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Peavey Special 212 troubleshooting

Started by Amestech, June 19, 2023, 06:35:29 PM

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g1

Check R120 and it's connections.  Measure resistance from that 1.5V line to ground.
The 2SC1730 basing is ECB, the BC547 basing is CBE.  Otherwise it should be ok as sub.

Amestech

I think I've got it figured out. I measured from chassis to preamp ground and it read 12.something volts. The preamp ground section was isolated from the chassis. I grounded the jacks with alligator clips and I got my bias voltages correct. Preamp is now making sound through the clean section, have to do further testing once I resolder the wires for the input jacks (for like the third time. These ribbon cables suck). Only thing I'm not seeing is where the preamp would ground when it's all bolted up. These jacks are plastic, so they won't ground when bolted in.

Also, I was planning on wiring in a switch to access the lead/ultra channels without the footswitch. What's the best way to achieve this? I think the footswitch just grounds pin 2 of that 9 pin jack, is that correct?

Thanks for all the help, this is the most complicated amp I've worked with so far. My last solid state was a sunn concert lead, much more simple.

g1

Peavey uses several methods to connect circuit ground to chassis.  Sometimes jacks, sometimes pot brackets, sometimes the screw posts touch a trace or wire jumper.
Partial or full disassembly of any unit can result in lost connections, it can be quite complex in some of the more modern stuff, for example some Yamaha mixers.

I guess there is a panel switch to select between clean/dirt channels and you want to toggle between lead and ultra?  Then yes, grounding FS jack pin 2 will do so.

Amestech

Quote from: g1 on July 02, 2023, 01:58:51 PMPeavey uses several methods to connect circuit ground to chassis.  Sometimes jacks, sometimes pot brackets, sometimes the screw posts touch a trace or wire jumper.
Partial or full disassembly of any unit can result in lost connections, it can be quite complex in some of the more modern stuff, for example some Yamaha mixers.

I guess there is a panel switch to select between clean/dirt channels and you want to toggle between lead and ultra?  Then yes, grounding FS jack pin 2 will do so.

That's weird thing, I don't see any of that on this board. The phone jacks are plastic, and where the pot brackets would solder in have no traces to them. Only thing I can think of is that solder would purposely spill over to hit a ground somewhere. In the schematic, the only chassis grounded points in the preamp are at those phone jacks, so I'm confused on that front. I have omitted the pot brackets because don't fit the pots that I installed. I might have to wire something in.

And thanks for the info on that channel switching. No idea why peavey designed it like that.

Amestech

Update. Ground issue solved. R150 popped. Missed that little piece of the schematic hiding in there.

joecool85

Quote from: Amestech on July 02, 2023, 06:15:52 PMUpdate. Ground issue solved. R150 popped. Missed that little piece of the schematic hiding in there.

Glad to hear it!
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