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    Help needed to revive a blown power supply

    Hi all,
    Got a used working computer running Windows 7 about 3 months ago. Two days ago, the power supply blew up with loud spark and i immediately shut off the power. It was an unknown brand Tatu (output 450 w).
    Upon opening, i found out the two transistors on heat sink 1are fried with burn mark. Replaced the two trans(E13007 type). Also checked if the surrounding components are affected. The diode seems to be working, i pulled one leg off and tested using diode test. One side got reading while swapping test probe shows 1(infinite).
    I also pulled out the nearest 2 small caps at C5 and C6, they are both 10uf50v. Capacitance read 10.5 to 11.2 uf while esr from 0.46 to 0.5 (based on these reading, i soldered them back on board).
    Later, i pulled the 2nd heat sink out, tested those rectifiers by diode test. Black probe on middle leg while red probe on left and right leg got some reading. From the readings, i guess those rectifiers are still good.
    Tested the 16 pin(SDC 7500 voltage pwm),dc test with black probe on pin 7 and red probe on pin 12 shows 15vdc, at pin 14 it shows 5vdc.
    Tested the 14 pin (SDP 339 voltage quad comparator), dc test with black probe on pin 12 and red probe on pin 3 shows 5vdc.
    For testing this blown power supply, i replace the fuse with a series lamp bulb. Upon switched on power, the bulb lighted for 1 second then no more light. So there is no short. But the output power on the 24 pin still not appearing. Only the 5vdc standby power is detected from the green wire. Any help to revive this psu is greatly appreciated.
    Attached Files

    #2
    Re: Help needed to revive a blown power supply

    When you switch on the PSU with the green PS-on wire to ground you also need to provide a minimum load in many cases.
    An old hard drive that you do not care about can for example act like a minimum load for the power supply.
    "The one who says it cannot be done should never interrupt the one who is doing it."

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      #3
      Re: Help needed to revive a blown power supply

      Realistically, those MJE13007 clones, the size of the main transformer, the wimpy heatsinks, and not very large output inductors mean the realistic maximum continuous output power is in the 200W-25oW range. Note also that the 12V and 5V rectifiers are both rated for less than the label currents, and the 3.3V label and rectifier ratings are equal.

      I realize the system had been running for some time with this PSU, so those factors would mainly be relevant if you hope to expand the system.
      PeteS in CA

      Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
      ****************************
      To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
      ****************************

      Comment


        #4
        Re: Help needed to revive a blown power supply

        This is a very sad-looking PSU. Probably candidate for this thread, but digress. I don't suggest to repair it for use in a computer, as it's just very anemic. However, if you do want to repair it for learning purposes, these cheap PSUs are fairly straight-forward (well, I say that after going through a similar rodeo and struggling with one for quite a bit.)

        That said, probably start by reading this thread:
        https://www.badcaps.net/forum/showth...light=kdmpower

        In particular, read these two posts in detail:
        https://www.badcaps.net/forum/showpo...00&postcount=8
        https://www.badcaps.net/forum/showpo...1&postcount=11
        https://www.badcaps.net/forum/showpo...3&postcount=12

        TL;DR: check the driver transistors (typically 2SC945 or equivalent) and surrounding diodes on the secondary side that drive the middle transformer (which drives the 13007/13009 BJTs on the primary.) See this schematic as a reference:
        https://www.badcaps.net/forum/attach...6&d=1608943994
        Your PSU may not look exactly the same, but it should be similar. This is just the driving circuit for the main PS. In my case, one of the diodes in front of Q8/Q9 was partially-shorted, and it gave me a good run-around until I found it. So check the driving circuitry and also for any open resistors in that circuit.
        Last edited by momaka; 03-17-2022, 02:27 PM.

        Comment


          #5
          Re: Help needed to revive a blown power supply

          I had used an old hard drive as load but the psu still not working as it should. Also read through the given threads and they are helpful. Since i spent quite an amount of hours without success, i think i will keep this psu aside. Maybe some of the parts will be useful for other project.
          Anyway, thank you for all the tips and assistance.

          Comment


            #6
            Re: Help needed to revive a blown power supply

            normally when these type of PSU blow, you have to measure the resistors around it also. I make a close up look, your resistors seems to be gone.

            Comment


              #7
              Re: Help needed to revive a blown power supply

              Originally posted by anikin73 View Post
              normally when these type of PSU blow, you have to measure the resistors around it also. I make a close up look, your resistors seems to be gone.
              Those resistor near bjt13007 are at R8 (1ohm), R5(1ohm) and R6(2.7k ohm). R6 is open and i replace it with 6.8k ohm resistor from my stock.
              Will replacing with a higher ohm resistor affect the psu power on?

              I am trying to repair this old psu for learning purpose and not to use on computer or anything critical. Fyi, the two big main cap is 470uf 200v type. Upon power on, i tested it and dmm showed dc reading of 158v on each of the cap. Our ac main is 230v type.
              The psu output 5vdc standby and no other output. The fan not moving a bit. I replaced all the small caps at c6,c5,c24 and c22 to 10uf 50v type and the 5v standby still remains and no other output. Any suggestions?

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