Peavey CS-800 Series C

[broot]

Hello,

I've been trying to fix channel B on a Peavey CS-800 and it seems I've triggered the thermal breakers as the high temp pilot light on the front of the unit is on. Channel A also seems to have stopped working. I was just wondering if anyone knew how to reset the breakers and if this would cause channel A to quit. I've attached the schematic Peavey sent me. Thanks.

[broot]

OK false alarm haha. I had accidentally disconnected one of the thermostat clips when I was rummaging around in the unit. Breaker light is now off and channel A is working again. If anybody has any ideas about channel B I would be truly grateful. I've removed the triac board and it seems like the sac187 is good though the 1K resistor on the gate is measuring 50 ohms. Should I just rebuild the triac board or am I barking up the wrong tree?

[Enzo]

Wrong tree, take the same measurements on the triac board for the good channel and see.

Usually the triac is either shorted or it is good. Yours is not shorted.

If anybody has any ideas about channel B I would be truly grateful.

Back at you, if anybody had any idea what was the problem you were trying to fix, we'd chime in. What is wrong with the channel?

Welcome to the forum too.

[broot]

Wrong tree, take the same measurements on the triac board for the good channel and see.

Usually the triac is either shorted or it is good. Yours is not shorted.



Back at you, if anybody had any idea what was the problem you were trying to fix, we'd chime in. What is wrong with the channel?

Welcome to the forum too.

Thanks Enzo. The problem with channel B was that there was no output at all. I swapped the driver boards and channel A still worked but no channel B so I'm guessing it's something to do with channel B's power board but I'm not sure what.

Unfortunately, in the process of trying to fix channel B I've screwed something up in the ac power supply circuit. The pilot light on the power switch stays on and shortly afterwards the fuse pops. I unplugged all the boards from the power supply and the fuse doesn't pop but the pilot light stays on. At this point I'd be happy to just get channel A working again.

Any idea why the power light is staying on?

Thanks again.

[Jazz P Bass]

May I suggest slowing down & taking your time.
Tech induced faults are embarrissing to say the least.
I think you should check Q1 at the power switch.
Q4025P is an alternistor. Two SCRs back to back.
You may find that it is shorted.

[km6xz]

There is very little that could cause the light to stay on...other than a mis-wiring(wired lugs put back on the wrong terminals) or a leaking triac Q1 that is turned on by the power switch.
Before the AC mains side of the power supply stopped working correctly, was the fan working and does it run now?
By swapping the driver boards you have reduced the vast range of possible faults: the power supply, connectors or output transistor power board is pretty much it.
Had you been able to do any voltage checks on the power output board before the latest problem arose? This amp has a crowbar protection system that detects a DC offset and shorts the speaker-out line.

[broot]

May I suggest slowing down & taking your time.
Tech induced faults are embarrissing to say the least.
I think you should check Q1 at the power switch.
Q4025P is an alternistor. Two SCRs back to back.
You may find that it is shorted.

Haha I am getting a little ahead of myself. As you can tell I'm pretty much new to this. Q1 seems ok.

There is very little that could cause the light to stay on...other than a mis-wiring(wired lugs put back on the wrong terminals) or a leaking triac Q1 that is turned on by the power switch.
Before the AC mains side of the power supply stopped working correctly, was the fan working and does it run now?
By swapping the driver boards you have reduced the vast range of possible faults: the power supply, connectors or output transistor power board is pretty much it.
Had you been able to do any voltage checks on the power output board before the latest problem arose? This amp has a crowbar protection system that detects a DC offset and shorts the speaker-out line.

This is it, thanks! I removed the thermo clip connection that I had replaced earlier to get the high temp light to extinguish. Now the high temp light is back on but the power light is off. The fan runs and I measure 14Vdc on the red/yellow power wires and 30Vac on the same wires. I get nothing on the blue and black wires. I'm going to contact Peavey and see if they have anything about wiring the lug terminals.

[broot]

May I suggest slowing down & taking your time.
Tech induced faults are embarrissing to say the least.
I think you should check Q1 at the power switch.
Q4025P is an alternistor. Two SCRs back to back.
You may find that it is shorted.

Ok I got a wiring diagram from Peavey and when I hooked everything up and turned it on the power light was still on. I turned the power off and went to check the resistance of the alternistor. When I checked MT2 and Gate the fan turned on. I also noticed the readings on the wires that connect to the power board from the big blue caps and saw that the voltage was nearly 300Vac and slowly draining. So I'm guessing the alternistor is definitely shorted.

[broot]

OK after another day of testing and troubleshooting it turned out that two transistors on power board B were shorted and a 6018 on driver board B was toast. I guess the power light was supposed to be on. Quite the learning experience. Thanks for all of your help and patience.

[tjsilva]

I am also working one of these old amps, my switch light does not come on but the fan powers up. Channel A does not work and I found two bad output transistors,waiting for delivery. Could the light on the on switch be as simple as the led switch being no good?

[Jazz P Bass]

I thing Peavey uses a 'pilot lamp'.
It connects directly across one of the power transformer secondary windings.

[tjsilva]

so this light would be in the switch and wired to the transformer output correct? Thanks for the info

[Enzo]

The light is neon and is inside the switch - it is part of the switch.

[tjsilva]

Thanks Enzo, So I probably need a new switch then. Any idea on the part numberfor it?

[Enzo]

You can get it from PV parts by description: lighted rocker switch for old CS800c

There are two types of those. One with four terminals, DPST, and the internal light is across two of them. SO you need to ensure that the mains wires go to the end without the light. Get it backwards and the light is always on, even if nothing else is. The other kind has six terminals. It is also a DPST, but the light is separate, and the two extra terminals are for it.

There are some applications where the light needs to be separately controlled. In fact the fan switch in this amp is one. The fan switch is for fast/slow, but the light in it only comes on when the thermal breakers open.

Either type works for the power switch, but are wired in differently.

PV used to include a sheet on wiring an amp for one when it is wired now for the other. Ask them for that sheet.


Otherwise, go to Mouser or someone like them and get a lighted rocker to fit that hole. Measure the hole in the panel.

If it were mine, I'd ignore the light anyway.