Peavey CS800 speaker output ?

[gtrplayr1976]

Thought I would start a new thread here. I have this CS800 on the light bulb limiter , I am reading same voltages on both channels on the output boards ( right now -38 ,and + 38) Checking at the speaker outs I have -3.4 MV on one channel ,and + 6.9 on the other. What might I be looking for here ? Need more info ?

Thanks a heap, Tom

[Jazz P Bass]

Is that +6.9 volts or mv's?
If it is mv's, then I do not see an output device failure problem.
Is the lamp burning brightly (not so good) or did it glow at capacitor charge up & then go dim?(this is good)

[gtrplayr1976]

Sorry..that's mv. Glowed bright on charge then dim. Would the difference in the two be an issue if the other is - 3.4 mv ,and the other +6.9 mv . I'm just not sure how to tell which channel is working. I was told one side doesn't work. Rail voltage is low ,but the same on both channels ,and I have the limiter hooked up.

Thanks Jazz

[gtrplayr1976]

OK..so I've found Q7 bad on one driver board...not sure about other components yet.

[Jazz P Bass]

Positive Limit transistor: MPS6503.
Check the diodes around it & Q6.
If that is all that is wrong, get rid of the lamp limiter.
Your voltages will come up.

[gtrplayr1976]

Positive Limit transistor: MPS6503.
Check the diodes around it & Q6.
If that is all that is wrong, get rid of the lamp limiter.
Your voltages will come up.

Thanks Jazz. Everything else seems normal. Just the one transistor. I happen to have another PV parts amp with some of those on it, so hopefully just a swap.

[Enzo]

Voltages are low with the bulb in place? Well yes, the resistance of the bulb is in series with your transformer.

Once we know the amp is not going to blow fuses or burn up, get rid of the bulb. That is the purpose of the bulb, to let you power up without burning up the amp if it is still shorted. out. It is not intended that the amp will operate normally with the bulb limiter in place.

A few millivolts on the output is nothing, ignore it.

How do you tell which channel is working? By connecting a speaker and applying a signal. You were "told" one channel didn't work. WHo says that report is correct? We need to find out. I as a repair shop often see things brought in with "bad channel" problems only to find the unit works just fine and the problem was they had a dead output on their mixer.

[gtrplayr1976]

Voltages are low with the bulb in place? Well yes, the resistance of the bulb is in series with your transformer.

Once we know the amp is not going to blow fuses or burn up, get rid of the bulb. That is the purpose of the bulb, to let you power up without burning up the amp if it is still shorted. out. It is not intended that the amp will operate normally with the bulb limiter in place.

A few millivolts on the output is nothing, ignore it.

How do you tell which channel is working? By connecting a speaker and applying a signal. You were "told" one channel didn't work. WHo says that report is correct? We need to find out. I as a repair shop often see things brought in with "bad channel" problems only to find the unit works just fine and the problem was they had a dead output on their mixer.

Thanks Enzo. Can i just use a guitar , and connect it to one input at a time, and do the same with a speaker on the output? I did notice one thing with the triacs on the speaker outs. One of the resistors is supposed to be 1k ,color bands show that , but one on channel A reads 39 ohms ,and one on B reads 56 ohms. I have the circuit boards out.

[Jazz P Bass]

Is there a chance that you turned the triac on when you where measuring.
Normally, a triac is off.
If in doubt, remove the triac & retest the 1K resistor.
You can now test the traic out of circuit too.

[gtrplayr1976]

Is there a chance that you turned the triac on when you where measuring.
Normally, a triac is off.
If in doubt, remove the triac & retest the 1K resistor.
You can now test the traic out of circuit too.

I removed both boards. The resistor was fine when I pulled one leg . I wouldn't have known if I turned on the triac. I did notice on the B channel that the nuts that hold the Triac on were loose. One was backed nearly all the way off. I'm going to pug it up ,and check it.

Thanks Jazz

[Enzo]

As they are wired on the board, if the triacs do not seem to be shorted across the output, then they are probably just fine. That is all I look for, shorted or not.

