Thank you for the better schematic! It's enormously helpful.
If I'm guessing correctly, R9 and R10 (page 2 of your schematic) are the volume controls? Please confirm.
Is the volume the +10V mentioned seen at pin 3 of R9 and pin 1 of R10? If so, this is very likely the root problem--- the voltage across these pot elements should be ~0V. Can you discover how +10V finds its way into the controls?
I can't sort out the cable connections of the volume pots into the amp. Would you clarify for me? Eg. J7 and J8 go from volume controls to where?
Thanks.
If I'm guessing correctly, R9 and R10 (page 2 of your schematic) are the volume controls? Please confirm.
Is the volume the +10V mentioned seen at pin 3 of R9 and pin 1 of R10? If so, this is very likely the root problem--- the voltage across these pot elements should be ~0V. Can you discover how +10V finds its way into the controls?
I can't sort out the cable connections of the volume pots into the amp. Would you clarify for me? Eg. J7 and J8 go from volume controls to where?
Thanks.
Looks to me as if thats them on the Schematic. The Volume cables ,send & return to J5 & J6 on the actual board.
The red wires have 10v on them. The black wires are the ones that go up in voltage as you turn up the volume.
The red wires have 10v on them. The black wires are the ones that go up in voltage as you turn up the volume.
I can't reconcile the picture with the schematic. If there's good correlation, can you help me understand?
Perhaps the schematic is not correct for your amp? Maybe there's a better match, even if less clear. In any case, I suspect a defect that delivers +10V to the top of the pot. Try probing with you meter to find the source of 10V. Look for solder shorts, defective caps, etc. What is output voltage on nearby opamps?
Good luck!
Perhaps the schematic is not correct for your amp? Maybe there's a better match, even if less clear. In any case, I suspect a defect that delivers +10V to the top of the pot. Try probing with you meter to find the source of 10V. Look for solder shorts, defective caps, etc. What is output voltage on nearby opamps?
Good luck!
The L&R signals leave IC1B IC2B and return to IC1A and IC2A on Page 5 of the Schematic.
On mine theres only IC1.
Caps 122 and 222 have 10v on them at one end and 3v on the other.
The IC is getting 20v + and -.
On mine theres only IC1.
Caps 122 and 222 have 10v on them at one end and 3v on the other.
The IC is getting 20v + and -.
I've got 10v+ Pin 1 and 10v+ on Pin 7 of IC1. Its the same as the Volume just below 10v. Same as those caps.
I've got 20v+ on Pin 8 aswell on....... IC1. I've got 0v on Pin 4.
I've got 20v+ on Pin 8 aswell on....... IC1. I've got 0v on Pin 4.
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I have to leave for errands, by try to find the path that generates +10V. Also report all voltages appearing on pins of IC1 for possible insights. For example if pin 2 and 3 have equal voltages, that suggests pin 1 voltage may be in active/linear state. Similar for pins 4 & 5 re state of pin 7.
Is IC1 hot?
Also see if you find a more accurate schematic.
Is IC1 hot?
Also see if you find a more accurate schematic.
Thanks for the help so far man. we're getting closer I think. I'm wondering if somehow 20v is being split in two.
10v is on both left and right. But no 20v.
IC4 has fair bit going on aswell. on the Schematic.
Yea the schematic is a pain ,I said that in the beginning.
I'll get all the pins voltages and type them in.
10v is on both left and right. But no 20v.
IC4 has fair bit going on aswell. on the Schematic.
Yea the schematic is a pain ,I said that in the beginning.
I'll get all the pins voltages and type them in.
Theres two 3.9K 5 watt Resistors on the Power Supply. + and -.
+85v to +20v on the + one.
-85v to 0v on the - one.
+85v to +20v on the + one.
-85v to 0v on the - one.
Well, things look completely mysterious. Without a schematic, we're reduced to near guesswork. I'll pose a mix of observations, guesses, and attendant questions.
