power supply defective

Discussion in 'Homework Help' started by penampar, Jul 17, 2007.

  1. penampar

    Thread Starter New Member

    Apr 22, 2007

    I got one DVD player and got power problem... here the picture [​IMG]

    1st the fuses is good.. 2st i tried discharge current from the big capacitor and i found it doesn't work... i just finish replace that capacitor and test the dvd player.. this time still not work.. 3rd i measuring dc volt at the big capacitor and i get[​IMG] 331 volt... finally i tried measure dc output to the dvd board, the whole output doesn't give and volt i only received mV...[​IMG]

    so anybody can help me what part has defective??

  2. techroomt

    Senior Member

    May 19, 2004
    penampar, i'll tell you what i'd do, in order, until i find the problem.

    1. visually inspect board for obvious problems (overheating, connections etc.)

    2. static (ohm) test - fuses, transistors (u1), diodes, resistors, caps - may have to remove som from circuit to completely verify integrity.

    3. dynamic (voltage) test - follow voltage through the card. you must know what components do in a circuit here.
    good luck!
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    That seems to be a switch mode power supply. Check the voltage after the transformer and before it. Also check if the current is being switched before the transformer. A normal signal should have pulses with a frequency of about 500Hz to 5KHz.
  4. mrmeval

    AAC Fanatic!

    Jun 30, 2006
    check the blue resistor. If your meter has diode check use on the diodes, if they check bad unsolder one leg and test agiain. Find a data sheet for the IC so you can measure voltages. If you don't have a scope you may need one. (use an isolation transformer!!!). Use the scope to look for wave forms based on the datasheet.
  5. Gadget

    Distinguished Member

    Jan 10, 2006
    I have found in my experiance, that if no fuses or protection resistors in the primary have blown, then the semiconductors in the primary are probably OK. Many SMP faults tend to be leaky or low electrolytic capacitors. Take special note of any lower value high voltage units in the primary. There is normally a resistor voltage divider network in the primary that can also give probs.
    Check for any bulged or leaking capacitors in the secondary.... even just replacing them all on spec.

    BTW, your photos are coming up so tiny that I can barely make out its a PSU.