Can I swap an internal PSU with an external power supply

Discussion in 'Technical Repair' started by David Evans, Jan 9, 2019.

  1. David Evans

    Thread Starter New Member

    Jan 7, 2019
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  2. BBee

    Member

    Dec 6, 2018
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    Without getting too involved in the problem, any set of subfuntions of any equipment can be regarded as black boxes, taking defined inputs and processing these to give defined outputs. As such, if any subfunction is removed then it can be replaced with the black box which, having all previous connections connected, functions in the same way. In essence the power unit can be replaced by an external unit, but realise that it must provide identical functionality. This means, along with the obvious volts / amps/ ripple currents etc, to be identical such things as stay pickup from longer leads etc must be taken into account. They may or may not be a problem.

    Tracy
     
  3. David Evans

    Thread Starter New Member

    Jan 7, 2019
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    Thanks Tracy,

    Conceptually I couldn't see why not, but wanted to check that I wasn't missing anything.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The declared wattage is 60w which is not all that much.
    Max.
     
  5. David Evans

    Thread Starter New Member

    Jan 7, 2019
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    Yes it is simply a mixer of 2 audio channels with basic filtering and no amplification.

    So I found a service manual and identified where the transformer supplies DC power, but these are just labelled as S1+, S1-, S2+, S2-, COM and no labelling of output voltages. How do I identify what the voltages should be in order to check if this is correct?

    Thanks



    Screenshot 2019-01-12 at 20.50.18.png
     
  6. absf

    AAC Fanatic!

    Dec 29, 2010
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    The real meat is in the "D Block" which carries the transformer and voltage regulators. Doesnt look too complicated to me.

    Why did the technician said that it was beyond economical repair? Unless the transformer is faulty and a new ones is too expensive or the real fault was not in the power supply and it was too expensive to buy a new PCB.

    You have to find out what are the voltages of S1-, S1+, S2= and S2+ ay J702 before you can proceed with the use of external power supply...

    Allen
     
  7. David Evans

    Thread Starter New Member

    Jan 7, 2019
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    Hi Allen,

    They didn't look at it, but just assessed that if changing the fuse over didn't fix the problem of being plugged into 240v while on the 110v setting, then it would cost more for him to repair than buy a replacement 2nd hand model.

    Do you mean what they currently are, or what they should be? I was trying to determine what they should be, but it wasn't obvious due to my lack of subject matter knowledge.

    I have attached the complete service manual as it may take a few seconds for someone who knows what they are doing to understand what the voltages should be at J702

    Thanks


    David
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Wich version of the mixer do you have?
    There are the KUC and SYL versions mentioned.

    In the schematics the module D is a bare transformer.

    pioneer_DJM_supply.png

    Bertus
     
  9. David Evans

    Thread Starter New Member

    Jan 7, 2019
    11
    1
    Hi,
    It is the SYL version (mulitvoltage).
    Yes the D module is a basic transformer attached to a circuit board - no other components. I have measured 237 AC volts into the hot side.

    S2+/- are reading 4.8v, whereas S1 +/- are only reading 0.16 volts. An educated guess is that this is the problem as I don't expect a DC circuit to be able to run on voltage that low, but I don't know what it should be.

    Thanks
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I would expect a voltage of about 12 - 15 Volts AC between GND and S1-.
    I would expect a voltage of about 12 - 15 Volts AC between GND and S1+.
    I would expect a voltage of about 6 - 8 Volts AC on S2+/S2-.

    Bertus
     
  11. David Evans

    Thread Starter New Member

    Jan 7, 2019
    11
    1
    Oh

    Of course it just just a voltage transformer so it will be AC output

    :oops:



    So this suggests transformer is actually ok and problem elsewhere or is that AC power too low?

    Thank you
     
  12. LesJones

    Well-Known Member

    Jan 8, 2017
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    It looks like the transformer has a built in thermal fuse on the primary. With NO POWER CONNECTED on board D (Transformer board.) measure the resistance from the right hand bottom terminal on the 3 pin connector (I think it is marked 3) to the top terminal on the the right hand two pin connector (I think it is marked 1) You should get quite a low resistance reading. If you get a high reading the thermal fuse in the transformer has probably failed.

    Les.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Can you measure the voltages again with the connector J702 taken of the board?
    Measure the voltage on J702.
    To me it sounds that the voltage on S2- / S2+ is to low with 4.3 Volts,

    Bertus
     
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  14. David Evans

    Thread Starter New Member

    Jan 7, 2019
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    Hi Les

    i get 288 ohms from 240v input (1) to ground connection (3)

    Thanks
     
  15. LesJones

    Well-Known Member

    Jan 8, 2017
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    288 ohms is higher than I would expect unless it is a very small transformer. Measure the resistance from the right hand top terminal on the 3 pin connector (I think it is marked 1) to the top terminal on the the right hand two pin connector (I think it is marked 1) I would expect this to be about 144 ohms as it is between the 120 volt tap and the 240 volt tap. I think doing what bertus suggests in post #13 should be your next step.

    Les.
     
  16. David Evans

    Thread Starter New Member

    Jan 7, 2019
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    I get 227 ohms for this. I attach pic of size of transformer for ref
     
  17. LesJones

    Well-Known Member

    Jan 8, 2017
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    Thank you for putting the AA cell in your picture to give a sense of size. The value of 288 ohms for the whole winding is a bit higher than I would expect for that size of transformer. That in itself would make me unsure of if the transformer was good or bad. The fact that one half of the winding measures 227 ohms and the other half 61 (288 - 227) ohms makes me think the transformer is faulty. It is more normal for a failed winding to have a very high resistance. Wait and see what the others replying to this thread think.

    Les.
     
  18. David Evans

    Thread Starter New Member

    Jan 7, 2019
    11
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    Ok measured again

    This time came up with following:

    S1+ 16.1v
    S1- 16.1v
    S2+ 8.5v
    S2- 15.1v

    Not sure what changed other than isolating from main circuit board.
     
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  19. David Evans

    Thread Starter New Member

    Jan 7, 2019
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    Thanks Les
     
  20. LesJones

    Well-Known Member

    Jan 8, 2017
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    The results from the S1+ - GND - S1 - winding suggest that the transformer is OK
    I think on the S2 winding you measured with respect to GND. That is not meaningfull a GND has no connection to the S2 winding. You need to measure between S2+ and S2-
    It looks like something on the main board has been damaged and is drawing too much current which is pulling the transformer output down.
    Les.
     
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