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Dell SFF 760 blinking 3, but PSU

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    Dell SFF 760 blinking 3, but PSU

    Several days ago one Dell 760 came to me. Not turning all at all, they said that before this for some time sometimes it turned on fine and then refused or just restarted sometimes without user intervention.
    The diagnostic lights on the front panel - blinking digit 3. After some testing and removing the CMOS battery, I had orange blinking power button - just one time and then back to blinking digit 3.
    3 if you look at the diagnostic lights description is connected with the CPU.
    The BIST test on the CPU ran just fine. BIST is a feature of DELL PSU-s, which initializes power supply test. Fans spinning, HDD spinning - everything seemed ok with the PSU. So, Dell technician will probably say that this is Mobo problem and will offer expensive repair. They will refuse to disassemble the PSU.
    Well, in fact I am DELL and HP certified. But... Neither the error code nor the BIST were correct. When I opened the PSU, I saw 10 bulging Lelon caps - all 2200 uf and all failed. And one 100uf cap bulging between the transf and some radiators of other components. It was extreme PITA to replace the caps without complete disassembly of the board assembly. They have one main board, on which there are 4 boards using soldered pin connectors and rotated 90 degrees of the main board.
    I had no spare PSU, because the PSU uses nonstandard power connector, not the normal ATX power connector like some decent SFF PC-s.
    It was a PSU problem. Because of the caps, the PSU provided out of spec power to the mobo. Even if the BIST ran just fine and voltages were okay, measured with multimeter. I did not have my portable oscilloscope with me to check the quality of the provided power, not just the voltages.
    Always suspect the PSU first in this SSF systems and always take it apart to check for caps and anything suspicious.
    Now the system works and works stable. I uses Sancon 105C caps. And when there is 16V, I like to use 25V. Where there is 25V, I like to use 35V.
    Useful conversions. I don't "speak" imperial. Please use metric, if you want to address me.
    1km=1000m=100000cm, 1inch=2.54cm, 1mile=1609.344meters, 1ft=30.48cm 1gal(US)=3.785liters, 1lb=453grams, 1oz=28.34grams

    #2
    Re: Dell SFF 760 blinking 3, but PSU

    interesting. I looked at the motherboard online and it looks like a regular 24 pin adapter, but yeah, sometimes the key is different on several pins

    here is a pinout of Dell ATX connectors
    Attached Files
    Cap Datasheet Depot: http://www.paullinebarger.net/DS/
    ^If you have datasheets not listed PM me

    Comment


      #3
      Re: Dell SFF 760 blinking 3, but PSU

      Dell uses 24pin mini connector, not the standard ATX. And even if you find that small PSU, but with standard ATX connector, you will have to use adapter or cut the connector and solder the DELL mini connector.
      Last edited by televizora; 05-02-2021, 11:41 AM.
      Useful conversions. I don't "speak" imperial. Please use metric, if you want to address me.
      1km=1000m=100000cm, 1inch=2.54cm, 1mile=1609.344meters, 1ft=30.48cm 1gal(US)=3.785liters, 1lb=453grams, 1oz=28.34grams

      Comment


        #4
        Re: Dell SFF 760 blinking 3, but PSU

        Recap this, please. Photo attached. This PSU is complete nightmare.
        The engineers, who designed it should burn in hell.
        3 separate boards on soldered pin connectors, 90 degrees from the main board.
        To get to 2 of the caps, you have to unsolder 15 pin row connector.
        All 2200uF LTEC caps blown. One 100uF Ltec between the two transformers also blown.
        Not only this, but half of the PSU is glued using hot silicone glue.
        You have to first cut the glue while trying not to damage something and then unsolder the board, which on the photo is removed.
        It's place is in the middle, you can see the holes for the pin row connector on the main board.
        Attached Files
        Last edited by televizora; 05-07-2021, 02:52 AM.
        Useful conversions. I don't "speak" imperial. Please use metric, if you want to address me.
        1km=1000m=100000cm, 1inch=2.54cm, 1mile=1609.344meters, 1ft=30.48cm 1gal(US)=3.785liters, 1lb=453grams, 1oz=28.34grams

        Comment


          #5
          Re: Dell SFF 760 blinking 3, but PSU

          Nice to hear you got the power supply going!

          BTW, how old is the power supply? Looks relatively new-ish... though Optiplex 760 SFF I guess means at least around 10 years old. That's more or less inline with when these Ltec c[r]aps are expected to fail. IMHO, Ltec are probably the worst in these OEM PSUs. Samxon GF and Taicon tend to hold usually a little longer. Teapo might also... though they are a bit more hit and miss.

          All in all, nothing new here. Both Delta, HiPro (Chicony), and LiteOn use Ltec, so gotta watch out really in any of the OEM PSUs. Otherwise, though, they are pretty solid PSUs. (The newer ones, however, have APFC circuit, and that's another can of worms for down the road when it roasts is primary cap... at which point, the PSU probably won't be worth repairing... or maybe it will, given these are SFF PSUs and replacements aren't exactly cheap - especially if ATX pinout is non-standard.)

          Comment

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