KA-907 - No Sound Phono Stage

bce22

Active Member
Happy Thanksgiving my Audiokarma friends,

I have an issue with my KA-907. I turned it on yesterday and I have no sound through the Phono inputs. This morning I opened it up to take a look at the Pre-amp board looking for issues visually. The only visual indication of damage was a burnt resistor (R86 1/4 watt 22ohm). I replaced the resistor and it hasn't popped again but of course this didn't solve the problem.

I can verify that neither Phono 1 or Phono 2 have any output. I also plugged the Turntable into Tape and that doesn't output any sound either. Aux input works fine.

I am hoping that someone can instruct me on how to test this circuit to diagnose the problem. I can read a schematic yet I am not a pro at it yet. I have some test equipment including a Fluke with proper leads and on Friday one of those $25 dollar china meters capable of testing a wide range of capacitance and ESR should arrive. I don't have a scope however.

The service manual for the KA-907 is located on HiFiEngine for those that might be willing to provide some advice. http://www.hifiengine.com/manual_library/kenwood/ka-907.shtml

If anyone would be able to instruct I would really appreciate your help in this matter.

Best Regards,

Brad
 
Did you say that you plugged the phono into the tape and no sound?. Then the phono's output would be wrong... Try a adjustable output source, like
a cd player AT VERY LOW volume, into the KA-907's phono and see it you have sound. Again, make sure you have a very low output on the source
you will use to test the phono input!.
 
Thanks for the things to try. I'll look at the cables first then if that isn't the issue I will try a different source through phono at very low levels to see if I hear any sound.

I'll check in tomorrow evening. Thanks for helping!

Regards,

Brad
 
Go through the Service manual carefully, and make the right adjustments. I believe the Ka-907 has bias adjustment for the Phono stage and/or preamplifier.
 
surely phono plug cable disconnected located at front plate

That's a BINGO! The phono plug cable was disconnected. I have sound in both channels now using phono.

Unfortunately I have a phono problem that is unrelated to my original issue. I noticed last night that at higher volume the amplifier distorts terribly using phono 1 input. It's like a "light switch"; at 11 o'clock it sounds beautiful and at 12 o'clock it distorts. The distortion sounds almost like when a cd starts skipping. It's really strange.

Any ideas on what to check to fix this issue?
 
Is it distorting with phono 2 input?. Do the aux inputs and tape inputs start to distort at 12 oclock?
 
Is it distorting with phono 2 input?. Do the aux inputs and tape inputs start to distort at 12 oclock?

Thanks for helping me turbo!

It happens on phono 2 as well. I'm pretty certain it doesn't happen on aux. I use a laptop through an hrt music streamer II dac. I turned the input volume way down on the laptop and turned the Kenwood volume to 3 o'clock and experienced no distortion at all.

Actually with more thought could the amp be clipping above 12 o'clock on the phono inputs? Does that even make sense? Its really strange that it sounds great then at certain spot on the volume pot it immediately distorts the signal terribly.
 
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Good Evening AK,

Today I checked voltages on the amp. I set power amp bias to 20mv. DC offset at speaker terminals is close to 0mv each channel. I also set the preamp DC offset as well. It was originally about 4V on the right channel :yikes:. I set both channels close to 0mv and they now fluctuate about 5 mv per channel from 0. I also set the DC offset on the tone amp close to 0mv as well.

I am glad I did this however it didn't fix the issue with the distortion of phono above 12 o'clock on the volume dial. Any thoughts on what to test next?

By the way, I have a second donor ka-907 that I can grab unobtainum parts from if necessary, not that I think this particular issue requires it.
 
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