Blown fuse on KA-6100 upon power up.

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by beer_me, Mar 31, 2018.

  1. beer_me

    beer_me New Member

    Messages:
    35
    Location:
    Oregon
    I finished recapping and cleaning my very dirty newly acquired ka-6100. The fuse in F1 blows every time I power on. I tried twice just thinking the first time was a fluke. It’s a 250V, 4A fuse.
    I have tested the transistors, they at least meter out good. Should I replace them even if they seem good? I made sure Cm 81 was replaced with a bipolar cap too. Can anyone point me in a direction to troubleshoot? Thank you in advance
     

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  2. Duffalora

    Duffalora Active Member

    Messages:
    218
    Location:
    Auckland, New Zealand
    Suspect power supply issue. Check all diodes on the F1 side.
     
  3. rjsalvi

    rjsalvi Active Member

    Messages:
    477
    Location:
    San Diego, CA
    You'll need a DBT to handle the short so it doesn't domino. Did the fuse blow before you'd worked on it? What transistors did you check?
     
  4. mgkfifty

    mgkfifty Active Member

    Check for solder bridges/caps in backwards.
     
  5. beer_me

    beer_me New Member

    Messages:
    35
    Location:
    Oregon
    I'm going to have to build a DBT. The fuse only blew after I worked on it. I only tested the main power transistors so far.
    All caps are properly oriented. Checked for solder bridges, haven't found any.
    I just noticed that Cd27 (.047uf) is missing from the pre-amp board. Per disassembly instruction, pictured below, that should be removed to take apart unit. It never got put back and the two points on the PCB were just soldered.
     

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  6. rjsalvi

    rjsalvi Active Member

    Messages:
    477
    Location:
    San Diego, CA
    Are the "main power" -- I assume output transistors -- in the correct slots?
     

     

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  7. beer_me

    beer_me New Member

    Messages:
    35
    Location:
    Oregon
    yes they are, and they tested out fine.
     
  8. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,428
    Location:
    uk.. the middle bit
    make sure output transistors collectors are isolated from heat sink
     
  9. beer_me

    beer_me New Member

    Messages:
    35
    Location:
    Oregon
    The transistors are isolated with new mica insulators.
    The diodes on the F1, I read 5.7 from anode to cathode, a slow climb to OL from cathode to anode using my diode function on my meter. Are these ok? They all read the same way, from F1, F2 etc.
    I've started testing other diodes. found two to not be bad - Dm19, & Dm18 which is a W06B shows 0.0 at anode and cathode. Neither side is OL.
    All of the other diodes function as normal.
    Still wondering what's going on with the cap from the disassembly pictured above too. Could that be giving me problems?
    Thanks for the help thus far guys!
     
    Last edited: Apr 1, 2018
  10. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    994
    Location:
    Vancouver, WA
    I don't trust in-circuit diode tests - are you lifting one leg to test?
     
  11. beer_me

    beer_me New Member

    Messages:
    35
    Location:
    Oregon
    Only lifted the ones where I got bad readings to double check. Those were d18, 19. I didn't lift the diodes on the Fuse circuits.
    Also found that the ground wire from cap c27 to the chassis (that I referred to above) was missing so I resoldered that.
     

     

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  12. JG777

    JG777 Active Member

    Messages:
    107
    Had the same issue with a 7100, its pretty much the same setup, it was 2 shorted output transistors for the right channel. of course it was my fault for accidently shorting the positive speaker termianl to ground for a couple seconds.
     
  13. beer_me

    beer_me New Member

    Messages:
    35
    Location:
    Oregon
    Uh oh. Did you get it back up and running?
    I ended up pulling all of my diodes and testing. Most are being replaced. Two each from the rectifiers.
    Also going to replace the output transistors I suppose. Should I even if they test out fine? I now understand they can have leaks at the junctions and low current gain after so many years. Now that I think about my relay never clicked when I first powered up.
    All I'm finding for equivalents are: for the 2SA980=NTE281, 2SC2260=NTE280. Anyone have any others theyve used to replace?
     
