Carvin wiring

[Valvehead]

Im working on a DC 400? its got a couple pcb's inside , 9v , 2 hums / 3 mini toggles / 4 pots. 1 pot is push/pull for active/ passive ( i think )

anyone have a schematic of this ?? The passive mode works but not the active mode . The push/pull pot does switch . Cant find the issue yet

[The Dude]

I can't find a schematic, but as I recall, these are passive pickups with a preamp built in? Again, if memory serves, it's built with op amps? If that's all correct, I'd start with checking to see that your 9V is getting to the supply pins of the op amps. Pin 8 of the op amps should be supply and pin 4 ground.

[Valvehead]

I can't find a schematic, but as I recall, these are passive pickups with a preamp built in? Again, if memory serves, it's built with op amps? If that's all correct, I'd start with checking to see that your 9V is getting to the supply pins of the op amps. Pin 8 of the op amps should be supply and pin 4 ground.

yes.
I will check at the op amp

[Valvehead]

All resistors good , caps arent puking..joints good. Jack wiring ok .

heres what i have at the MC33178P chip =
pin1. 3.6v
2. 3.3v
3. 4.4v
4. 0v
5. 4v
6. 3.6v
7. 3.5v
8. 9.0v


maybe bad op amp ??

active mode is super low output , but i can hear it working

[The Dude]

Those voltage look reasonable. I wouldn't suspect the op amp from the voltages. It's going to be tough without a schematic, so just stabbing here. I know some of the Carvin preamps have a trim pot for max gain. Does this one have a trimmer? If so, you might check it.

[Delta362]

Unfortunately I sold my DC400 or else I could have checked some values for you.

[Valvehead]

Those voltage look reasonable. I wouldn't suspect the op amp from the voltages. It's going to be tough without a schematic, so just stabbing here. I know some of the Carvin preamps have a trim pot for max gain. Does this one have a trimmer? If so, you might check it.

yes...checked the trim pot

[Valvehead]

Its fixed------it was a bad op amp