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-12V-less HP server unit: does majority of current boards even require the rail?

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    -12V-less HP server unit: does majority of current boards even require the rail?

    I acquired few HP HSTNS-PF01 units from Flextronics (506077-002, spare 506247-002) and noticed they do not even carry -12V rail any longer. Do some of the modern boards actually require it to start? I have to admit I have not looked after this before, but since there is virtually nothing which needs it anymore, I believe most boards maybe do not even check for the presence of the voltage…?

    Than second quiestion, there are Samxons GK on the secondary, some D8, some D10, some D12.5. Is it even worth replacing? I do not think I ever saw any bad caps in any server unit (not even in the failed units) no matter if it was some Ltec or similar crap and after many years of continuous use.

    While I can replace the caps, the units are not so complicated to remove the boards, it is not that easy either, and when there is 95% chance (ya remember Fallout? ) that when they'll fail, it will be because of something else…is it even worth the effort? I got multiple of these units…and it is also possible Samxon has improved the series in time, or they at least keep better quality control for customers like Flextronics…
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    #2
    Re: -12V-less HP server unit: does majority of current boards even require the rail?

    I don't know, but as long as the board does not have an ancient Super I/O chip I think it might be ok.
    Those are quite common even on modern ~ish boards (That lack ISA & COM ports, which would require the -12v)
    "The one who says it cannot be done should never interrupt the one who is doing it."

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      #3
      Re: -12V-less HP server unit: does majority of current boards even require the rail?

      they wouldnt need it for com ports if they use modern charge-pump'd buffers like in set-top boxes etc.

      the other thing it used to be for was the negative side in the audio section.

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        #4
        Re: -12V-less HP server unit: does majority of current boards even require the rail?

        Yeah but all the cheap integrated Realtek's do not provide much power - what for anyway - they provide enough for small headphones and everything else has its own amplifier built-in. Checked the datasheet of ALC882, they draw +3.3 and +5 V, one of few devices to actually draw even from these rails (so group topologies have some minimum load).
        Last edited by Behemot; 12-23-2017, 10:00 AM.
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          #5
          Re: -12V-less HP server unit: does majority of current boards even require the rail?

          PCI slots have a -12V contact while PCI Express slots do not have any connection to -12V.
          From what I know, older PCI serial port and older PCI network cards require -12V; later PCI serial port cards dispense with -12V (in my belief) since they typically use RS-232 transceivers with inbuilt negative voltage generation, and the same would go (again, in my belief) for later motherboards with serial ports onboard, although -12V might be required for certain PCI and onboard sound cards (mainly older units).
          My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.

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            #6
            Re: -12V-less HP server unit: does majority of current boards even require the rail?

            Some newer boards no longer carry PCI so that wold likely mean they really do not need -12 V I guess. I am finally returning to Prague 2day so I'll start testing it
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              #7
              Re: -12V-less HP server unit: does majority of current boards even require the rail?

              Originally posted by japlytic View Post
              PCI slots have a -12V contact
              Thanks! That cleared up something for me:
              Was wondering why a HP Compaq 8000 Elite PSU that was posted about on Junnyguru had -12v, yet it lacked 3.3v, 5v and used 12vsb instead of 5vsb:
              Turns out it has regular PCI slots so that's why they could not get rid of that voltage rail.
              "The one who says it cannot be done should never interrupt the one who is doing it."

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                #8
                Re: -12V-less HP server unit: does majority of current boards even require the rail?

                PCI relies heavily on +3.3 V IIRC. Most likely the other rails are DC-DC'ed somewhere else, it was just easier to make -12V directly in the PSU especially if they did not require very tight regulation.
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                  #9
                  Re: -12V-less HP server unit: does majority of current boards even require the rail?

                  Yes that is true, they could have used -12v regulators on the mainboard too.
                  "The one who says it cannot be done should never interrupt the one who is doing it."

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                    #10
                    Re: -12V-less HP server unit: does majority of current boards even require the rail?

                    A board from HP ProLiant ML110 G6 POSTs fine. MSI Z68A-G43 (G3) only twists fan and the unit shuts down and does not power on again input until power is cycled.
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                      #11
                      Re: -12V-less HP server unit: does majority of current boards even require the rail?

                      Intel DZ77SL50K POSTs fine.
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                        #12
                        Re: -12V-less HP server unit: does majority of current boards even require the rail?

                        You can make a small circuit with a MC34063 switching regulator, or with a voltage doubler/inverter to create -12v from 12v ... you only need a few mA since pretty much nothing uses -12v these days.


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                          #13
                          Re: -12V-less HP server unit: does majority of current boards even require the rail?

                          I know there are al-in-one regulators, but I just wonder whether it is worth it - seems that there are many boards to choose from which don't need it
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                            #14
                            Re: -12V-less HP server unit: does majority of current boards even require the rail?

                            Intel DQ57TM also works.
                            Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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