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KA-9100 Switch Pop

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by tinkerer, Jul 4, 2018.

  1. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    Happy 4th of July. God Bless America.

    I have a Kenwood KA-9100 Int Amp I'm getting back up to speed and have an issue I'm trying to run down.

    Issue: Pop in Loudness Switch when moved back to center from either up or down. No pop when moving the opposite (from center to up or down) The Right Power Meter jumps up at the same time.

    Same issue with the Monitor Switch when switched to either Monitor 1 or 2. Pop in right channel and right power meter jumps.

    When Volume Control is turned counterclockwise to No Volume the right power meter jumps right at the end.

    This only happens when there is input from any source. No input...No Pop

    Controls have been cleaned at least twice.

    Tested as PreAmp Only, and the issue is present in PreAmp.

    When Mode is set to Reverse the issue moves to Left Channel.

    When Mode is set to Mono the issue is present in both channels.

    The Power Supply board has been recapped. No other work has been done.

    Looking at the Block and Level Diagram I suspect either the Flat Amp or Tone Amp

    Any suggestions would be greatly appreciated.
    Thanks........Jim
     

     

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  2. inductor

    inductor Super Member

    Messages:
    1,572
    Location:
    uk
    probably a leaky tantalum or similar capacitor, or mucky switches
     
  3. lha1992

    lha1992 Kenwood Collector Subscriber

    Messages:
    5,542
    Location:
    Everett, WA
    Double check and deoxit those switches again. They can be tricky and tight on the 9100 to clean and get to. Just try to work as much as you can in and follow with faderlube afterwards.

    The low and high filter push button switches can be a culprit on this old amp. Try if you can to get some deoxit into them. It's rough and I do remember that Kenwood issued a service fix for people who experienced a drop of a channel to do some bypass of the switch. I'l have to look back and find out.
     
  4. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    Could be the switches......but it's curious that everything is happening in the right channel.
    I'll redo the deoxit and see if that helps.
    Not dropping a channel Iha1992.
     
  5. lha1992

    lha1992 Kenwood Collector Subscriber

    Messages:
    5,542
    Location:
    Everett, WA
    Definitely redo the deoxit on the switches. And I knew you weren't experiencing a channel drop out but thought id throw that out there.
    Kenwood back then knew they had an issue with the low and high filter push button switches. Honestly, thinking back about my KA-9100, I had an issue like yours but I cant remember what my fix was for it haha. I fixed it like 8yrs ago and been out of the HI-FI game for almost 4yrs til just
    recently.
     
  6. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    I've redone the deoxit D5 on all the switches. Still got the same issues, plus distortion in left channel. I've sprayed the switches every which way I can think of, every opening, up, down, sideways. I've desoldered the Volume/Balance rotary pots (again) and flushed it multiple times while rotating. If anything all the cleaning made matters worse, certainly no better. So I'm back to square one. Still can't swear it's not in a switch or multiple switches. Everything seems to be happening before the flat amp or possibly in the flat amp. I'm gonna see if I can trace the sound thru the switches to maybe narrow down where the problem is. Not feeling a lot of love from this amp right now, it's fighting me pretty hard. :(
     

     

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  7. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    559
    Location:
    San Diego, CA
    Some switch contacts can be gunked up to the point that spraying doesn't fix'em. You may have to take them apart and clean the contacts. Somewhere in the KW forum is a post or two regarding doing just that. It's not difficult, you just have to be patient and make sure you put them back together the way they came apart.
     
  8. Chip Chester

    Chip Chester Super Member

    Messages:
    1,970
    Location:
    Central Ohio
    Since you have one working channel and one popper, troubleshooting will be easier. Grab your oscilloscope, and start checking for a DC offset present on the right channel that's not present on the left channel. Start at the switch, and first start at the 'output' side of any coupling caps (that have the audio signal going through them). I'm guessing you'll find a DC component on your right signal that's not there on the left when looking at that channel's cap. If you have a schematic, it may help to post it. If you're not comfortable with (or don't have) an oscilloscope, then a systematic re-cap of the audio chain would probably fix the problem -- but it won't catch issues caused by other components.
     
  9. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,094
    Location:
    Vancouver, WA
  10. 50nstillhifi

    50nstillhifi Super Member

    Messages:
    1,076
    Location:
    Carolinas
    The 9100 dilemma strikes again!

