Kenwood ka-9100 help

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by rossm, Feb 17, 2018.

  1. rossm

    rossm AK Subscriber Subscriber

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    Hi
    Any experts on the KA-9100 amps ? I hoping to restore a kenwood ka-9100.
    The schematic shows 26.8v dc on the output (pin 5) of the power amp IC (pin 7 on the card), this looks to be the output to the speaker. What am I missing here ? that can't be right having 26.8v dc voltage sent to the speaker.
    thanks. ka-9100 amp.png
     

     

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  2. gort69

    gort69 AK Subscriber Subscriber

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    I'm not sure what the 26.8V is in reference to, but look just to the left of the word "OUT" and you'll see 0V with an arrow pointing to module pin 5/board pin 7. See page 22 power amp schematic for a clearer view.
     
  3. rossm

    rossm AK Subscriber Subscriber

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    OK thanks, I am sure if 26.8v dc ever shows on pin 5 the power pack would be fried.
     
  4. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Location:
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    The 26.8V is the setting for the amp under an 8 ohm dummy load to calibrate the power meters to 90W. Adjustment (2) Page 21 of the service manual explains it.
     
  5. rossm

    rossm AK Subscriber Subscriber

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    Cool, now I understand!

    Bummer tho my right power ic is blown. Might be better off to part this one out
    Thanks
     
  6. rossm

    rossm AK Subscriber Subscriber

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  7. gort69

    gort69 AK Subscriber Subscriber

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    Don't assume the TA-100 is bad if you're getting a ton of DC voltage at pin 5 of the module. A shorted Qe5-8 can cause this and the module survive. There aren't many transistors on the amp boards - I'd pull and test them all. The tA-100s are pretty darn tough.
     
  8. rossm

    rossm AK Subscriber Subscriber

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    Hi
    I went back and pulled the transistors, Q11 and Q5 are ok and Q7 looks to be bad. I did check voltages on the ta-100 again with the 3 transistors removed.
    pin volts
    1 +1
    2 +58
    3 +34
    4 +49
    5 +37
    6 -58
    7 +31.5
    8 -50
    9&10 0

    I would think that pin 5 would be at 0v now, also not expecting 34v on pin 3. As a side note the speaker relay is now clicking on with the 3 transistors out of the ckt.
     
  9. gort69

    gort69 AK Subscriber Subscriber

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    I have a hard enough time understanding things with all of the transistors in place, and no clue what to make out of voltages with half of them removed.
     
  10. rjsalvi

    rjsalvi Active Member

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    Location:
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    Gort is right about all the transistors needing to be in place for accurate measurements. Also, a voltage check at the pins of the individual transistors is in order to effectively determine which ones are faulty. Your TA-100 could be hosed, but until you're sure the supporting cast is good or bad, you won't know. Also, high DC voltages are as a result of supply rail voltage, not the audio signal (AC). The 26.8V that Hopjohn refers to (for meter calibration) is AC voltage, not DC voltage. You can test the transistors out of the boards for a quick and dirty check of obvious errors, but an in situ test of voltages at the E,C & B is more thorough. Don't forget, the board has three diodes and a few electrolytics that if faulty, will cause voltage anomalies.

    I'm more curious as to why you have close to rail voltage on pins 4 & 8. Qe1 & 3 are (NPN) matched pairs as are Qe5 & 7 (PNP), so if you replace one of the pair, replace the other as well. When you think you have the supporting cast dialed in, start at the TA-100s and work your way towards the inputs looking for voltage anomalies. If you find one, it doesn't necessarily mean the transistor your checking is bad...it could mean a component in the surrounding circuitry has gone kaput. You just need to narrow it down and fortunately, the other channel works so you a valid comparison of measurements. When you nail it down -- assuming it's not the TA-100 -- you probably won't have exactly 0V DC on pin 5 of the TA, but if the voltage reading is low (mV territory), you can trim it with VRe1, to 0V.
     
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  11. rossm

    rossm AK Subscriber Subscriber

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    Hi rjsalvi
    Thanks for your input ! I agree with what you and gort69 are saying. I have been reading your thread and others on KA-9100 restoration, I must say you had quite a time but did manage to pull it off. I have placed a digikey order to replace the above transistors and caps the for the amp board. I also ordered enough parts to build the TA-100 replacement ckt.
    I will continue to post one I get the order in and start the repair.

