Dead transformer help identify and replace

Discussion in 'The Projects Forum' started by BFreemanNH, Jan 6, 2013.

  1. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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    Hi Folks,
    New here. I have a Cambridge Soundworks Basscube 10. It has a built in mono amp. The AC cord passes through a fuse (Test closed) and enters a 4" square transformer. I have no current coming from the secondary. I removed it and the transformer test with no resistance on the primary side. The secondary does have resistance. The board also looks burnt under the zener diodes. I was wondering if someone could help confirm that no resistance across any combination of the primary wires (4) is indeed bad, help identify a replacement transformer and maybe touch on what...or if anything on the circuit's secondary side could cause an open circuit on the primary winding. What other components should I suspect?

    Transformer is labeled: B3-038-1-76-F 8603074F FEDERAL

    It has a Black, Red, Orange and Brown wires on the primary
    and
    Blue, Black and Blue wires on the secondary.

    I tried searching google for this transformer, with no hits.

    Thank you for reading,

    Brad
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Does the TX has a primary over temp fuse.

    If you can't tell, post some pictures of the area where primary wires are going in to the TX.
     
  3. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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    Yes, it does state that it does, but I could not find it. I already figured it was toast. I tore it apart looking for a fuse of some sort. It looked to me that the primary leads go directly to the coil winding. I did not remove the secondary cover yet. I just figured it would be under the primary cover. I did not see any obvious damage under the insulation of the primary coil. at least, what little of that I can see.

    Would a picture help identify a replacement?

    https://www.dropbox.com/s/nelmzto0umg8y4f/DSCN0593.JPG

    https://www.dropbox.com/s/qsm64dxg55hsayk/DSCN0594.JPG

    https://www.dropbox.com/s/f32cru1r8vm6tit/DSCN0504.JPG
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    See the wire between orange & brown.

    Check resistance between that wire to orange & to brown. post the results.
    Further you can check the resistance between each wire
     
  5. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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    Thanks for taking interest in this R!@@.
    Orange=5.8Ohms
    Brown=Open
    Between the two bare wires=Open
    How could this ever be checked without cracking the TX open? Where is the thermal fuse, buried in the windings?
     
  6. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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    Anyone? I mostly would like help identifying a suitable replacement. It is powering a 75w amp. Is it able and worthy of being rebuilt? Can anyone point me to a decent transformer repair shop?
     
  7. Meixner

    Member

    Sep 26, 2011
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    21
    The thermal fuse should be connected to the hot wire on the primary side. They are usually in the outer winding just after the wire connection. Try cutting away some of the insulating tape with a x-acto knife or a razor blade.

    To find a replacement you would need to identify the secondary output voltage and take a guess at the amp rating.
    It may not be worth replacing because the amp board looks pretty worn out and there may be something shorted there that caused the fuse in the transformer to blow.
     
    Last edited: Jan 9, 2013
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Ur post is complete.

    Unless you measure the resistance between all the wires I cannot tell you how to bypass the thermal fuse
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yep they are often buried in the primary winding, and can't be repaired by anything less than a total transformer rewind by a pro shop.

    However, most audio amps use fairly standard voltages, and it is quite likely you can find a "good enough" replacement transformer once we know more about the circuit.

    Any photos, specs, or manufacturer schematic would help to decide on a replacement transformer.
     
  10. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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    It sounds like I am kicking a dead horse. Due to all the burn marks around the zener diodes and main resisters, plus the dead transformer, maybe a new solution is needed to drive this 10" 75w basscube. Can anyone suggest a power and audio kit to drive this speaker? It is fed by a mono jack coming from my Onkyo receiver. Might be a good learning experience for me.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Do u really think tht ur amp pcb is toast.

    Or is it just the PCB is just heated too much and the components may still be OK.

    Did u checked them, the zeners and all.
     
  12. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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    I did pull them and checked them on a fluke. They all passed, as well as the resistors. I just bought the PEAK Atlas component and ESR analyzers, so I will be checking everything. Even if it is just for the experience.
    I still can't find any info on the transformer and I just don't have enough knowledge to even begin to guess what transformers might work.

    I was thinking something like this Kit might work: http://store.qkits.com/moreinfo.cfm/FK666
     
  13. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Photos are needed! Transformer watts can be determined by the physical size, and the transformer voltages are pretty standard and we might be able to work that out based on what amp chip is present. Also the photos will show if the transformer has other voltage outputs like +/-15v rails for the preamp.

    Heat marks around the diodes etc on the PCB are common, it probably means the amp has been worked hard with little ventilation.
     
  14. bratsuzao

    New Member

    Jan 11, 2013
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    Does the TX has a primary over temp fuse[​IMG]
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Most of them has.
     
  16. BFreemanNH

    Thread Starter New Member

    Jan 6, 2013
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  17. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Wow! Looking at all the severe overheat evidence on that second photo;

    [​IMG]

    I would worry about the reliability of that amp. It's possible the amp chip shorted and cooked a heap of other things, and finally the transformer too. Personally I would prefer to get a nice new amp than to source a transformer for that one and try to fix any other damage!

    By the way dropbox.com sucks, I had to hack their source to get the picture without it spamming tons of tracking cookies and other slow as hell invasive crap all over my PC. The forum has an "attachments" option that lets you attach photos direct from your computer without needing to resort to using a nasty 3rd party photo hosting service.
     
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