    Yes, this is a recurring issue with this Kenny, and will lead you to believe all sorts of circuitry is failing you. Take the advice of the prior posters and do a deliberate and intense "deoxit" of the switches. Deoxit may not solve the issue but diminish it.

    Got more time :idea:, suggest the following:

    • Panel removal (front face).
    • Good and pointed vacuuming of each switch.
    • A good solvent applied to the actual switch mechanism (I used WD40, a "solvent").
    • A re-lube after again vacuuming of the switch and its housing. (I used teflon oil, a "lubricant").

    Now here is the down side.. this takes lots of time, as the process may need to be repeated.

    I enjoy my Kenwood 9100, but not enough to go in and out of its innards to keep it functional :no:

    Eventually I repositioned it as the "work horse" of my home rack system.
     
  11. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    Thanks everyone for the help.

    I agree that until I can be certain that ALL the switches are cleaned and functioning properly I'm chasing my tail.
    Removing and taking all the switches apart is a major undertaking. I have taken switches apart before so I believe I can manage it.
    It's devoting a solid week to the project that is going to be difficult.
    I'll have to give it some thought.
    Maybe worth the effort being the KA-9100 Amp, KT-8300 Tuner, and Rare Double Wood Case. Can't get a pic to upload for some reason
    I'll report back.
    Thanks again.
     

     

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  12. 50nstillhifi

    50nstillhifi Super Member

    Messages:
    1,076
    Location:
    Carolinas
    Well thought out..! :thumbsup:
     
  13. SicMan

    SicMan Fire up those speakers Subscriber

    Messages:
    2,973
    Location:
    Wolcott - CT. USA
    Could be the offset in the right channel is out of spec a ways. And don't forget the signal goes thru all the switches.

    7/11/2018 --> possible broken ground wire.

    my .02

    John
     
    Last edited: Jul 11, 2018
  14. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    Center Voltage (Bias) is the only adjustment according to the SM, and both R & L are somewhat stable at 0V + or - 5mV.

    Will look again for broken ground wires.

    I removed the Loudness switch and disassembled, cleaned, and reinstalled. Pop still there.
    It was somewhat tarnished but I didn't see anything that looked bad enough to be causing an issue.
    I'm going to leave the other switches alone for now since the loudness switch appeared functional.

    I'm going to rebuild the tone board.
    I was hoping to use this amp with just a cleaning, but here I am several weeks in with something still amiss. Welcome again to vintage 40 year old equipment. :whip:
     
  15. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,094
    Location:
    Vancouver, WA
    FYI - "Center Voltage" is DC offset. 0 is good! Bias is non adjustable on these.

    Don't forget to clean the normal/separate switch on the rear panel, always a concern on these
     
  16. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    10-4

    Normal/Separate switch cleaned when power supply was recapped.
     

     

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  17. SicMan

    SicMan Fire up those speakers Subscriber

    Messages:
    2,973
    Location:
    Wolcott - CT. USA
    Just for giggles see if the relay is getting interrupted when the problem happens.

    It's supposed to when you change the speaker select switch. It turns the relay off when switching from A to B etc. and back on quickly. I've had a couple bad contacts in one that did that very loud in one channel and another in both channels.

    John
     
  18. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    The relay isn't acting up when the pop occurs. The relay does turn on/off when switching speakers. I have thought of cleaning the contacts on the relay but haven't.
     
  19. tinkerer

    tinkerer AK Subscriber Subscriber

    Messages:
    232
    Location:
    Bowling Green, KY
    So I've recapped the tone boards X11-1410-00-A/4 and X11-1410-00-D/4. I did not change any transistors.
    Seems all I accomplished was to create more problems. I'll have to take all that mess apart again and see if I got a cap in backwards.
    Pop still there. The treble control doesn't seem to make any difference in sound. Bass works as it should.
    High filter push switch now makes a pop (wasn't there before) and the left power meter shows an increase from 0 output to 3 watts without any input or volume.
    Like I said I'll have to go back in and check my work. This time I'll go ahead and change out transistors except for the 2SK68A's.
    Not having much fun working on this one. My troubleshooting skills are not the best.
     
  20. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    559
    Location:
    San Diego, CA

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