  14. JG777

    JG777 Active Member

    Messages:
    107
    Yes that's what it was & I was selling it on eBay, sold it. As far as diodes in the power supply if they test good in circuit they are good, I really don't get why some people replace diodes, they don't age, either they work or they don't, end of story. Never had to replace a diode that tests good, ever in 40 years of repairing. The 7100 had no relay engaging either when I got it, it was a 100uf cap in the preamp power supply open. Power supply caps are the first things to look at. I have a 6100 that just needed controls cleaned. The 7100 had NTE 280 & 281s some people on here don't like NTE stuff which really kinda pisses me off, never had a problem with them, Newark sells them. If your transistors test good & not shorted they most likely are good, no shorts to the case on either leg or between legs when tested with a diode check. I also don't get why some people replace transistors because they are old, like diodes, either they work or they don't. I don't do that & find it totally unnecessary.
     
  15. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    19,721
    Location:
    SE PA
    The NTE are possibly unknown transistors that kinda meet the specs of the NTE numbers. I don't know if they are the best for the amp. I did look up the c2260 here on ak with a search and there were a few recommendations for the MJ15something transistors. I would look into those first as they are a specific transistor, not that the NTE isn't but the NTE could be something else by someone else the that NTE sells to fit the c2260 and probably a few others.

    Just search ak for either of the original Kenwood transistors and get the numbers for the MJs.
     
  16. JG777

    JG777 Active Member

    Messages:
    107
    I ran the 280 & 281s for 3 days of music before I sold it & the guy who bought the amp is very happy with it. Don't know why u say they aren't the best for the amp, they are the cross reference part for the transistors in the 6100, 7100. They work & they sound good so what is the problem? Stop listening to AKers who don't like NTE. Yes there are other subs but.......whatever.
     

     

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  17. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    19,721
    Location:
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    I believe you mean that are the NTE cross reference part for the transistors used in these amps.

    My concern is from the way that NTE normally works. They have transistors they have bought and they match them to spec sheets for different devices and then claim they are the cross referenced part (of their offerings) that will work. I would expect most times they work just fine. Others maybe not so well. But NTE not manufacturing the devices vs. current production from one of the parts suppliers where you match up the specs and select one...could be the way to go. I'm glad to see that the NTEs worked for you. I would only consider them if there wasn't something from a manufacturer available, well I mean, unless I didn't find a good substitute vetted by some here on AK or elsewhere that is a recommended part such as the MJ15015 and MJ15016 in this case. Just that NTE is a latter resort then Mouser/Digikey new parts.
     
  18. JG777

    JG777 Active Member

    Messages:
    107
    Wow you are really really getting too carried away with this transistor topic & this is the last response I'm going give. Compare the data sheets, the 2sc2260 is listed as a "general purpose switching transistor", the 280 is listed as a "audio power amplier transistor" 280 has more power dissipation, 100W compared to 80W, more collector current, 12A, CE & CB voltages of 140 & 140, 160 & 100 on the 2sc2260, sorry but the 280 & 281 is a better transistor DESIGNED for audio power amplification. It's better than those that came in the 6100 &. 7100. Don't know how you can just say they aren't right for the amp. The 284 & 285 also replacements for blown 2sc1116a & it's compliment, Newark isn't going to sell you shitty transistors that aren't within the specs. To replace blown 2sc2260 & 2sa890s1! Sure there are Fairchild, Motorola & a couple others, NTE has been around for a long time & wouldn't be in business if it wasn't Thier business. "Recommended replacements by AK"?, hey no matter which replacement u choose it's better than what came in it from the factory. There are a lot of know it all types on AK, the "audiophile" types who think you have to spend 5 grand on a turntable & this capacitor "sounds better" than the other, most of it I just ignore, ive learned a lot on here & been helped & helped others, but I think some of these people just get nit picky & act superior, oh well. That's my rant.
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,428
    Location:
    uk.. the middle bit
    i would like to see the data sheets for those NTE transistors
     
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  20. JG777

    JG777 Active Member

    Messages:
    107
    It's readily available on the NTE Cross-reference site :http://nte01.nteinc.com I use this constantly & have for years to check what component is the same as another, some u can't find but most u can. Just type in the part # u have then a cross will come up, not 100% accurate on everything but close. It's another tool.
     

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