peavey cs800 1/2 not working

[stan]

I have an older(mid 80's?) Peavey CS 800 power amp that has only 1 channel working(1/2 of power amp). does anyone know where I can get schematics or at least where I should start looking for the problem?

[Mark Black]

Peavey is traditionally happy to mail or email schematics:
http://www.peavey.com/support/contactinfo/

Be sure to let them know any pertinent serial number and date code info as there have been many revisions of the CS-800.

Those things are pretty rock-solid. When they do develop a problem it's usually just one or two shorted power transistors rather than the whole bank like in so many other amps, and the damage usually doesn't extend "upstream".

Be sure to retouch the solders at all the power transistor socket pins - a typical place for cracking.

[Enzo]

Or parts@peavey.com Yes, there were several versions, so look on the serial number plate and see if it says CS800 series c, or series b or "zener" even.

If you are not blowing fuses, there is a four pin Molex connector to the power amp module for each channel. Check it out and see if any of the pins on it have spread and lost contact. usually shorted power transistors will pop the fuse.

[amptech]

Originally Posted by stan

I have an older(mid 80's?) Peavey CS 800 power amp that has only 1 channel working(1/2 of power amp). does anyone know where I can get schematics or at least where I should start looking for the problem?

Hi there,

The peavey cs 8oo power amplifier you have is it the old type 3u one!
ie, when you remove the to cover you can see two large heatsink's with 24 o/p tansistors facing upwards, and two large blue 15000uf on the left. If so these amps are easy to service having repaired them before and replacement part's can be pricey. Repair tip you can use the good channel to help fix it and power the board's on lower supply rail of 30v dual rail. if you need more help I'll be gald to help.
cheers for now amptech.

[patpend]

Hi All,

I also have a CS-800, the 3U version as amptech describes, s/n 5A-02115255 with the same problem - one bad channel. It had been working fine 'til one day we turned it on and the right channel was dead, with the red clipping LED constantly lit.

I narrowed down the problem to the driver board that piggybacks on the power transistor board. This board has two #s on the foil side, 111779 and 98808039.

My plan is to start by replacing the five electrolytic caps on this board, but if anyone's got a better idea, or a schematic, I'm all ears.

Thanks, Russ aka PatPend

Originally Posted by amptech

Hi there,

The peavey cs 8oo power amplifier you have is it the old type 3u one!
ie, when you remove the to cover you can see two large heatsink's with 24 o/p tansistors facing upwards, and two large blue 15000uf on the left. If so these amps are easy to service having repaired them before and replacement part's can be pricey. Repair tip you can use the good channel to help fix it and power the board's on lower supply rail of 30v dual rail. if you need more help I'll be gald to help.
cheers for now amptech.

[Enzo]

Well, I'll say the five caps on the board are far less likely to be the problem than all the transistors and diodes. Schematics are given on request from the factory. See the address in post #3 above or the one in post #2. You were reading the whole thread I hope.

Generally on these old warriors, an output transistor or two goes and it blows fuses. Watch the four wire molex connector to each modlue, the pins eventually loosen. Check the output terminal posts - are they shorted together? Sign of a shorted output protect triac.

[amptech]

Hi russ,
Did you compair dc voltage's between channel's at the o/p end? a balancned o/p stage should be below 1 volt! use a 100w bulb to drain the main filter cap's after switch off.
cheers for now amptech.

[patpend]

Peavey graciously provided schematics for the CS-800 series A and B (circa 1977) - these show a single op-amp on the driver board. Unfortunately I have a later series which has two op-amps on the driver board which probably implements the DDT compressor function.

I pointed this out to Peavey and they emailed back the same two schematics

Luckily the other channel working so between that and having the schematics FWIW hopefully it won't take tooo long to figure it out.

Thanks for the help.

[Dave Curtis, dB AudioTech]

I agree with Enzo. It's usually a semiconductor somewhere. When you find the bad device, check the surrounding circuit to see if it took anything else out (bias resistors, driver circuit, etc). It's not uncommon for a fault to damage things "upstream.

I likely have the schem you want. Is it a CS800S or X?

[patpend]

Originally Posted by Dave Curtis, dB AudioTech

.. I likely have the schem you want. Is it a CS800S or X?

