Peavey CS-800 Series C

[tjsilva]

Thanks Enzo, I tried to measure voltages this evening and I get 120 from the fuse to the thyristor and from the thyristor to one side of the switch but no power on the other side of the switch with the switch on. When I first started to check out the amp the fan was disconnected I tried using the schematic to hook it up but I think i may have hooked it up wrong. I emailed Peavey to ask them if the have a diagram of the terminal wiring so I know for sure where the fan should go, I have since disconnected it again. Any ideas on the power could it be just a bad switch? Any steps you could provide would be much appreciated.

[Enzo]

Look at the schematic, the switch does not switch mains voltage on and off to the power transformer. There is a large triac in the bottom of the amp chassis that does that. The panel switch only controls the gate of that triac. I guess you know that already.

Power down, and unplug from the wall. The switch should have a wire from the gate of the triac - the gate is the small post - and there should be a resistor to the other terminal. Shcematic says 22 ohms, but other values are possible. Disconnect something to isolate the switch, and check its operation with an ohm meter.

Dies your power switch have 4 terminals or 6?

[tjsilva]

Thanks Enzo I have six terminals on my switch, the middle two have a resistor across them. I am at work and will check the switch tonight. I should have thought to ohm out the switch last night, but I guess my brain doesn't function as well late in the day after working two jobs. I looked up how to test the triac as well and will try that tonight, triac not thytistor as I previously stated again end of the day. Thanks Again I love doing this stuff and it also allows me to get equipment for my sons band for cheap. You guys have already helped me fix my peavey supreme amp head.

[Enzo]

Not to worry, triac is one kind of thryistor. Nothing wrong with calling it that.

I see, what they did then was run wires to the two end terminals and the resistor across the middle two. SO when the switch is on, the wires are connected to the resistor, completing its circuit. The other two end wires are for the light within.


Those big triacs are pretty reliable, but they can fail. Usually they fail shorted, which does nothing more than leave the amp always on, have to unplug it to power down. Doesn;t hurt anything. The other end of the scale is an open triac, which means no power.

The triac has three terminals, the small one is the gate. If you pull the wires off the two large terminals and short them together, then that leaves the amp always on, and that is fine for servicing and further troubleshooting. Make sure they are joined securely and safely - they should be taped or something.

[tjsilva]

Enzo I believe my switch and the triac are fine. One thing I did find tonight both my outputs are shorted which from I have read means the two triac boards have shorted. would this prevent the amp from powering up? I only got a chance to pull one triac board off, the transistor on the board has the middle leg cutoff and the other two are shorted. they also weren't soldered or came unsoldered. Thats all I have time for tonight as always and advice on next steps greatly appreciated.

[Enzo]

The middle leg is cut off because they are using the tab for that connection.

A shorted SAC187 output triac is a good sign that you have bad transistors on the power modules. They rarely fail on their own.

I am having a discussion with someone about a CS800 power up issues over at the Peavey forum. PV web site, find the forums, power amps section. You might find the thread useful.

You need to find the 80v across the two big filter cap cans. If that is there, then your mains wiring is working. If not, then we look for mains voltage at the transformer primary. Each power module has a thermal breaker on it - the twisted blue wires - the two of those are in series with the mains, so a open sensor, a broken connection or a wire off one will prevent power up.

SHorted output triacs won't prevent power up, but they might well blow the main fuse.

I have attached the switch wiring, but it only shows some of the connections on that long terminal strip. Contact the service department at PV and ask if they have a sheet with the wiring of that terminal strip. If someone got in there and moved a couple wires, you either have to laboriously go through it all with the schematic or have a guide. It can be confusing if someone moved a wire, becuase nothing "looks wrong."

And each power module has a four pin molex on the underside that carried main power rails plus ground and output. Unplug that and the module is efectively out of circuit. That is how I isolate one bad channel. UNplug both and you still can explore the power supply.;

[tjsilva]

Thanks Enzo for pointing me to that forum you where right I now think I know why I cannot power up. My thermal sensor with the blue twisted wires was not connected. Will try to connect those up tonight and let you know. I joined that peavey forum as well and I am going to ask that poster if he can take a pic of the terminal strip especially where the fan connects to. I have asked Peavey about a possible diagram for the terminal strip but they say they do not have one. Thanks again

[tjsilva]

Well my switch still doesn't lght up but the amp is powered up. I had the thermal switch disconnected. I still haven't had a chance to test the good channel but it is holding a fuse with the blown output tranmitter removed Next problem the channel that had the bad transistor now has the clip led always on I guess that would be the next step. I have 80volts dc across the large caps. Any ideas on where I should gom from here?

[Enzo]

Pick a channel, either one, I don't care which. Get that channel working 100%, then go to the other channel. That way we won;t have to keep referring to some description. Leave the other channel unplugged. When the one is fixed, unplug it and plug in the other. Only when we have each channel working on its own will we connect both of them.

You are now holding the fuse? Progress. But the clip light is on? Now is as good a time as any to swap driver cards to see if anything changes. For that matter, check the power supply to the driver. Do the ICs on the card have proper supply voltages at their power pins?

Meanwhile, does it pass signal? DOn't put a load on it yet, but scope the output with signal applied to input. Coming through? No scope? Voltmeter set to AC volts, see if any is on the output.

[tjsilva]

channel b is functional i actually ran a speaker and it sounds great, did that before I saw your post. I swapped the known ggo driver board to channel A and it worked so the problem is on driver board A. How would I measure voltage at the pins of the IC's? positive on the pin negative to where-- ground where is the best place for ground? I will try to swap the ic's to see if the problem follows them.

[The Dude]

Just a little tip for future reference:
On the old Peavey CS's, if you (of course with the amp unplugged or powered off) put a DVM across the speaker terminals on diode check, it should read wide open (it might take a few seconds for caps to charge/discharge). If you get anything else, you have an output/triac problem. This will usually tell you where to look before you even "pop the top".

[Enzo]

Unless otherwise specified, voltages are with respect to ground.

[tjsilva]

Well I blew the good op amp I had by plugging it into the bad driver board. Ordered some replacements, no more wreckless swapping. Enzo is there a replacement for the out put triacs, I can't find the part number anywhere. Once I get back to one good channel I will start measuring voltages on Driver board A, the bad one. Thanks for all your help Enzo.

[Enzo]

SAC187 triac is at the Peavey parts department or an equivalent.

Generic equivalent is 2N6346A (200v 12A TO220) I have 2N6348A in my drawer for them. Any similar rated triac that fires in all quadrants will work.

[tjsilva]

Well got my op amps, I replaced both op amps on both driver boards, I checked all the components on the bad card against the good card and found nothing else bad. Hooked everything up added signal and I get AC from the output. I hooked up a small speaker and tested both channels at low to mid and get sound from boh of them. I am now waiting for my triacs to come in so I can replace the output protection boards and test her a little louder. Also got my fan hooked up with the photo on the Peavey forum Enzo directed me to. Thanks for all the help. I also checked voltages at the input boards op amps and all was well.