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Replacing a faulty SMPS

Discussion in 'Troubleshooting and Repair' started by HellasTechn, Feb 13, 2016.

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  1. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Dear friends,

    I have in my hands a Whirlpool L1373 (invensys 475560 board from a washing machine. The PSU on the board is damaged, blown capacitors, LNK304PN switch chip, and a broken (broken leads) smps transformer marked 13ES-X33.
    My problem is that it is impossible to find a replacement transformer so that i can make the board work.

    After digging into it i found a schematic of the board's PSU and i thought that maybe i can replace the original psu with a linear symmetric psu. According to the schematic the board requires -5Volt and -12Volt. I came up with the following circuit "see attached picture". What do you think ?

    Would it be possible to find such transformer somewhere or proceed with my plan <<B>>?
     

    Attached Files:

  2. HellasTechn

    HellasTechn

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    Apr 14, 2013
    After taking a closer look to the schematic i noticed that it uses mains phase as common rail so i now seriusly doubt that i can replace the psu.
     
  3. HellasTechn

    HellasTechn

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    Apr 14, 2013
    I dont know what to do. I am thinking that if i could somehow find a transformer or a transformer cell to wind up (i have the old transformers wire).
     
  4. ramussons

    ramussons

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    Jun 10, 2014
    I doubt if the "original" schematic is in order. Did you trace it or was it available as a drawing?

    It's not possible for the electronics in a washing machine to be "hot" wired.

    Even if it is :eek: , you can technically connect the "common" of "your" power supply to the "phase".

    I will NOT do it. :D
     
  5. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    The transformer will not be faulty.
     
  6. 73's de Edd

    73's de Edd

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    Aug 21, 2015

    Sir Hellas . . . . .


    DEFINITELY . . . . . No transformer for me either . . . . . with its mere 142 turns on the primary of #22 and even less on the secondaries of 7 and 3 turns of #26.

    Do a preliminary test of all diodes and electrolytics and then get one of these and go-for-it.

    http://www.mouser.com/ProductDetail/Power-Integrations/LNK304PN/?qs=sGAEpiMZZMupfmEBr0XgrOI/ieMCUyJmm4rcOZfpuIU=

    Mouser Europe should have them also . . . they makee velly - velly cheeeeeeeeep.

    ASIDE:
    Are they actually using negative voltages on the secondary supplies, and you are using common ground symbols freely, between
    the secondary and primary.
    Since this transformer definitely provides isolation between the AC line and the transformer secondary circuitry, usually there is
    only an interconnection between hot circuitry/ to cold circuitry via a static ground associated with the secondary as is being provided by
    a 2 megohm, or so, resistor and a low value shunting capacitor used bypassing the AC element.

    ASIDE_ASIDE:
    " (i have the old transformers wire)." . . . . .OOOOOPSIES !

    73's de Edd
    .
    .
     
    Last edited: Feb 14, 2016
  7. HellasTechn

    HellasTechn

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    Apr 14, 2013
    No i found it online.
     
  8. HellasTechn

    HellasTechn

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    Apr 14, 2013
    The transformer was not faulty i accidently pushed it and its legs on the primary side came off. The wire is cut and it is impossible to be repaired.
     
  9. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Dear 73's de Edd,

    i do not understand what you say in this post about the ground symbol and the transformer's wire.
    I did not draw the schematic i just found it online if you are reffering to that.

    The board is complicated and it is not easy for me to make a the schematic.

    What appears to be the primary side of the transformer is connected to pin 5 of the LNK304PN and the other pin goes to Mains through resistors diodes and a coil (that looks like a resistor externally).

    Does that help you figure out ?

    I have to be away on busyness for 3-4 days, after i come back i will desolder the rest of the components on that side and take pictures. that might help.

    thank you all for writing back ! Any comments WELCOMED.
     
    Last edited: Feb 14, 2016
  10. HellasTechn

    HellasTechn

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    Apr 14, 2013
    P.S. I do get the feeling that the schematic may be wrong. I think that as reference point (0V) the neutral side of mains is used or diodes D29 and D30 should be facing the other way right ?
     
  11. HellasTechn

    HellasTechn

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    Apr 14, 2013
    I have already done this and found bad capacitors.
     
  12. Alec_t

    Alec_t

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    Jul 7, 2015
    I share ramussons's doubts as to the accuracy of the schematic. For safety reasons, don't rely on it.
    A linear supply should be ok, providing you don't need to draw high current from any of the outputs. Alternatively, SMPS supplies of appropriate voltages are probably cheaply available off the shelf.
     
