Working on a Yamaha YTA-95. I've got everything functioning except that the Speed/Intensity controls for the Wah/Tremolo have no effect. I can hear the Wah filter, but it doesn't oscillate or vary in intensity with controls.

I've re-capped the effect control board and the wah board. Tested the two transistors and JFET on the control board. Any ideas?

Picked-up a Peavy Rage 158 that wasn't working right for another fellow. Found a cold/bad solder joint which fixed a board wiggling cut-out issue. Now everything works fine for a couple of minutes, then no sound. Cycling the amp power brings it back, just off long enough to hear the "turning off pop" then back on, so that tells me maybe not a heat issue as it wouldn't have cooled that much, but is perhaps after a cap discharge? Any ideas of where to start?

Anyone have (and willing to part with) or know where I can get a couple of these wacky 70's Yamaha knobs from a YTA-95? Or know some other amps that used them?

I picked up an MG30DFX, for free actually, because it had intermittent issues for the previous owner and they got fed up. I've read it's most likely an weak power supply.

This thread folks recommend replacing the power caps and the transformer.

http://www.marshallforum.com/index.php?threads/marshall-mg30dfx-problem-volume-fade-instability.36882/#post-1346279

The caps are no problem, but I can't find any specs on the transformer. I don't have much experience with transformers specifically, the markings are sparse and I can't find a part number. Obviously it's not the best amp, but would be nice to have to take places where folks might abuse it. Any idea what would be a good upgrade for the transformer in this amp?

http://www.amparchives.com/Amp%20Archives/Marshall/Schematics%20&%20Layouts/MG%20Schematics/Marshall%20MG30DFX.pdf

Heyall,

Came across this old thread,

http://www.ssguitar.com/index.php?topic=3575.0

While trying to repair an '81 JC-120 I purchased as-is and seems folks in these forums can probably help.

The schematic is here,

http://music-electronics-forum.com/attachments/30030d1407958634-sm_jc-120_11016.pdf

CH1 speaker is dead, when I connect a good speaker to CH1 I get a tone but no signal, seems like around 100hz. CH2 works fine, so, everything works except for CH1 and thus Chorus because it requires CH1. Any ideas what I should be checking? I've got some experience with electronics, amps and pedals, built amps from kits and small ones from scratch. Have an older oscilloscope, multimeter and such. Thanks.

Update: Okay, found a couple of bad resistors (R72, R73, R74) and a bad diode (D1) on CH1 and swapped those out, now I get some crackling from that channel but no signal.

Update: Seems like R75 and R76 are bad too, which are fusing resistors -- I suppose I could replace those with non-fusing ones for now?

Update: Replaced R75 and R76, still just crackling from CH1, but softer.