Is that 6 volts DC? if so the diac-triac protection circuit should have shorted the output to speaker return. Is the triac land burned off the output transistor PCB like in my PV1.3K? Then there is no protection. I test the diac with 9 VDC with a 470 ohm resistor in series, to make sure it breaks over. One was bad. My triacs were totally shorted, didn't need a special test jig for them.
The double diode test on output transistors with a DVmeter can prove them bad, but not prove them good. Next time I'm going to bias them to 19 VDC (out of an old car battery charger) c-e with the base open (opposite polarity for PNP) and measure the leakage current to see if I can detect the bad output transistors. After a previous owner O.T. meltdown, I removed and checked all the O.T.'s with a meter. Many emmiter resistors were bad, too. I put 7 old O.T.'s back in the unit because they passed the meter check, and 2 more O.T.'s blew up immediately on power up.
The double diode test on output transistors with a DVmeter can prove them bad, but not prove them good. Next time I'm going to bias them to 19 VDC (out of an old car battery charger) c-e with the base open (opposite polarity for PNP) and measure the leakage current to see if I can detect the bad output transistors. After a previous owner O.T. meltdown, I removed and checked all the O.T.'s with a meter. Many emmiter resistors were bad, too. I put 7 old O.T.'s back in the unit because they passed the meter check, and 2 more O.T.'s blew up immediately on power up.
dry joints on the driver pcb's check for loose/cracked pcbs..you can remove the triac for testing these heavy old amp out..I've serviced many of these plus the 1k3 pv's...in the end i build a relay protection pcb for both amps that trigger if there was dc at the speaker end saves many a speaker!
Look for outputs on the driver pcb to the O.T. bases drifting off zero when this occurs. Ground the meter minus to speaker return using a clip lead. If the base drive is getting off zero, trace it back through the circuit to the source. If you recently replaced O.T.'s, you might find the feedback resistors to the driver PCB are burnt out too. Many of mine were.
As the driver pcbs are stacked on my 1.3K, I had to build a contraption using a stand to hold the master pcb in the air while I probed around on the slave channel pcb . On my amp the DC voltages from Power Supply only went to one PCb, then were relayed to the other by an interboard cable. Be glad the problem is only DC, if you had motorboating like I do, you have to probe with a scope or fast AC meter. DVM's are too slow to catch this, I'm using a simpson 260 vom on AC scale with a 1 uf capacitor in series with the plus probe, since the AC scale reads on DC, too. My scope sweep just quit, I'd like to finish the amp and get it off the coffee table before diving into the power supply of the scope.
Anatech, glad to hear somebody else thought of using the diac to trigger a disconnect relay. I am putting something together to do this, but wasn't sure it would be fast enough to save a speaker. I'm using a 120 VAC coil 460V contactor which is supposed to be an especially fast relay, since they trade speed of contact hit for the smaller size of the contact compared to the old standard contactors. (1/4 size).
As the driver pcbs are stacked on my 1.3K, I had to build a contraption using a stand to hold the master pcb in the air while I probed around on the slave channel pcb . On my amp the DC voltages from Power Supply only went to one PCb, then were relayed to the other by an interboard cable. Be glad the problem is only DC, if you had motorboating like I do, you have to probe with a scope or fast AC meter. DVM's are too slow to catch this, I'm using a simpson 260 vom on AC scale with a 1 uf capacitor in series with the plus probe, since the AC scale reads on DC, too. My scope sweep just quit, I'd like to finish the amp and get it off the coffee table before diving into the power supply of the scope.
Anatech, glad to hear somebody else thought of using the diac to trigger a disconnect relay. I am putting something together to do this, but wasn't sure it would be fast enough to save a speaker. I'm using a 120 VAC coil 460V contactor which is supposed to be an especially fast relay, since they trade speed of contact hit for the smaller size of the contact compared to the old standard contactors. (1/4 size).
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The CS800 is not laid out like the PV1.3k.
Isolate the problem.
Are you telling us BOTH channels get 6vDC offset? Or just one of them?
Make sure the switch is set for STEREO. At least during testing.
If both channels do this, make sure both main power supply voltages are equal. Easy to check at the two large fitler cap terminals. Then make sure the 15v supplies for the op amps are BOTH up to voltage.
There is enough extra wire that you can dismount the two power modules and set them off to each side. Put something between the modlue and the side of the amp so nothing shorts to chassis when you do this.
That will get you access to the bottom of the chassis wher the 15v zeners are, at least on the C version. In any case, you can also get access to the op amps that way, so check right at their power supply pins.
