SMPS Charger Problem

Discussion in 'General Electronics Chat' started by hazim, Sep 14, 2012.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Dear all.

    Hope you are fine, I didn't open the forum from a while...
    I'm trying to repair a 13.8V charger of a 600W inverter... The charger board is separate from the inverter board, as you see in the picture.

    The charger has a 1000μF 25V capacitor at output, and it has a trimmer pot. to calibrate the output voltage between 13V and 14.5V (approximately). The problem now is that when I connect the AC input to the mains (220V), the charger should work fine and outputs 13.8V apprx., but it gives about 40V instead and the 25V output capacitor become hot of-course and tends to explode.. but I disconnect the mains plug instantly, and I find a 2C945P transistor became bad and I replace it...

    As you see the components on the board, I replaced the rectifier diodes at the AC input the first time I tried repairing, they were shorted, and I replaced the 2SC945 and a high voltage MOSFET at that time, I replaced it later too as it shorts when I try if the board is well repaired. The problem wasn't solved.

    There is a microcontroller, I replaced it with a new one from another similar board, and replaced the transformer with a similar one too, and replaced the optocoupler and the triac\diac? with similar ones, but the same problem still exists. Ofcourse I tested the remaining parts (diodes, resistors, capacitors) and they are not many by the way... it's a small board.

    I replaced the whole board with a new one and it worked fine, so there is some problem in that board.

    In conclusion, I almost replaced the main parts with similar new ones, and tested the other parts and replaced some of them, but still didn't figure where is the remaining problem... Any recommendations or help is strongly appreciated.

    Regards,
    Hazim

    [​IMG]
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
    744
    any chance of a schematic or circuit diagram,
    what is the model number of the psu?
     
  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    No chance... I tried very hard but didn't find.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
    744
    The small pcb is that the one with the fault?

    Any model number?
     
  5. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Yes the small one. I can't find a model "number" written/printed on it but there is "UP_AD_H_E" printed on it, maybe this is it.
     
  6. Guinness

    Member

    Dec 31, 2009
    81
    1
    Hi,
    You said you replaced the transformer and controller with a similar board, are you sure they are the same?
    I don't mean that in a rude way, but I repair smps every day at work and have found that similar boards of the same make use slightly different parts.

    Also what controller is it? you said microcontroller, just curious as to what it is?
     
  7. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Yes they are the same and I'm sure about that. Tomorrow I'll see what is the controller exactly because I'm home now and not at work where I'm repairing the inverter's charger.
    I think it's used as a pwm high frequency (ex. 100kHz) driver for the transformer.... not sure as that can be easily done by few transistors.
     
  8. Guinness

    Member

    Dec 31, 2009
    81
    1
    I only ask as its normally a smps controller, not a microcontroller thats used. But either way you could supply the voltage required to the IC to activate it and scope the output to make sure the wave form output is correct without risk of damaging anything on the circuit.

    But if its possible to get a more detailed picture of the board that would be usefull, preff a few close close up pics.
     
  9. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    The controller/uC is ELAN EM78P156ELPJ-G ( datasheet )

    You can see the attached pictures for more details.
    There is a 7805 IC feeding the controller and I'm sure that the IC is good and the waveform is correct because it worked fine on another board.

    Regards,
    Hazim
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
    744
    Looks like the track has been blown running under the opto couplers to the diode(D8) and transistor(Q6) at the corner.
    or is it just the flash off the camera?

    img 12.35.36.jpg
     
  11. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    it's the flash of the camera, the board and tracks are okay.
     
  12. Guinness

    Member

    Dec 31, 2009
    81
    1
    There really is not alot on the board!
    The only thing I can suggest is check all the components again, how far you want to go is up to you and what test equipment you have.

    One thing I would suggest is to replace all electrolytic capacitors even if they test good. Have had ones that read fine on capacitance test and esr test but break down under load in circuit.

    If you can try testing the diodes and resistors under load out of circuit, to make sure they are not breaking down under load aswell.

    Im not sure how old your unit is, but have had all the above test fine but break down when power is applied to them.

    Also if you dont have a transistor tester, you could try replacing them as a last effort.

    Could also try metering out the tracks, could be a crack in one that you cant see.
    If you have a scope with a component tester built in, saves a lot of time.

    There are a few suggestions, but best way to test is if you can power up parts of the board and simulate working conditions and measure what you get. Things like power up the IC, scope the oscillator input, scope the output and where it is going to.

    You should be able to power up all the control circuitry on the board without needing the mains and work safely with it, assuming you have a variable power supply and scope this is...

    Good luck anyway, a few things to keep you busy at least.
     
    hazim likes this.
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