Are your posted pictures of your amp? I infer that your IC1 is OP725 rather than OPA2604 as implied in the schematic. Do you see any evidence that the existing OP725 is a replacement? There's a lot of circumstantial evidence for suspicion:
The opamp appears to be misbehaving. With the + inputs at a voltage lower than the - inputs, the opamp outputs should stick on the negative rail, but they are positive. No clue why they would present +10V other than part failure.
Your measurement shows +0.7V on IC1 pin 4--- very odd. Schematic (valid?) indicates -22V is expected. +/-22V powering an OP725 is well above its rated voltage, but well within OPA2604 specs. You mentioned finding "two 3.9K 5 watt Resistors on the Power Supply. + and -." Measure the voltage on the 3.9k resistor powering the negative supply. Is it +0.7V ?
These musings/speculations are building a case to perhaps replace the IC1 site with an IC socket, then try a OPA2604 replacement.
Are your posted pictures of your amp? I infer that your IC1 is OP725 rather than OPA2604 as implied in the schematic. Do you see any evidence that the existing OP725 is a replacement? There's a lot of circumstantial evidence for suspicion:
The opamp appears to be misbehaving. With the + inputs at a voltage lower than the - inputs, the opamp outputs should stick on the negative rail, but they are positive. No clue why they would present +10V other than part failure.
Your measurement shows +0.7V on IC1 pin 4--- very odd. Schematic (valid?) indicates -22V is expected. +/-22V powering an OP725 is well above its rated voltage, but well within OPA2604 specs. You mentioned finding "two 3.9K 5 watt Resistors on the Power Supply. + and -." Measure the voltage on the 3.9k resistor powering the negative supply. Is it +0.7V ?
These musings/speculations are building a case to perhaps replace the IC1 site with an IC socket, then try a OPA2604 replacement.
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Still, I think the differential voltage between + and - inputs should force the opamp to the negative rail. I infer that supply voltage is currently within allowed range, yet malfunctioning. Leading me to guess that supply voltage abuse led to destruction.
Big guesses with scant real data. 😆
Big guesses with scant real data. 😆
Hi again.
Yeah ,they're pictures are of my Amp. I took them myself with the help of a lamp.
I've got another one of these Amps to compare it to. I recapped that one aswell. I've not really tested it yet as I wanted to recap them both first. I thought I'd test this one first as it had evidence of a major accident. I had to replace the Big caps. Just in case. I think that below took out that resistor. I've got more photos of that aswell. The board,the cap.
I was thinking that if the -22 isn't there ,there's nothing to counter the positive to bring it to 0v. I think that 3.9k resistor is open. Maybe try a similar scenario on a breadboard and see.
I've got some new resistors on the way. I could bring that voltage down with a different value on them. We haven't got the board info so don't know what else is using the 22v. Or try a similar IC with a higher voltage rating.
The measurement on the - Resistor is 0v.
There is sound from the amp on both channels and it sounds good for how far I can turn the volumes up.
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I followed the track from the 3.9k Resistor and it goes to a diode which I guess is connected to GND on one side. Then goes to a cap then onto no4 pin on IC1. I'll have another look later on see if anything else is there.
BTW. The CA18 uses the OP275 aswell.
BTW. The CA18 uses the OP275 aswell.
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But apparently, +/-20v not +/-22. I know, it gives headroom in the front end section to run op amps up there, allowing a hotter signal which is then attenuated by the gain controls (and IGM soft clipping circuit). But in this level of professional equipment, running op amps above +/-15V is really a bad idea. These amps in general get high marks for durability, but not reliability. I’ve never seen a failure in the power section (from driving heavy loads for too long), but in all the poorly engineered cr@p around them.
wg_ski
Do you reckon it would be worth doing that.? I'll replace the resistors and see. I could raise them a bit.
Yea. Its always 15v on the opamps ,sometimes 18v.
What do you think about using non cement type.? Would it matter much in that position.?
I've asked Peavey if they got a CA4 Specific Schematic.
Do you reckon it would be worth doing that.? I'll replace the resistors and see. I could raise them a bit.
Yea. Its always 15v on the opamps ,sometimes 18v.
What do you think about using non cement type.? Would it matter much in that position.?
I've asked Peavey if they got a CA4 Specific Schematic.