  13. HellasTechn

    HellasTechn

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    Apr 14, 2013
    My concern is about the mains line being present in the output because i cn see that the capacitors on the output have their positive side connected on the same line as the varistor. the capacitors polarity could be explained if the output voltage is indeed negative

    If a mains rail is indeed used as reference point for the negative supply voltages then i can not use my linear transformers center tap as reference point for the output voltages.

    I could possibly disable the mains input of the board but then the machine will not work since mains is fed through selector switch and alo from on board relays feeds other components such as the heating element and the motor.
     
    Last edited: Feb 14, 2016
  14. Alec_t

    Alec_t

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    Jul 7, 2015
    I don't think it should be there. My guess is that someone has created that schematic by reverse-engineering a circuit, but has not done so accurately. I see no reason why low secondary voltages would need to be referenced to the high voltage line. It looks potentially lethal.
     
  15. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Ok after further reserch i can see that the above diagram is different (probably for a different model pcb). Here is one i found that checks with the PCB wiring.

    on the upper left corner is the diagram of the PSU. I also see that the mains Line is connected with pins 1,2,7,8 of the LNK304PN switch and with the transformer's secondary winding and output capacitors positive side, so the first diagram is correct in that part.

    As far as i can tell the 330uf Capacitor is the -12V output and i assume the 1000Uf capacitors are the -5V output.

    Maybe now can shed some light on my darkness.
     

    Attached Files:

    Last edited: Feb 14, 2016
  16. Alec_t

    Alec_t

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    754
    Jul 7, 2015
    So much for my theory ;). In the latest schematic I make TP48 = -12V and TP29 = Vcc = Phase = +xV (+5V?), both voltages referenced to TP31 = GND (common). So GND is floating xV below Phase. I don't see any -5V supply?
     
  17. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Tp31 may be reference point indeed. though i am not sure this black symbol is (common) symbol.

    why do you think vcc is +5V? what is Vx ? i assume it is -5V judging from capacitors polarity.
     
  18. Alec_t

    Alec_t

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    Jul 7, 2015
    It's marked 'GND'.
    xV is an unknown quantity. Where do you get "5" from? It most likely is 5, because it's the supply voltage to the micro.
    The capacitor polarity indicates that Vcc is +ve with respect to GND.
     
  19. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Yes you are correct on both. It is a bit hard to read this schematic with such low resolution.

    I dont understand how Vcc is 5 volts while the winding is connected to Mains line.

    I understand the circuit from mains, varistor, filter caps, switc, and transformer's primary. I also understand the feedback loop for the switch but the circuit on the secondary side i do not understand.
     
  20. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    .


    Sir HellasTechn . . . . . .



    Well . . . .in further contributing to your info pool . . . this is supposed to be the manufacturers schematic for your boards power supply, I have the whole boards schematic if further needed.

    [​IMG]


    That power supply failure must be a common problem, as they actually offer repair kits for the power supply section within that pricey whole board . . . but . . . of course, its NOT including your very SPECIAL part.

    http://www.ebay.com/itm/Repair-KIT-...3-L1782-L1790-L1799-L2158-L2524-/191737116960

    I will let the commons neutrals and the HOT AC lines be sorted out by you . . . . You-are-a -peans . . . . . but I don't think that is being a shock hazard problem, since that whole board is being TOTALLY and COMPLETELY sealed within in a heavy plastic cover / case.

    [​IMG]

    Now that units schematic referencing, is being very weird in its polarity assignments, seeming like the person who drew it had never seen another schematic to compare and work from, for incorporating industry standard, common, repetitive and uniform procedures.
    I just treat reading it like the early days of transistors, where they used a WHOLE LOT of PNP germanium transistors, where + was used as your common ground and you would thereby see a whole lot of +'s going to the common ground and -'s going to the collectors of transistors. You just have to think backwards from the norm.


    Below is shown a particular Whirlpools power board section that "blew" on the primary side, as you can see by the heated choke between the primary filter caps for the raw DC supply, along with the pulled power IC..


    (Clickee-clickee on, to . . . . . .makee . . . . . . BIGGIE-BIGGIE)

    [​IMG]



    I see that there is a board available from Phoenix USA . . . .wherein a repairman bought a new board and that did not fix the machine . . . and then, he did the common car "mechanic" technique of replacing
    every other possibly suspected part until it was finally fixed . . . . . and then he made out the bill.
    Anyhow, the used board is for sale for $20 as of the 19th of Jan 2016.
    It is a Cabrio, vice Domino but the internal power supply parts are probably being the same.

    http://phoenix.craigslist.org/wvl/sop/5410480668.html


    Thasssit . . . . .


    73's de Edd


    .
     
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