I swear if I dont get this fixed im going to pull my hair out!! lol.
i have fixed this amp 3 times, and now its to the point where im stuck.
im not sure if anyone is familiar with DDT or not, but its weird.
The problem is both channels are really weak and distorted. I can turn the volume pot up by one click, the DDT light kicks in. and the sound is weak. the heatsink gets soo hot to touch, hi temp shutdown kicks in. Both channels are like this.
It was to the point where one channel was like this but the other channel was perfectly fine. I pulled EVERY COTTON PICKEN output transistor off the board, and the driver transistors and tested them. They all tested fine. ok....
put them back into the board, and I pulled the output emitter resistors and tested them, they all tested normal, except for a couple tested 4ohms and they supposed to be testing around .33ohms. I replaced those.
I ran a check on all the transistors and diodes, along wiht resistors on the driver board, and they tested fine. one transistor was shorted, and I replaced it. both channels have little to no DC offset.
I have done everything I can think of. I was curious as to where the problem lied, either in the output board, or the driver board. so one side worked, the other side didnt. I switched the driver boards, and didnt know the transistor on the bad side driver board had shorted again, and as curiousity killed the cat, it ****ed the good side up in the same way as the bad side.
So both channles are doing teh exact same.
I have the PDF of the schematics, but they are too big to post.
i dunno what to do. all output transistors test fine, no reverse leakage, or open junctions, no shorts. nothing. my supply rails are dead on.
i tested the output transistors, and on most transistors, with the DMM on diode check, it measures about .407 from base to emitter, and about .435 from base to collector on about all of them.
collector to emitter was oL, like its supposed to be.
I tested all of these out of circuit.
another thing to note that is weird unlike when it was working, you can hear the distorted sound inside the output bank transistors. they are acting like a speaker. its only doing this now. they never did this when it worked.
Im stuck
i have fixed this amp 3 times, and now its to the point where im stuck.
im not sure if anyone is familiar with DDT or not, but its weird.
The problem is both channels are really weak and distorted. I can turn the volume pot up by one click, the DDT light kicks in. and the sound is weak. the heatsink gets soo hot to touch, hi temp shutdown kicks in. Both channels are like this.
It was to the point where one channel was like this but the other channel was perfectly fine. I pulled EVERY COTTON PICKEN output transistor off the board, and the driver transistors and tested them. They all tested fine. ok....
put them back into the board, and I pulled the output emitter resistors and tested them, they all tested normal, except for a couple tested 4ohms and they supposed to be testing around .33ohms. I replaced those.
I ran a check on all the transistors and diodes, along wiht resistors on the driver board, and they tested fine. one transistor was shorted, and I replaced it. both channels have little to no DC offset.
I have done everything I can think of. I was curious as to where the problem lied, either in the output board, or the driver board. so one side worked, the other side didnt. I switched the driver boards, and didnt know the transistor on the bad side driver board had shorted again, and as curiousity killed the cat, it ****ed the good side up in the same way as the bad side.
So both channles are doing teh exact same.
I have the PDF of the schematics, but they are too big to post.
i dunno what to do. all output transistors test fine, no reverse leakage, or open junctions, no shorts. nothing. my supply rails are dead on.
i tested the output transistors, and on most transistors, with the DMM on diode check, it measures about .407 from base to emitter, and about .435 from base to collector on about all of them.
collector to emitter was oL, like its supposed to be.
I tested all of these out of circuit.
another thing to note that is weird unlike when it was working, you can hear the distorted sound inside the output bank transistors. they are acting like a speaker. its only doing this now. they never did this when it worked.
Im stuck
mbates14 said:I swear if I dont get this fixed im going to pull my hair out!! lol.
i have fixed this amp 3 times, and now its to the point where im stuck.
im not sure if anyone is familiar with DDT or not, but its weird.
The problem is both channels are really weak and distorted. I can turn the volume pot up by one click, the DDT light kicks in. and the sound is weak. the heatsink gets soo hot to touch, hi temp shutdown kicks in. Both channels are like this.
[......]
Im stuck
If this is like the CS800s I used to fix (is it already 20 years ago? sheesh), you should find a small circuit board on each output binding post. The board will contain some passives and a TO-220 triac; this is a crowbar circuit which keeps a failed output stage from blowing up speakers by shorting the outputs via the triac.
It works well, but you should replace the triac after repairing a blown output stage since the triac also invariably blows while saving the speakers. You can test that by removing the protection board and seeing if the channels start working well again. If that's where the problem lies, I recall the triacs were pretty cheap to replace. Don't have the type number, sorry.
Cheers,
Francois.
no, this unit does not have the triac board.
ok let me explain.
this unit has the screen on the front faceplate, so you can see the last 4 output transistors. it has channel A and B left and right of that screen.
Ive also seen a couple of other versions. the power switch is all the way to the right on this one.
it only has 6 boards. Power board, both input boards, output board, and 2 driver boards. Thats it.
BTW. I replaced those bias diodes once before. but, i didnt know there was a package that has 2 in it. i only used one. i dont think that would do anything would it?
im trying hardly to explain what the sound is like,
its like trying to hook a headphone amp to a big speaker and turning it all the way up.
the sound is very very weak, and realy extremely distorted. only the bass gets through. and the DDT light is solid with or without the defeat swtich turned on.
BTW the triacs are on the output board. There is 2 of them. per channel total of 4. I dont know how to test them, and I pulled them all out of circuit and no difference in sound.
if anyone has the schematic handy, it kept blowing Q16 on the driver board, and the other driver board everything tests perfectly fine.
i was going to flip flop driver boards to indicate that the problem was the driver, or output. I forgot that q16 had shorted again, and hooked that board up to the channel A. thats why channel A has the same problem now as channel b.
ok let me explain.
this unit has the screen on the front faceplate, so you can see the last 4 output transistors. it has channel A and B left and right of that screen.
