12v rail low for shuttle power supply

please help me for this problem...i have shuttle pc which the power supply doesn't work..i try to check the dc ouput and i found out that 12v rail it seems has a low output... only reads 8 to 10v..i check all the caps it looks fine.i also take out from the pcba all the caps and tested good..i dont if the schotty diode or the mosfet it causing the problem but i dont know what the proper test of this mosfet and schotty diode on circuit board..anyone who got an idea please help me what next should i check?..thank you very much..

Brgds,
Joseph
11 answers Last reply
More about rail shuttle power supply
  1. It's probably the mosfets if the voltage is that low, as far as how to test the mosfet, try this:

    http://www.4qdtec.com/mostest.html
  2. sk1939 thank you for your speedy reply...i will try to test the mosfet using your method today and i will update you the outcome...thank you...
  3. Their power supplies were never great especially the older ones. Looks like you might have to rebuild the unit or hunt down a replacement. Good luck testing the mosfets and diodes searching for the fault. I am sure that there must be one dead mosfet or diode. Also check the chokes.
  4. thank you for you help and idea nforce4max...it looks ok the mosfet as i checked today...what makes the mosfets drain down the 12v voltage dc ouput?i try to replaced 2 caps with 2200uf/ 25v to 1000uf/ 50v..do you know what is the effect or affect to replace with lower capacitance?is the ouput will lower or higher voltage? with lower capacitance will affected the ouput?i dont think the schooty diode will cause of it..cause the 3.3v ,5v ouput is ok..is only the 12 volts ouput is low..no idea really..please help...to check schottky diode is the same with normal diode?..or you can check with meter ohms seetings isnt it?can i check the schottky diode on circuits?if you have schematic diagram of shuttle power supply to shared with me, i appreciated..love to see that diagram..at the moment i am blindfolded conducting the repaired of my power supply no diagram at all...thank you all..for all your help..

    brgds,
    jojie
  5. It is best to replace caps with the same voltage but the uf rating can be higher or lower but be sure that the caps are rated 100c+. As for the diodes and mostfets look for guides posted online how to test them properly.
  6. It is best to replace caps with the same voltage but the uf rating can be higher or lower but be sure that the caps are rated 100c+. As for the diodes and mostfets look for guides posted online how to test them properly.[/qu


    hi nforce4max, thank you very much...what do you mean by 100c+?
  7. That is temp rating. Low quality caps can't take much heat so most are rated for 85c but some still get labeled for 105c. Look on youtube there are some guides explaining how caps work and the differences.
  8. nforce4max said:
    That is temp rating. Low quality caps can't take much heat so most are rated for 85c but some still get labeled for 105c. Look on youtube there are some guides explaining how caps work and the differences.


    hi ok thanks....i will see it now...
  9. hi guys, needed your help again...anymore idea's...my shuttle switch power supply still not working...i am desperate to fixed these culprit as i already spend a lot of time just to sorted out these power supply problems..

    these are all i done at this point, replaced the caps, still not working,checked mosfets it seems ok..schottky diode not sure...what do you think guys?i measured the diode looks ok..any idea how to measured schottky diode on board? check the using multimeter with diode testing setting..it seems ok...what else should i check?i think you guys are more experienced to troubleshoot this kind of problem..thank you very much..please help me..

    brgds,
    jojie
  10. step 1 - replace power supply with a decent brand one

    step 2 - refer to step one.

    seriously, you could waste much time trying to fix a power supply, unless there is something obviously wrong with it (bulging caps/dry joints). If you want to take it further you need access to the schematics and an oscilloscope.
  11. iam2thecrowe said:
    step 1 - replace power supply with a decent brand one

    step 2 - refer to step one.

    seriously, you could waste much time trying to fix a power supply, unless there is something obviously wrong with it (bulging caps/dry joints). If you want to take it further you need access to the schematics and an oscilloscope.



    thanks...i have oscilloscope at work mate...the only problem i cant get schematic diagram online with shittle power supply model..if anyone of you has one..please shared with me..thanks
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