Hi,
I have a Kenwood KAC 9104d which remains in protection when powered up.
Given my recent adventures in DIY audio I should like to have a crack at repairing it.
I opened it up and didn’t find any obviously burned or exploded parts. The caps, 105 degree Elna(!), seems fine too.
I tried to power it up with a stabalised power supply, turning the voltage up first. It got to 8 volts and the blue light on the front turned on. Trying to adjust the voltage higher wouldn’t work and checking the current mode of the power supply showed that it was limiting the draw to 0.4amps. This was preventing the voltage from climbing any higher and so easing off on the current limiter got amp on and showing the red protection light at 10.5 volts, at which point it was drawing a full amp.
I have the service manual and would love to try and repair this amp as a learning excercise.
Following Mr. Babin’s guide I determined that there was + -50 volts at the output transistors and at the two power diodes but couldn’t take the pan chip voltages as they are on the other side of the board.
I am loathe to break the union between the heatsinks and the transistors until I have done all the testing I can from the side of the board that is visible, what other diagnostic checks can I make before I turn the board over?
Here is a copy of the service manual and the schematic : https://elektrotanya.com/cgi-bin/download2.cgi?fid=192949&file=kenwood_kac-9104d_sm.pdf
I have a Kenwood KAC 9104d which remains in protection when powered up.
Given my recent adventures in DIY audio I should like to have a crack at repairing it.
I opened it up and didn’t find any obviously burned or exploded parts. The caps, 105 degree Elna(!), seems fine too.
I tried to power it up with a stabalised power supply, turning the voltage up first. It got to 8 volts and the blue light on the front turned on. Trying to adjust the voltage higher wouldn’t work and checking the current mode of the power supply showed that it was limiting the draw to 0.4amps. This was preventing the voltage from climbing any higher and so easing off on the current limiter got amp on and showing the red protection light at 10.5 volts, at which point it was drawing a full amp.
I have the service manual and would love to try and repair this amp as a learning excercise.
Following Mr. Babin’s guide I determined that there was + -50 volts at the output transistors and at the two power diodes but couldn’t take the pan chip voltages as they are on the other side of the board.
I am loathe to break the union between the heatsinks and the transistors until I have done all the testing I can from the side of the board that is visible, what other diagnostic checks can I make before I turn the board over?
Here is a copy of the service manual and the schematic : https://elektrotanya.com/cgi-bin/download2.cgi?fid=192949&file=kenwood_kac-9104d_sm.pdf
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Given that I performed the automotive equivalent of a dim bulb test ( possibly unintentional pun at my own expense there... 😀), there is a pretty serious short somewhere.
If I have understood my basic reading correctly then the indiaction of +- rail voltages indicates that the DC-DC power supply is probably ok.
The fact that I can measure rail voltage at the legs of the output transistors might mean that they are shorted?
I will make some time to take it out of the heatsink and measure the voltages on the pins of the 494 IC today, thank you for your help. 🙂
I haven’t connected it to a high current capable supply yet but will do so right now.
Edit. Nope no fuses blown, protection light on. There is high pitched squeal coming from the area of q702/q701 though. The squeal starts up after a few seconds and varies in pitch slightly, warbling almost, and then stops after a few more seconds
Edit. Nope no fuses blown, protection light on. There is high pitched squeal coming from the area of q702/q701 though. The squeal starts up after a few seconds and varies in pitch slightly, warbling almost, and then stops after a few more seconds
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The power Led is blue (two of them in fact) and is on as normal.
The status Led is single and remains red. I gather it ought to be green.
The whining noise is permanent and sounds like it is at around8khz plus. It is constant now with the power on.
The status Led is single and remains red. I gather it ought to be green.
The whining noise is permanent and sounds like it is at around8khz plus. It is constant now with the power on.
I confess I have not, the amp was sold as not producing any sound and I took the seller at their word that it didn't work...
Have I just made an enormous fool of my self?😱
I'll try a source and speakers just now...
Have I just made an enormous fool of my self?😱
I'll try a source and speakers just now...
F*&$$ing C*^%ing thing seems to work...😱
At 200 hz at least...
Erm... 😱
I shall have to test it properly to make sure it doesn't cut out under power. Is that high current draw normal?
At 200 hz at least...
Erm... 😱
I shall have to test it properly to make sure it doesn't cut out under power. Is that high current draw normal?
What high current draw. I think I saw 1 amp in one post. Is it drawing significantly more than that?
If you power it up and let it idle for 10 minutes, does it get hot?
If you power it up and let it idle for 10 minutes, does it get hot?
Yes the 1 amp, I thought it was high as the other class D amp I have draws something like 100ma without signal.
The amp has been on for ten minutes now, only the central transformer ( between the two inductors) is a little warm.
100hz test tone, 3,150mv RMS speaker out puts.
Q110 and Q110 also get warm but not too hot to touch.
The amp has been on for ten minutes now, only the central transformer ( between the two inductors) is a little warm.
100hz test tone, 3,150mv RMS speaker out puts.
Q110 and Q110 also get warm but not too hot to touch.
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1 amp is insignificant. Many class D amps draw more than 2 amps at idle.
Many times, when an amp won't produce audio, it's simply a dirty switch or potentiometer or a switch that's between the contacts (wasn't pushed far enough).
Many times, when an amp won't produce audio, it's simply a dirty switch or potentiometer or a switch that's between the contacts (wasn't pushed far enough).
That’s marvellous, thank you. I shall have to put it in the car and give it a proper test to see if holds up under load but I think it’s safe to say that the first lesson in car amplifier repair is “is it actually broken”... 😀
Thanks again for your patience, very kind of you to take the time to help a plonker like me! 🙂
Thanks again for your patience, very kind of you to take the time to help a plonker like me! 🙂
Update.
Having tested it for a few days it seems to work perfectly.
I'm back on ebay looking for a non-working amplifier to play with.😀
Once again thank you for the help.
Having tested it for a few days it seems to work perfectly.
I'm back on ebay looking for a non-working amplifier to play with.😀
Once again thank you for the help.
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