Ive also seen a couple of other versions. the power switch is all the way to the right on this one.
it only has 6 boards. Power board, both input boards, output board, and 2 driver boards. Thats it.
BTW. I replaced those bias diodes once before. but, i didnt know there was a package that has 2 in it. i only used one. i dont think that would do anything would it?
im trying hardly to explain what the sound is like,
its like trying to hook a headphone amp to a big speaker and turning it all the way up.
the sound is very very weak, and realy extremely distorted. only the bass gets through. and the DDT light is solid with or without the defeat swtich turned on.
BTW the triacs are on the output board. There is 2 of them. per channel total of 4. I dont know how to test them, and I pulled them all out of circuit and no difference in sound.
if anyone has the schematic handy, it kept blowing Q16 on the driver board, and the other driver board everything tests perfectly fine.
i was going to flip flop driver boards to indicate that the problem was the driver, or output. I forgot that q16 had shorted again, and hooked that board up to the channel A. thats why channel A has the same problem now as channel b.
your right there, it would get mighty hot, but it would still sound fine. believe me, ive been there before. I had a bias transistor go on a 60w amp before, and the damn thing would cook eggs wihtin minutes, but it would still sound fine.
Peaveys, are a little bit different. I ran into a CS-400 that the bias network had opened up, and one had shorted blowing one of the output transistors, causing it to swing to the positive rail, which shorted the output transistor, and took out the driver network. and taking the 15amp fuse with it.
after replacing all the bias diodes, and changing both output transistors, along with the driver transistors. The amplifier sang again.
Peaveys, are a little bit different. I ran into a CS-400 that the bias network had opened up, and one had shorted blowing one of the output transistors, causing it to swing to the positive rail, which shorted the output transistor, and took out the driver network. and taking the 15amp fuse with it.
after replacing all the bias diodes, and changing both output transistors, along with the driver transistors. The amplifier sang again.
mbates14 said:
I'll ask you to reconsider. I've *never* seen the triacs blow by themselves - they've always gone after something horrible happened upstream, which has a good chance of happening if the amp is run in yer typical sound reinforcement manner.
I used to keep a few of these things on hand along with spare outputs. I dug knowing I wouldn't have to chew up half my day doing a hundred dollar recone because I could replace in ten minutes a six buck triac that took one for the team.
Cheers,
Francois.
DSP_Geek said:
I have seen these triacs short for no apparent reason several times, and have a mistrust of them for that reason. If I DID own one of these amps (which I don't, I just repair them), then I too would be disconnecting the triacs.
$100 recone vs $100+ in unneccessary amp repairs.......
Still can't beat the old relay disconnect system for DC speaker protection.
Cheers
my experience
I too had the triac go on a CS-800 (old style), but the power amp was fine. I figure it just failed, but I used the amp for another 3 years after with no ill effects.
Also, I just had to comment on these Peavey CS-series amps. I've had several CS' (4 CS-400's, 4 CS-800's and a pair of CS-2000's), and I have found them to be true workhorses and exceptionally reliable and robust. Plus they sound pretty decent and are fairly cheap.
I too had the triac go on a CS-800 (old style), but the power amp was fine. I figure it just failed, but I used the amp for another 3 years after with no ill effects.
Also, I just had to comment on these Peavey CS-series amps. I've had several CS' (4 CS-400's, 4 CS-800's and a pair of CS-2000's), and I have found them to be true workhorses and exceptionally reliable and robust. Plus they sound pretty decent and are fairly cheap.
you want to really know why them triacs blew, its because the dude that owned it before me thought he could repair it, and started to replace resistors with capacitors, and diodes with resistorsm and etc. He didnt understand what they were and how they were different from one another.
and there was also some solder erros in the B channel taht was shorting the VAS feedback circuit to ground.
the one driver board was such bad condition from that mess he did, I had to replace the entire board from peavey for 70+ bux
anyway after correcting all of this, the amp sings again.
and there was also some solder erros in the B channel taht was shorting the VAS feedback circuit to ground.
the one driver board was such bad condition from that mess he did, I had to replace the entire board from peavey for 70+ bux
anyway after correcting all of this, the amp sings again.
What is triggering those triacs in case of DC present on the output?. If they are triggered directly from the output through a simple RC network, the capacitor may be dry or the RC constant may be small enough to allow triggering due to the typical transient signals produced when turning on and off some mixing consoles, equalizers or crossovers when the amp is still turned on
If the trigger thresold is low enough, even the DC introduced by clipping audio signals [asymmetric waveforms] may be enough to activate DC protection
In the other hand, I worked with two old CS-800 [from early 80's I think, about 20 years old now] for the last 4 years and I never saw that DC protection in action. Apparently the only problem these amplifiers had ever shown was the sockets that connect the driver board to the power board and the sockets of the power transistors geting dirty and oxidized and losing contact. I had to 'clean it' once a year or so by sliding the contacts several times
If the trigger thresold is low enough, even the DC introduced by clipping audio signals [asymmetric waveforms] may be enough to activate DC protection
In the other hand, I worked with two old CS-800 [from early 80's I think, about 20 years old now] for the last 4 years and I never saw that DC protection in action. Apparently the only problem these amplifiers had ever shown was the sockets that connect the driver board to the power board and the sockets of the power transistors geting dirty and oxidized and losing contact. I had to 'clean it' once a year or so by sliding the contacts several times
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