used C84 DOA.. help!

[alfunko]

I recently picked up a chassis and pre-built C84 module (v 1.9.1) on ebay for a hell of deal, and found that the C84 module, of course, didn't work.

upon asking the seller of how he had it patched in to his system, he informed me, "hey, I'm no techie, I just hooked it up to my marshall half stack, like you would with any other pedal"

yeah.. wow.

I don't have a baseline for how this preamp sounds, being that it was DOA, but at the moment, but I've definitely heard a blown mic pre in my day.

so, on to my troubleshooting dilemma..

I'm guessing this thing had some harsh input levels slammed into it.
what components would've likely taken the hit from a hot input?

symptoms:

low output
distorted
very thin sounding


as per the assembly instructions, I've set the regulators for 18v
I have a reading of 12.1v at R8-R9 junction


U1 power reads:
12v at pins 2,3,5,6
-18v at 4
+18v at 8
0v at 1 and 7

[tpryan]

You can see a schematic here: http://www.seventhcircleaudio.com/C84/C ... 84_sch.pdf

U1 voltages look good. What do you measure at U2? How about pins 2 and 3 of the output XLR?

[alfunko]

You can see a schematic here: http://www.seventhcircleaudio.com/C84/C ... 84_sch.pdf

U1 voltages look good. What do you measure at U2? How about pins 2 and 3 of the output XLR?

U2 reads:
12.2v @ 1
0v @ 2, 3, 5, 6
.07v @ 7
-+18 @ 4 and 8

voltage on output pins were at .20v when I measured, and then I watched it steadily drop to .10v over a period of 20-30 seconds

U3 :
.03v on pins 1 and 7
-+18v on 4 and 8
0v on all others

[tpryan]

Q1 and/or Q2 are probably damaged. Replace with MAT12s if you can't find LM394s.

[alfunko]

Q1 and/or Q2 are probably damaged. Replace with MAT12s if you can't find LM394s.

so, I've replaced Q1 and Q2 with fresh LM394's and sadly, I've got no change... any other ideas?

[tpryan]

We'll need to see it. Send an e-mail to rma@seventhcircleaudio.com for return instructions.