Repairing Kenwood KAC-823 Amp: Unequal + and - Voltage supply
Hi, 1st time poster here. I'm trying to repair a vintage Kenwood KAC-823 power amp.
What it does:
- Turn On (proper led illumination and relay click)
- Voltage step-up works, I get 160 volt AC on output
- Rectifiying diodes do their jobs when center pin is not plugged. reading + 60 Volt DC on one and -60 volts DC on the other
What puzzle me/don't work:
- When I solder the rectifiying diodes back, I get +30 volts DC on one side but -60 volts DC on the other.
- I also don't get any voltage on the negative rail of all the op-amps. It should read -16 volts.
- Test point CN5 does not read 2mv. Actually reads much lower than that. Probably just my multimeter noise I get.
- Test point CN6 reads 30 volts. Should be 31volts. I think it's OK, but not sure.
- Of course it does not output any sound when trying to use it.
I fiddled with electronics for the last 20 years, but it's my second time trying an actual troubleshooting/repair. I would appreciate greatly if someone could point me in the right direction for some more tests.
I found the manual there I hope it's ok with the rules:
https://elektrotanya.com/kenwood_kac-823_sm.pdf/download.html
Edit: My board is X09-3640-10. There are 2 board schematics in the PDF. Mine is the second IIRC.
Thanks guys/gals!
Hi, 1st time poster here. I'm trying to repair a vintage Kenwood KAC-823 power amp.
What it does:
- Turn On (proper led illumination and relay click)
- Voltage step-up works, I get 160 volt AC on output
- Rectifiying diodes do their jobs when center pin is not plugged. reading + 60 Volt DC on one and -60 volts DC on the other
What puzzle me/don't work:
- When I solder the rectifiying diodes back, I get +30 volts DC on one side but -60 volts DC on the other.
- I also don't get any voltage on the negative rail of all the op-amps. It should read -16 volts.
- Test point CN5 does not read 2mv. Actually reads much lower than that. Probably just my multimeter noise I get.
- Test point CN6 reads 30 volts. Should be 31volts. I think it's OK, but not sure.
- Of course it does not output any sound when trying to use it.
I fiddled with electronics for the last 20 years, but it's my second time trying an actual troubleshooting/repair. I would appreciate greatly if someone could point me in the right direction for some more tests.
I found the manual there I hope it's ok with the rules:
https://elektrotanya.com/kenwood_kac-823_sm.pdf/download.html
Edit: My board is X09-3640-10. There are 2 board schematics in the PDF. Mine is the second IIRC.
Thanks guys/gals!
Last edited:
Unfortunately no.
But I figured I could follow the RCA signal input by inputing 60Hz with my phone as a tone generator and using voltmeter on AC.
What were you thinking of verifying with a scope?
Did you check for the open ground?
I wanted you to look at the input to the rectifiers.
Did you find why you had no negative 15v?
I wanted you to look at the input to the rectifiers.
Did you find why you had no negative 15v?
I'm sorry, I'm not sure what open ground means. Is it if the ground is "missing" somewhere (trace cut)? If so, is there a faster way than checking all the ground point one by one? Visually, there's not much happening. No burnt trace or whatnot. But I know that the amp had work done by a more amateur than me. Traces were not conducting, but they were easy to spot beacuse of the poor soldering done. Also, all those missing point were on the signal treatment side, not on the power supply side.
And I'm still searching why no -15 volts. I suspect the unequal +26, -50 volts are related but not found the culprit yet.
Thanks for your interest and ideas to check!
Post the DC voltage on all legs of Q51 and Q52. Place the black probe on one of the negative speaker terminals.
Just found that R76 was dead. It's a resistor between the minus rail voltage and Q52 (transistor?).
Voltage is now +31, -31.
Now on to test with actual sound.
Thanks to those who contributed!!
Forum rocks!
Voltage is now +31, -31.
Now on to test with actual sound.
Thanks to those who contributed!!
Forum rocks!
Well, I now get sound, but a lot of artefact.
If I don't plug any input, and plug the sub bridge with correct adjustement of switch (this amp does not "auto bridge", there is a switch for it) the sub will pop every couple of second.
Also, if plug the sub in non-bridged mode and put actual music, I hear sound, but a lot of noise, like an FM radio not properly tuned.
If I use a tone generator, altought I input a sine wave, it's more like a square wave I hear.
Never encountered this kind of behavior. any idea?
If I don't plug any input, and plug the sub bridge with correct adjustement of switch (this amp does not "auto bridge", there is a switch for it) the sub will pop every couple of second.
Also, if plug the sub in non-bridged mode and put actual music, I hear sound, but a lot of noise, like an FM radio not properly tuned.
If I use a tone generator, altought I input a sine wave, it's more like a square wave I hear.
Never encountered this kind of behavior. any idea?
Compare the voltages in your amp to the ones in the output stage in the diagram. Do they match closely?
Does the 2/4 ohm switch make a difference?
Is your signal source grounded to the 12v supply ground that you're using to power the amp?
Does the 2/4 ohm switch make a difference?
Is your signal source grounded to the 12v supply ground that you're using to power the amp?
No, the signal source is not grounded to the same power supply.
The 2/4 ohm switch does do a appreciable difference.
I'll check the voltage you suggest and report back!
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