Peavey Delta Blues issue

[Leevi]

I'm trying to fix the reverb of the Peavey Delta Blues combo.


http://el34world.com/charts/Schematics/files/Peavey/Peavey_deltablues.pdf


The output side of the circuit seems to work since the amp reacts pretty well when touching the springs.
I have even tried with another reverb pan without success.


How common is it that the IC with the OP amps is broken? The circuit could be changed quite easily.
Otherwise there is very difficult to do any changes.


/Leevi

[shooter]

since the other half is recovery and that works, I'd suspect cables, connectors, no signal getting in, but for $2 you can cut it out, solder in a good socket and a new chip.

got a scope?

[Leevi]

I measured the tank input with scope and there is no signal visible.
I also measured the cable which is OK. There is about -5V DC voltage at the tank input.
/Leevi

[2deaf]

Ground is the positive rail for that 4558 Op Amp and the signal is referenced to -15V.  You might get some funny results if your testing equipment is referenced to ground.  You also have to make sure that the shield on the reverb input cable never has a path to ground. 

 

[Leevi]

I found the cause for the problem. It was probably a bad contact on one IC leg.
After I had measured voltage on the leg the reverb started to work. The IC stays in its socket.
Now also the voltage across the tank input is 0V and the reference voltage towards ground -15V which sounds right.


/Leevi

[shooter]

probably a bad contact on one IC leg.

when I 1st started fixing CAT scanners, the system I started on was basically an R&D system, everything in the "front-end" was socketed IC's while permanent boards were being made. 90+% of all the problems were fixed by taking the "bad" board out, laying it on a hard surface and pressing down on ALL the IC's, walla, gone fishing