    I did some measurements on Q5 and Q7, both transistors look fine measured out of ckt.
    Q7 The bad channel
    e 56.2v
    c 53.7v
    b 58.4v

    Q5 The bad channel
    e 56v
    c 19.3, maybe ce17 is bad or ???
    b 55.6v

    Q8 The good channel
    e 57.8v
    c 1.19v
    b 57.3v

    Q6 The good channel
    e 57.8v
    c 3.42v
    b 57.3v

    at least the preamp and tone ckts are working !
     

     

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  12. rjsalvi

    rjsalvi Active Member

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    (chuckling) Yeah, my 9100 popped my restoration cherry as I had to wrap my head around the circuit topology. Once you've done one, you start to get the hang of what's going on and see the similarities in other units. You will too! :thumbsup:

    At this point, I'd be inclined to change out Qe1-7. 1 & 3 are NPN, so a KSC-2690 will work there and Qe5 & 7 (PNP), can be subbed with the KSA-1220. Not the highest gain transistors on the block, but sturdy as hell. It's still possible the TA could have a short between pins 2 & 3, but you want to eliminate everything else first for obvious reasons ...(TAs are hard to come by!).
     
    Last edited: Feb 25, 2018
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  13. rossm

    rossm AK Subscriber Subscriber

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    I am back again, got my digikey order !!
    I have replaced q1 q3 q7 q5 all which checked ok on the transistor tester, I pulled q9 and q11 they also tested good, put them back in as I don’t have replacement. Replaced caps c3 c13 c15, c13 and c15 were supposed to be 47mfd but measured 8 mfd on my meter, Original c3 measured closer to spec than the new replacement. Tested diodes and resistors in ckt with ranges of what I would expect.
    Looked good on dim bulb. All voltages on the t-100 pins, were the same as before.
    Will take another look tomorrow

    7F14126B-F5BC-4607-ABD1-733416818394.jpeg
     
  14. rossm

    rossm AK Subscriber Subscriber

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    kenwood ka9100 power amp.png
    Did some more testing tonight. The service manual show 24v on the cathode side of D1, I have 46v. I also have 32v on the anode side of D1, shouldn't it be 0v ? the anode looks to be connected to ground.
    This part of the ckt has +B 58 volts coming in to R13 (I checked in ckt at 3.3k) R13 is supposed to drop the voltage down to 24v ?
    I get it now, the zener + R15 is supposed to drop the +B 57v down to 24v, which feeds ice1 and the base of qe5, am I right ?
     
    Last edited: Mar 3, 2018
  15. sajjad amer

    sajjad amer Active Member

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    Location:
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    @rossm have you got it sorted ? I am in same boat and wanted to know the solution IF you managed to find one?
    Thanks
     
  16. rossm

    rossm AK Subscriber Subscriber

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    Right now my plan is to order a new zener and see if that cures my voltage drop problem
    Stay tuned
     

     

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  17. DrumminDaddy

    DrumminDaddy Hit it, Baby !!

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    Did you mean zener + R13 , and base of Qe1?

    whenever I see a zener like that, I think “voltage regulator”. Yes, I’d definitely be replacing that 24v zener.
     
  18. rossm

    rossm AK Subscriber Subscriber

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    Yep good catch, just checking on who’s paying attention haha!
     
  19. rossm

    rossm AK Subscriber Subscriber

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    Having nothing better to do, I drove 3 hours today to pick up a ka9100 parts amp I found on Craigslist . Pretty rough. I bet it could tell some stories. But the price was right, passed dim bulb test, but no relay click. Voltages on the power amp pins look good. So now I have a plan b if my ta100 is bad. 8993B0E9-318D-400F-A2AF-21DBF24157BB.jpeg
    B66F0F01-6DE2-4877-9901-0863C642A9AF.jpeg
     
  20. rickl

    rickl Member

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    Location:
    Twin Cities
    Ross, looks like Zorro has been in there.

    probably a good idea if you need parts to get one running. Or with your new skills, you can get both working.
     

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