I believe it's a CS-800 Series "C". Here are some pics:

The front of the unit:


The back panel:


The boilerplate:


View of the driver board in question mounted on its output board:

[Mark Black]

Did you swap driver boards to narrow the problem down to the one in question? If so good on ya'.

I would start with both driver boards removed and side-by-side on the bench (better mark that bad one). Then using a meter set to "diode test" compare forward & reverse readings on each semiconductor between boards until you (hopefully) find a difference. That goes for the 2 IC's as well - or you could swap just them before removing the driver boards to see if the problem follows.

Bear in mind while checking components that Peavey uses a lot of what look like 1/4 watt resistors but are actually capacitors. They are usually the ones with the more greenish-colored bodies.

[patpend]

Looks like the 6531 is shorted. Anyone know a good place to buy replacements (i.e places that don't charge $12.00 to ship a $0.23 transistor that weighs 0.2 grams?)

[Enzo]

Where are you? PV will sell parts direct, and shipping is included in the price as a rule.

The MPS6531 is a generic part and should be available from Allied or Mouser. All the PV xstrs cross to generics, mostly old Moto numbers. And those can be had reasonably from Allied.

The CS800 S and X models are a lot later. The S has the switching power supply. And the X is one of the "wind tunnel" designs.

[patpend]

I got a 6531 for $0.08 from Mouser, with $4.79 shipping. Not bad. Except that after replacing the shorted one, the channel still does not work. I have the correct schematics now, so back to the workbench I go...

[patpend]

It's all fixed mates! Bottom line, I ended up having to replace:

On the driver board:
Q7 MPS6531 (shorted)
CR13 & CR19 1N4148 (shorted)
R22 47kOhm (open)

I also replaced R22 on the other (working) driver board, because it measured 88k!

On the triac board:
Q1 SAC187 (shorted) - replaced with a MAC224

Thanks to everyone for their support. Special shout-out to amptech for all his help. You guys rock!!

Best regards,
Russ aka patpend

[Mark Black]

Glad to hear you got to the bottom of it, and thanks for posting the results - I always like to think such things will help somebody someday...

[Jose8a]

hi Stan I?m looking for CS 800 PEAVEY SCHEMATICS, (the old one model) is the first time i enter in this page, and is difficult for me because i don?t speak english very well
so i don?t know if you can help me with this.
or how can i do a question that is seen by all in this page?

Originally Posted by stan

I have an older(mid 80's?) Peavey CS 800 power amp that has only 1 channel working(1/2 of power amp). does anyone know where I can get schematics or at least where I should start looking for the problem?

[Enzo]

Hello Jose, welcome to the forum here.

This thread is over a year old, you could start a new thread for your amp if you like. You will get more response that way.

Peavey will send you the schematics if you ask them. send an email to repair@peavey.com or parts@peavey.com

When you contact them, include the amplifier serial number. That will help them select the correct drawing.

[amptech]

Hello,

use your 'good channel' to aid you in fixing the faulty side, start by checking and testing the o/p transistors for short's, don't forget the crow bar trac at the o/p binding post for short circuit. resolder poor joints on the driver pcb and check all connection pulgs as they do work lose.

cheers for now,

amptech

[Gtr_tech]

I've seen the header connectors on the driver pcb cause problems. Be sure to inspect those closely as they are prone to cracking loose from the board.

[guitar620]

Hi people
Recently had one of the above amps for repair, with one channel dead.
Was the 1989 model, with white writing on the front, a wind tunnel, large label on top showing crossovers and non-switchmode powersupply.
There were no shorted output transistors or blown fuses.
Both speaker protection relays dropped in when switched on.
When measured with no speaker connected, there was a small dc voltage across the speaker terminals of some 110mV. This rose up to 360mV after 10 minutes of being switched on.
No audio signal was getting through the faulty channel.
Fault turned out to be resistor R79 on the vertical pcb of the relevant channel - it was completely open circuit.
This is a 33k - 1/2 watt reisitor, in the constant-current source circuit of the front-end "differential pair". (associated with transistors Q18 & Q22.)
It seems to lead a fairly hard life and is better replaced with a 1 watt component.
Hope this info helps someone else with same problem.

