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KR-2300

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by MyLastWord, Aug 5, 2018.

  1. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    Does anyone have a Kenwood KR-2300 receiver, could help me to find replacement/equivalent for the power transformer. I believe it's toasted, since I check the voltage on the secondary and got no voltages reading. I couldn't find any service manual except the attached schematic. The primary have the Red&White. The secondary have 2 reds, 2blues and 1black wire. The marking say L05-0029-05 and 7S3Z6 and nothing else.
    Greatly appreciated.
     

    Attached Files:

     

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  2. chazix

    chazix AK Subscriber Subscriber

    Messages:
    1,163
    Location:
    Groton MA
    I don't have the receiver, but in case nobody comes along with actual measurements, you could estimate the center-tapped secondary voltage thus: The voltage of the bulk DC supply is given on the schematic, 47V. So, each half of the center-tapped secondary must be providing 47/sqrt(2), or about 33V. I think it's safe to assume that the schematic voltage is with minimal loading, so pick a transformer that's rated somewhat lower than that estimate - maybe 32-0-32 (or equivalently, 64VCT, or two separate 32V secondaries). Transformer power rating should be something like 2 times the total output power that the receiver is rated for (the sum of both channels).

    The other secondary is a little easier - the schematic gives it as 7.5V. It supplies all the lighting, so if you're retaining the incandescent lamps, this secondary should have a current rating of something like 2A.

    I don't think you'll find a single transformer with the appropriate secondaries, so you'll probably need to find room for two transformers.

    HTH,

    chazix
     
  3. savatage1973

    savatage1973 Addicted Member

    Messages:
    6,403
    Location:
    NW Pennsylvania snow belt
    Unless you can find a really cheap "donor" unit, you are probably not going to find a transformer that meets those specs for equal or less price than the value of the whole unit.
     
  4. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    Thanks for the great info and analysis to both Chazix & Savatage. I am probably going to frankentize the power supply for this unit as a a project then.
     
  5. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    21,490
    Location:
    SE PA
    Did you check for continuity of the primary? Scat shows a thermo fuse.

    Do you have continuity on any of the secondaries, the blues for lamps or the red to black.

    would be a nice project to build a ps for the unit.
     
  6. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    I took (cut the wires) the transformer out of the unit already and just check for continuity on the 2nd as follow:
    red-red=yes. blue-blue=yes. both red-black=yes. both blue-black no.
     

     

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  7. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    21,490
    Location:
    SE PA
    Red and black are the power for the unit. Top of wave red, bottom of wave red, center tap black so your secondaries to drive the unit are good.

    The blue only drives the lights and it is two blue according to the scat. And that is good, too.

    Check the primary. I believe you have an open thermal fuse built into the transformer and that should show open. If it too has continuity, the transfo is fine.
     
  8. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    Dummy me, never suspect the primary side. Turn out they are bad, opened, no resistance. I think the 2ndary are fined.
     
  9. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    21,490
    Location:
    SE PA
    Teh scat says there is a thermofuse in that primary line. maybe you can find it and replace it.
     
  10. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    Just googled, youtubed and learn about thermal fuse in the transformer. Now I need to learn how to dig it out.
     
  11. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    Thanks Blue. I just learned from you something new about thermal fuse in transformer.
     

     

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  12. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    20180805_210008[1].jpg
    Pried open, reveal naked transformer on the primary side. Can's see anything remotely look like thermal fuse. May be it bury deep in the coil.
     
  13. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    20180805_211242[2].jpg
    There it is. In the middle, silver thing with little wire poking out. Fair to say I have destroyed this TF. It's the primary side and have no confident of fixing this.
     
  14. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    20180805_212551[2].jpg
    Or may be I could fix this. After cutoff the two end of of the fuse connection, leave the bottom wire of the TF. Now the is continuity be the bottom copper wire of TF and the top red. Could I go without using the thermal fuse? or Should I put a fuse in between? is it OK to leave the dead fuse (trimmed) in? What spec of the new fuse should be?
     
  15. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    581
    Location:
    San Diego, CA
    If you can, you should R&R (remove and replace) it. The specs will be on the body of the fuse. Why is it there? If the windings short, the TF may not draw enough current to blow a power fuse, but could reach temps high enough to cause a fire, so the fuse protects from that. Temp goes up, thermal fuse blows. Can you short it with a piece of wire? Yes, but...see the part about the potential for fire. Should you decide to pursue the latter, you're on your own and were warned...not necessarily because it won't work, but because I assume no liability. ;) How does one re-tape the TF? 3M, maybe others, make what's called "margin tape" (transformer tape) and there are a couple different (temperature rated) grades, mylar and kapton ... kapton being the higher temp rated. IIRC, it has adhesive on one side.

    The other option is to be patient and find a donor KR-2300.
     
  16. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    21,490
    Location:
    SE PA
    There we go, dig into a not repairable, inexpensive unit and sacrifice it as needed to learn while taking care to not completely destroy it so is could possibly be returned to service.

    I have no idea of the fuse in the unit and I doubt Kenwood made known what this is but as posted above the fuse should be labeled. What I would do is post on the DIY board or the SS board a question about that fuse with the info you know about the situation and the link to the scat. Maybe someone knows what you might be able to use to replace that fuse, I would replace that fuse. Someone on ak knows about thermal fuses and if you can find number on it that would be great. If not, maybe they can suggest something.
     

     

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  17. MyLastWord

    MyLastWord New Member

    Messages:
    28
    Location:
    Brampton, Ontario. Canada
    Thanks everyone. The TF for the unit is wrecked. Very unlikely I am going the find the replacement for this unit. In the meantime I will use as spare/parts. Fellow AKs are welcome to any parts from this unit as long as you willing to pay for the shipping cost.
     

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