Dead Transformer of a Guitar Amplifier

Discussion in 'General Electronics Chat' started by aq_rules, Dec 29, 2013.

  1. aq_rules

    Thread Starter Member

    Oct 28, 2009
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    I have Fernandes Orange sonic Os-15(model no.)

    It needs a 100/110 volt input..
    In my country we have 220 50hz main so i was using a power supply/stablizer type of thing..anyways it was working perfectly but yesterday the amplifier wasnt working so i checked it and got to know that the transformer isn't giving output to the circuit..(i have checked input, 110volt is passing through the transformer but no output)

    I have detected the problem but i dont know the SPECS of the dead transformer.


    My question is:

    1) How to know what output is needed from the transformer so i could replace it with new one?

    2) Is there any way to repair it (if i couldnt get the same transformer in market)?

    3) Is it possible to replace a transformer of 220 volt input and output same as required in the circuit?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Are you sure you checked right at the transformer secondary, it is possible that a winding went open, but very rare.
    Is this a transformer in the Amp itself or the external system you have in place for the 220-110v?
    If it is the external unit, a 220/110vac transformer is quite common.
    Max.
     
  3. aq_rules

    Thread Starter Member

    Oct 28, 2009
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    The external system converts the 220 mains to 110...the external system if working perfectly...
    Lets forget the external supply.

    The transformer inside the guitar amplifier is the problem...it takes 110 input...but i dont know what output it gives to the circuit...i want to know output by this transformer..i have checked it correctly it gives no output
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Can you still measure the resistance of the 110 Volts coil of the transformer?
    If not, it can be that the (thermal) fuse inside the transformer is gone.

    Bertus
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    Can you get a schematic?
    Details would help.
    Any markings on the transformer?
    How many wires on the secondary?
    Can you post some clear photos of the transformer and power supply section of the PCB?
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  7. sheldons

    Active Member

    Oct 26, 2011
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    thermal fuse may be the problem with your transformer-its not too hard to find and replace if you are careful
     
  8. aq_rules

    Thread Starter Member

    Oct 28, 2009
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    Three wires on the secondary...black and two red...

    Black and red(secondary) shows continuity at X1 ohm meter..

    The input wire of 110 volt at primary does not deflect at all at the X1 on ohmmeter..

    What is thermal fuse and how to get to this...need to open the transformer??
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you are lucky you may see two connections sticking out of the primary (Inner) winding, you may have a big problem pulling it out, at a last resort connect the to ends as long as you identify this as the fuse, and fit a suitable fuse in the primary input supply.
    This is all assuming that it not only has a thermal fuse but you identify it correctly!
    Max.
     
  10. aq_rules

    Thread Starter Member

    Oct 28, 2009
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  11. aq_rules

    Thread Starter Member

    Oct 28, 2009
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    [​IMG]
    [​IMG] transformer
     
  12. aq_rules

    Thread Starter Member

    Oct 28, 2009
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  13. aq_rules

    Thread Starter Member

    Oct 28, 2009
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  14. aq_rules

    Thread Starter Member

    Oct 28, 2009
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  15. aq_rules

    Thread Starter Member

    Oct 28, 2009
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  16. inwo

    Well-Known Member

    Nov 7, 2013
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    Almost always the case.

    Un-form the metal covering and remove.

    Carefully remove cardboard layers. Only get one shot! Be very careful.
    Primary wires will be the size of a hair.

    When you find the thermal fuse it will have larger wires connected to it.

    Connect the two wires together.

    Power transformer with a small fuse for protection.

    Read secondary open circuit voltage for referencing a replacement.
     
  17. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Not a good idea. If there is a "thermal" fuse in the primary winding, it was there to open with too high a winding temperature. A standard "current" fuse in the line does not serve the same safety purpose.

    And as I said before, a transformer designed for a 60Hz will likely fail when operated near its ratings in their 50Hz power system.

    Ken

    Added. Since the label said 50/60HZ, my comment about that is moot.
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have found they fail through normal trivial current inrush, fatigue etc.
    As long as they are fuse protected at the transformer rating there should be no problem, There was a time when many Asian made transformers had these, unfortunately they were embedded in the winding with no chance of replacing, on an otherwise good transformer.
    Max.
     
  19. aq_rules

    Thread Starter Member

    Oct 28, 2009
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    Cant we just guess the output by studying components on the circuit...like JRC 4558D Op Amp used has operating voltage value ranging from 4v to 18v...

    And capacitors of 25v 2200uf?

    My guess is , it would need 16-18volt....but what about the current?
     
  20. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Yep.
    That's why I suggested the photos. Voltage and current requirements would depend most on what appears to be a 5-pin amplifier chip mounted on the heat sink. (Maybe a TDA-type) And, the photo in post 14 shows a 13W input power.
     
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