Cheers Guys

[bnwitt]

Just as an FYI to anyone finding this thread who is working on a CS 800. I just finished repairing one that had a problem in channel A but a good working channel B. The symptoms were a very low distorted output on the problem channel, clipping light flashing or solid all the time (unless the level control was turned completely clockwise or off) and the power board getting very warm on that channel.

The problem turned out to be a shorted triac on the channel A triac board. This was determined by first swapping the power/driver board assemblies and then the input boards one at a time across the channels while observing that the problem stayed in Channel A.

I then disconnected the triac board on channel A. At that point, the clipping LED stopped flashing through the full stroke of the level control and the overheating of the power transistors stopped as well. This was all done with a signal injected into both channels for comparison.

As Amptech explained to me, the triac board is a crowbar protection circuit which shorts the output circuit in the event of a speaker overload. Funny that Peavey didn't put a fuse in line with this safety (like in a typical crowbar protector) to disconnect the output circuit and prevent potential collateral damage.

Just thought I would share.

[amptech]

Hey Barry,
Glad all worked out in the end and your amp is up and running ok.
There's room in there to add fues's in line with each supply rail to the power pcb just for safety. Them old monsters run for ever with a good service, better then cheap china amps of today!

Best of luck.

[bnwitt]

Amptech your help was invaluable in directing me to the problem. Thanks again for sharing.
Barry

[otherdreams]

Hello!

I've got a CS-800 from 1983. Channel B works great, but Channel A is passing no signal.

When I got it, it blew a fuse immediately. I removed the power transistors from Channel A to test them, and found several with shorted terminals. So, I replaced those.

It blew another fuse. After swapping all of the sections of Channel A and B for testing, I found the Triac board and removed the Triac (SAC187). Now it powers up without blowing a fuse.. but Channel A passes no audio to the speaker output.

Also, the "output clipping" LED lights up when I give it reasonable input signal while Channel A's volume pot is turned up 1/4 of the way or more.

I assume this means there's probably DC on the audio output(?)

Can anyone recommend some likely causes / solutions?

Thank you!

-Robert
[ quietchannel.blogspot.com ]

[amptech]

Hello Robert,

I've posted many comments on these amps all with same fault blowing it's fuse.

If there's a 'good' channel use it as a ref point to take voltage readings and compare these readings to the bad channel.

watch out for loose connections poor solder joints and them triac crow bar circuits that drives folk nuts

Do you have a scope/sine genertor has they will help you track down the fault faster and save you some time. Don't for get do a quick dc offset test with no load. You can use a speaker test load made up with a resistor of say 6.8 ohm 100w or more per side.

[tcs30]

peavey cs-800 c series amp




ok this is my first time being here, and hope i can get some help.

i got a peavey cs-800 c series amp. one channel is out "B" channel. the clip light stays on all the time with no sound out that channel. now i kinda of a novice to electronics, i know some but not alot. i had one of these amps do this same thing to me before, and seen it blew one of the big blue caps inside 15000mfd at 90volts, i replaced it and it worked. but this one doesn't show any sign of the caps have gone bad. so the only thing i have done so far with this amp is i checked the caps, and they both seem to be fine. so now what? can sombody please help me.

[Enzo]

Hi, welcome. May I suggest starting a new thread for your amp? You will get better respons than here at the end of a 25 post run that has been dormant for 6 months. I will say the photos up in post #10 could be useful to refer to in discussion.

The power supply is shared by both channels. if it were screwed up, neither would work right. Whatever you have going is in the channel.

Look on the volume control for the bad channel. Isn;t there an op amp on the little board? It is in a socket, isn;t it? Try a new one, or swap it with the other channel's. If the problem moves with the IC, it is bad.

The power output stuff is probably OK, or you'd likely be blowing fuses. The driver card on each channel is the same, you could swap driver cards between sides to see if the card holds the problem.

We need to isolate the problem to solve it.

[jrfrond]

The triac in those amps is the "sacrificial lamb" in the "crowbar" protection scheme. DC on the output will fire the triac, which shorts the mains power and blows the mains fuse, and commits suicide in the process. The triac almost ALWAYS needs to be replaced when there's a short.