PC power supply: failed in weird way

Discussion in 'General Electronics Chat' started by jeka616, Nov 4, 2011.

  1. ashokcp

    Active Member

    Mar 8, 2007
    50
    2
    There are cheaper power supplies with no MOV, Y-CAPs, CM / DM Chokes, while there are footprints in the PCB for these components. There are jumpers for CM/DM chokes!
     
  2. Adjuster

    Late Member

    Dec 26, 2010
    2,147
    303
    A cheap and basic supply is one thing: it may do an adequate job for a reasonable length of time, particularly if not pushed to the limits if its claimed specification.

    A faked copy made without important safety features is another matter altogether. It is not hard to imagine such a contraption destroying whatever it is connected to, as well as resulting in possible fire or shock hazards.

    The present apparent free-for-all in China really has me worried. Apparently there is not an established culture of respecting UL listing, CE marking etc, so bogus equipment may be sold as meeting these requirements. Caveat emptor, as they say, but how in heaven's name is the ordinary punter supposed to know the difference?
     
  3. sheldons

    Well-Known Member

    Oct 26, 2011
    613
    102
    i always treat these power supplys the same....i have been in the trade now for some 20 years now ,repairing crt,pc ,plasma and lcd(plus the various audio stuff that comes my way )and these smps are if anything a bit better designed than say certain lcds and plasmas(no makes mentioned) but ive had many a happy hour repairing these things after people have connected them in all sorts of weired and wonderful ways.just to purely make the point that his power supply for what ever reason has failed is easily repairable,and if given a photo or type nr could perhaps find some service info out for it.
     
  4. sheldons

    Well-Known Member

    Oct 26, 2011
    613
    102
    buttttttttt........just an example........ive had this quite a few times theres a certain 42 inch lcd tv by a certain manufacturer which comes in to the workshop with the fault comes on-but straight into standby with either no leds on or flashing leds....upon examination incorrect parts have been fitted to the board which over time have overheated and in some cases quite dramatically failed(electrolytics with too low a working voltage-and generally sub standard cheap parts used)and quite amazingly these components are part of the feedback network for the powersupply with the result that as they fail(wether they go hi esr etc)voltages increase which eventually cause failures elsewhere.....ive had some pc powersupplies with the same problem over the years...also as they are enclosed and there is quite a lot of heat generated some manufacturers tend to fit cheap parts(not hi temp parts)which just dry out and cause problems.had one the other week which when it failed scrapped the rest of the pc too....
     
  5. Adjuster

    Late Member

    Dec 26, 2010
    2,147
    303
    It is interesting to hear that you are in the business of repairing such things. Are you really under the impression that computer SMPS do not achieve mains isolation, as your earlier post would seem to imply? If so, you might pass as acceptable a supply which has actually suffered an insulation failure. In the worst case, this could have fatal consequences.

    I can see a particular danger of this if for your own safety you habitually power devices under test from an isolating transformer, a wise precaution particularly when dealing with supplies which may genuinely be non-isolating, e.g as used for CFLs.

    Mercifully in most cases the connection of such a faulty computer supply to a grounded outlet would prevent a serious accident, but this should not be relied upon.
     
  6. sheldons

    Well-Known Member

    Oct 26, 2011
    613
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    no not at all all items have to be repaired to a set standard,most pc powersupplys are quite adequate in that respect but the same rules for repairing this type of supply and an ordinary say lcd or crt power supply still apply from a safety point of view.i still use my variac when working with these as when you can slowly increase the supply on test after a repair it does sometimes save a bit of time if theres still a problem during a repair
     
  7. thatoneguy

    Expert

    Feb 19, 2009
    6,349
    732
    I've had 2 PSUs die. Two different well known brands for being solid.

    Both of them served me well for years. Both of them died when I upgraded my video card to within 50 Watts of their max output.

    The worse part: Both of them died in a way as to take out the motherboard/processor/memory with them, though the video cards survived.

    I've written it down to the computer gaming gods telling me that if I want nice graphics, get a new faster system, and make the spare a linux box. :D

    (Current Supply is Thermaltake 1000W -ish (1100?), w/nvidia 485 GTX video)
     
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