

Thanks Enzo. The Dude also answered my question. The way the threads run on here gets confusing so I don't see posts right away. So R20 is still lifted, the reverb is (and has been) disconnected, the reverb pot is currently removed. I have inspected the traces but can't see anything obvious. Noise persists until a connector is plugged into the send (or return) jack. Noise persists if the loop is jumpered. If I am reading this correctly, the signal path is broken with R20 lifted and everything to the left, including the relay is eliminated. With the reverb pot removed, B5 circuit is broken as well. C66, C67 and Q5 have been replaced. In my mind that only leaves R21, R29, R82, R83, R65 and the H5A connector out to the send jack as suspect. Is it correct that B1 is the signal path when there is not a cable plugged into either of the effects loop jacks? If so, I think that I should lift C67 next. If the noise is eliminated, it would rule out the H5A connector and the break out board that the effects loop and other jacks are mounted to. Thoughts?

[guitardog]

Actually, we have already established that removing Q5 eliminates the noise. Would that rule out R65 or R29?

[guitardog]

Wow my bad, thought you were talking about R20/21.

All good. I appreciate the help!

[The Dude]

You removed the reverb pot (if I recall) and noise was still present. That eliminates any noise coming in from the reverb return circuit. You shorted across R21 and the noise went away. That eliminates Q5 circuit and anything past it. You lifted R20 and noise still present, so it's not coming from the relay or reverb send side. You changed C66 and noise still present. IMO, the chief suspect is R21 given this information. I'd try changing it.

[Enzo]

I would also get a Qtip and some alcohol, and seriously clean all along any trances connected to that Sensitive R21 spot. Nothing visual may be there , but we still can have contamination.

I thought we already changed R21. If not, certainly do that.