If power suply is OK, then we dig further. If only one channel is bad and the other good, mark the boards from the bad side, then exchange the driver card (from the underside of the power module) with the one on the other module. If the problem remains the same, then the driver card is not the problem. But if the problem moves to the other channel, then the driver card has the fault.
DO you know which version your amp is? CS800 A series has only one op amp IC on the driver card, and on the little board for the volume control, there is only the control, one resistor, and two small transistors.
The CS800 C series (also called the zener version) has two ICs on the driver card, and the volume control board has also two ICs on it.
And does teh volume control have a pull switch?
Isolate the problem.
Are you telling us BOTH channels get 6vDC offset? Or just one of them?
Make sure the switch is set for STEREO. At least during testing.
If both channels do this, make sure both main power supply voltages are equal. Easy to check at the two large fitler cap terminals. Then make sure the 15v supplies for the op amps are BOTH up to voltage.
There is enough extra wire that you can dismount the two power modules and set them off to each side. Put something between the modlue and the side of the amp so nothing shorts to chassis when you do this.
That will get you access to the bottom of the chassis wher the 15v zeners are, at least on the C version. In any case, you can also get access to the op amps that way, so check right at their power supply pins.
If power suply is OK, then we dig further. If only one channel is bad and the other good, mark the boards from the bad side, then exchange the driver card (from the underside of the power module) with the one on the other module. If the problem remains the same, then the driver card is not the problem. But if the problem moves to the other channel, then the driver card has the fault.
DO you know which version your amp is? CS800 A series has only one op amp IC on the driver card, and on the little board for the volume control, there is only the control, one resistor, and two small transistors.
The CS800 C series (also called the zener version) has two ICs on the driver card, and the volume control board has also two ICs on it.
And does teh volume control have a pull switch?
got 1 channel playing
when there is no speaker connected there is no 6 volts on turn on but if u connect a speaker after it plays beautiful is it the triac causing it ? but other wise it works fine and it is the cs800s
found some dry joints on the driver board solder them up but same thing as long as there is no speaker at turn on the amps will play if u connect a speaker later while the amps is on hope that made it more easier for u guys to help
when there is no speaker connected there is no 6 volts on turn on but if u connect a speaker after it plays beautiful is it the triac causing it ? but other wise it works fine and it is the cs800s
found some dry joints on the driver board solder them up but same thing as long as there is no speaker at turn on the amps will play if u connect a speaker later while the amps is on hope that made it more easier for u guys to help
Goldfingerxus, these amps gave a audible thumb at switch on off in to the speaker load..it's not a good idea to power up then hook the speaker load. As enzo says these are easy to work on and if need be you can remove one channel at a time to sort the fault.. this 6 volts your reading what channel is it on? oh watch out for them 15000uf 90 caps they can hold there change for days...just discharge them with a standard 60w bulb..also you can solder 4k7 at 5 watt across each one these bleeder resistor's will drain them when the amp is not in use.
@ indianajo, if your going to add a speaker relay system remove the triac altogether as the only thing these did was to activate if there was 20vdc or more volts at the o/p and short the whole out put stage to ground blowing the main fuse plus taking many of the power transistors with it.. most protection speaker relay circuits would trip the relay off if the o/p was say 1 volt dc or more saving speakers from being burnt! you can get circuit information on the net to build a unit or buy one.. they included soft start to remove the pop..wait led and ready led. plus power off so to remove that pop at power off. use this type of relay...12vdc coil with 10amp or more contact rating's.
@ indianajo, if your going to add a speaker relay system remove the triac altogether as the only thing these did was to activate if there was 20vdc or more volts at the o/p and short the whole out put stage to ground blowing the main fuse plus taking many of the power transistors with it.. most protection speaker relay circuits would trip the relay off if the o/p was say 1 volt dc or more saving speakers from being burnt! you can get circuit information on the net to build a unit or buy one.. they included soft start to remove the pop..wait led and ready led. plus power off so to remove that pop at power off. use this type of relay...12vdc coil with 10amp or more contact rating's.
Look for ultrasonic oscillation when the speaker is connected. That can do weird things - including throw off the DC bias and offset. 2nd harmonic distortion in the oscillation tone will do this. Does it do this with a pure resistor load? I'm guessing not. A different speaker (or cable) may also behave differently.
how true... connector issues are the root cause in so many weird problems. I remember my friend's 1990 Dodge colt had an interseting issue in that his dashboard lights were dimming and the gauges were going nuts... He'd trun on the headlights and the turn signals would start flasing or something like that... Turned yout it was a ground connection that failed in the electrical system.
Regarding your signature Mr Hoffman, euh, what exactly does it mean? I find it funny but I don't quite get it! lol (Don't worry I'm not offended as I am not an audiofool or file...)
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