KR-4200 A+B speaker output trouble

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by KeithD, Sep 10, 2017.

  1. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Picked up a KR-4200 in nice shape. Had to replace the stereo light, tuner indicator light, and did a general cleaning. Used Deoxit on all switches and pots followed by electronics cleaner. Speakers play well on A and B settings. However, when I switch to A+B, B speakers are fine, but A speakers are super weak. I did go back in and take a close look at that switch and saw black dirt/oxidation on the contacts. Did a combination of mechanical and Deoxit cleaning, but I still have the same issue. Not sure how I am going to get in there to clean better without disassembling the switch, which seems a bit daunting. Any advice? Is this pretty clearly a dirty switch?

    Thanks!
     
  2. sregor

    sregor AK Subscriber Subscriber

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    3,189
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    I don't have a schematic or manual handy, but I believe the A+B position the speakers are in series, so more efficient speakers will seem louder. Quick test is to reverse the A and B speakers, and see if the same speakers seem louder. Since they work by themselves, the only other problem would be the switch, but I find it odd if it is both channels, as they are separate connections. Good luck.
     
  3. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    After some more tests, it looks like the cleaning took care of the problem. Seems to be working fine on both speakers. Thanks!
     
  4. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    OK, I now realize what the problem is. I have a Niles SVC-1 volume control between the receiver and the B speakers in order to set the B speakers at a lower volume than the A speakers for my setup. However, when I turn down the volume on the B speakers the A speakers also drop in volume. I don't really quite understand this, but is there a way to reduce the volume of the B speakers independent of the A speakers?
     
  5. sregor

    sregor AK Subscriber Subscriber

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    3,189
    Location:
    Mass
    Goes back to the speaker connections in series mentioned previously. In the A+B position, the signal goes from one (A? have to look at schematic) to the positive, then the negative (black?) to the second speakers positive (red?) and the second speakers negative is ground.
    You would have to figure out a way to rewire the speaker switch - requiring research, thought, and circuit modification. Or find a cheap speaker switch and connect it to the A speakers, and leave the amp in A speakers only mode. Lower range receivers did this to prevent loads going below 8 ohms when A+B is selected.
     
  6. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    OK, thanks. I actually did try the first solution this morning. I had a 6-way speaker switch sitting around and connected the input to speaker A on the receiver. That worked.

    However, I've discovered a different issue. There is a low background hum in the speaker outputs/headphone output. From what I've read, this may be a transistor issue in the signal path. Are there transistors that are known to go bad or cause this type of problem in the 4200? Or is this a capacitor issue?
     
  7. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    1,197
    Location:
    Victoria, Australia
    If the hum is in both channels it will either be a bad cap in the power supply or a bad ground. I had a KR-5200 about 6 months ago that had a low level hum in both channels and l ended up having to add a wire between the pre amp ground and the main ground point over near the main filter caps l think. All of the factory ground wires were in place and tested perfectly with hum present.
     
  8. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Actually, after listening to the background noise, it seem like more of a hiss than hum sound that you get with grounding issues. Also the hiss increases as I increase the volume. I've noticed the same thing on my KR 3200 in testing with the same speakers. So, now I'm wondering if it is normal or a sign of something wrong in both receivers?
     
  9. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    1,197
    Location:
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    Yes if it is a hiss rather than a hum it much more likely to be caused by transistors. Is it the same in both channels? Are the speakers you are using super efficient?
     
  10. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    A further update: being more systematic with my testing on both the 3200 and 4200, I think things are ok. I was hearing static, which depended on the volume control when each unit was set to phono with no phono connected. When I switch to AUX with nothing connected to that input there is little to no static even at the highest volume setting. This is probably normal, right? I'll check the phono inputs with a turntable connected next to see if that minimizes the hiss on the phono setting.
     
  11. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

    Messages:
    1,197
    Location:
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    Yes it is normal to get much higher hiss on the phono input than aux/tape etc with nothing connected due to the much higher gain in the EQ (phono) amp.
     
  12. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Ok, then I think everything is working with these great little units. I was given the KR 3200 free, but it did not have its cover. I purchased the 4200 locally. The 3200 did not sound great, but I had not done anything too it. After using deoxit on all the switches and pots, and oiling the pulleys for the tuner string I was amazed at the sound difference and great quality. The tuner knob also moves really smooth and the tuner pulls in stations well. Made a cover for it out of solid red oak with a walnut stain. Looks better than what it came with, in my opinion.

    I was so impressed by the 3200 after cleaning it up that I bought the 4200 I came across for sale locally. That one had the stereo and dial indicator lights burned out, but I had spares of the correct "grain" bulbs from another project. So I replaced those and did the same cleaning. Again sounds wonderful, tuner moves smoothly. To me, they sound just as good as my higher end Pioneer gear. I think these are really undervalued. Especially the 4200 with two tape inputs and two AUX inputs, they are pretty versatile. Main complaint there is the A and B speaker outputs are not independent.
     
  13. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

    Messages:
    1,197
    Location:
    Victoria, Australia
    That sounds really nice, do you have any photos?

    You are spot on, l really like this series also, they sound great and are built very well, completely undervalued, l agree 100%
     
  14. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Here they are. I made the sides out of the same piece of wood and oriented them as a "book match" so that the rays of the grain point outward in a mirror image. The case was made from 3/4 inch oak, which is what I had on hand. I think the original cases are 1/2 or 3/8 inch, so this looks a little "bulky" in comparison, but I do like the color and wood grain.
    KR3200 front.jpeg KR3200 left end.jpeg KR3200 right.jpeg KR3200 top.jpeg
     
  15. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

    Messages:
    1,197
    Location:
    Victoria, Australia
    Great job on that case, l like the walnut :thumbsup:.
     
  16. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Thanks! Do you happen to have or know where I can download the manuals for the 4200? I have the service manual for the 3200, but Hifiengine does not have any manuals for the 4200.

    Also, what's the deal with the higher models in this series having the Tape B inputs on the front as headphone jacks? That seems really strange to me and a big drawback to those models.
     
  17. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

    Messages:
    1,197
    Location:
    Victoria, Australia
    Sorry, no l don't know of a reputable source for the service manual, if you need to set the BIAS, there is a really good document released from Kenwood years ago. Just google Kenwood bias setting and half way down the first page there will be a link from vintagehifi.com called ''Kenwood Audio Adjustment''.

    I am not sure why Kenwood used 6.5mm jacks for the tape 2 input on the 5200, 6200 and the 7200.
     
    Last edited: Sep 17, 2017
  18. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    So, here's an update on the 4200. It's become apparent that the issue is with the right channel speaker output. There is a constant background hiss or static only on the right speaker output, left is pretty silent. Also, the static is independent of the volume knob - just a constant level no matter the input or volume. Anyone have insight on what this might be, or where I should look to troubleshoot?

    Thanks!
     

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