You can use any signal you like, as long as it is enough to make the sound come out. A guitar is fine, though it ties up your hands. A Shure SM58 wouldn;t work well because the signal is so weak. I have a small stereo receiver on my bench to listen to a local FM station, and I have a cable plugged into the back of that, and I use the signal from that (REC OUT on the rear panel) as a general test signal. I'd rather listen to music than test tones. Got a CD player? I have a signal generator if I really need a clean signal for scoping or distortion tests. Somewhere around here we have a cheap little Yamaha keyboard - like you might find at K-Mart this time of year. It makes a reasonable test signal. I can play notes, or trigger its little demo tune. Sit my roll of solder on one of the keys and I get a continuous note. And when I am just looking to see if an amp channel even functions, a lot of time I do nothing more than touch the input with my finger, and the resulting hum or lack of it tells me the amp is functioning.

[gtrplayr1976]

As they are wired on the board, if the triacs do not seem to be shorted across the output, then they are probably just fine. That is all I look for, shorted or not.

You can use any signal you like, as long as it is enough to make the sound come out. A guitar is fine, though it ties up your hands. A Shure SM58 wouldn;t work well because the signal is so weak. I have a small stereo receiver on my bench to listen to a local FM station, and I have a cable plugged into the back of that, and I use the signal from that (REC OUT on the rear panel) as a general test signal. I'd rather listen to music than test tones. Got a CD player? I have a signal generator if I really need a clean signal for scoping or distortion tests. Somewhere around here we have a cheap little Yamaha keyboard - like you might find at K-Mart this time of year. It makes a reasonable test signal. I can play notes, or trigger its little demo tune. Sit my roll of solder on one of the keys and I get a continuous note. And when I am just looking to see if an amp channel even functions, a lot of time I do nothing more than touch the input with my finger, and the resulting hum or lack of it tells me the amp is functioning.

CD player...that'll work...never even crossed my mind. I only have one speaker though 4 ohm 15".

[gtrplayr1976]

As they are wired on the board, if the triacs do not seem to be shorted across the output, then they are probably just fine. That is all I look for, shorted or not.

You can use any signal you like, as long as it is enough to make the sound come out. A guitar is fine, though it ties up your hands. A Shure SM58 wouldn;t work well because the signal is so weak. I have a small stereo receiver on my bench to listen to a local FM station, and I have a cable plugged into the back of that, and I use the signal from that (REC OUT on the rear panel) as a general test signal. I'd rather listen to music than test tones. Got a CD player? I have a signal generator if I really need a clean signal for scoping or distortion tests. Somewhere around here we have a cheap little Yamaha keyboard - like you might find at K-Mart this time of year. It makes a reasonable test signal. I can play notes, or trigger its little demo tune. Sit my roll of solder on one of the keys and I get a continuous note. And when I am just looking to see if an amp channel even functions, a lot of time I do nothing more than touch the input with my finger, and the resulting hum or lack of it tells me the amp is functioning.

Enzo , I had to use a guitar ,but I did get sound from both channels. It just doesn't seem very loud. Is that normal ?

Thanks , Tom

[Jazz P Bass]

Enzo , I had to use a guitar ,but I did get sound from both channels. It just doesn't seem very loud. Is that normal ?

Thanks , Tom

O/k, please bear in mind that the CS800 is a power amplifier.
THe input sensitivity is +3dBv (1.4Vrms) into 20K ohms for rated power.
Think Cd player or a mixer board.
A guitar can typically achieve 100mv's.
That is a wee bit short of 1.4V.
Personally I would test the amplifier into a dummy load, hooked up to a scope, with a proper signal amplitude.

ps: here is the link to the complete manual: http://www.peavey.com/media/pdf/manuals/80300991.pdf

[gtrplayr1976]

O/k, please bear in mind that the CS800 is a power amplifier.
THe input sensitivity is +3dBv (1.4Vrms) into 20K ohms for rated power.
Think Cd player or a mixer board.
A guitar can typically achieve 100mv's.
That is a wee bit short of 1.4V.
Personally I would test the amplifier into a dummy load, hooked up to a scope, with a proper signal amplitude.

ps: here is the link to the complete manual: http://www.peavey.com/media/pdf/manuals/80300991.pdf

Thanks Jazz , good idea , but I have none of those things..lol..So would you say there is a chance one , or both channels may still no work even though I did get sound from both, and volume changed as I increased the setting ?