Need input from power supply/motherboard guru ..

By timoteo
Nov 13, 2010
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  1. HI:

    I have and "old" (ok, it IS old) Micron Millennia XS (1.7ghz P4) tower desktop. It has been working fine for years (left on continuously), but recently has been found shut off with it power light red instead of green. (Which normally indicates sleep mode.) It stays on anywhere from 2 hours to more than 12 hours. I've never caught it shutting off, so I can't swear it isn't going into sleep mode, but I can't get it to power up without unplugging the unit and plugging it back in and then restarting. (BTW, some power was definitely getting to the mainboard, as the small green LED on the mainboard was lit inside the computer.)

    Anyway, I deduced it had to be: a) An OS issue (ruled out now), b) Heat Issue, or c) a Power Supply Issue.

    Having rule out the OS issue, and seriously doubting a heat issue, I decided to try the PS issue (besides it's the easiest to test vs. the heat issue.) So, I went to use a PS from my even older Micron P3 700mhz that was not being used, however it did not have what appeared to be the right connectors, so I grabbed a PS out of a "newer" Dell XPS 3.0ghz P4 I wasn't really using. Here is where it gets weird ...

    I go to pull out the PS from the Meillenia XS and discover it has the normal 20-pin mainboard connector, but ALSO a 6-pin (auxilliary connector one RED, two ORANGE, three BLACK, labeled "P8"). Now the motherboard also has the standard 4-pin +12v2 connector (two-yellow two-black wires)as well. However, it seems like there was nothing plugged into it, but from my understanding it had to have been or the CPU would not get enough power (or possibly any power). The old power supply does have the +12v2 4-pin connector (and of course the aforementioned 6-pin aux.). The newer PS (from the DELL) does not have the 6-pin connector.

    So, sorry for the long drawn-out setup, but I guess what I want to know is ... will plugging in the 4-pin +12v2 connector (which I'm pretty sure had to have been connected before) and not having an auxillary (6-pin) connection cause any problems. The motherboard is a D850GB chipset if that helps.

    Also, IF for some reason that 4-pin +12V2 connector had come out ... would my PC have even powered up, and if so, could that have been the cause of the computer randomly shutting off, and therefore my old PS was fine?

    Thanks, and again, apologies for the lack of brevity.


    PS> Is this some kind of hybrid AT/ATX motherboard or something?
  2. captaincranky

    captaincranky TechSpot Addict Posts: 11,467   +1,760

    First, I believe that Intel chipset 850 is the immediate precursor to the 8X5 chipsets, with Northwood P-4 CPUs, (845,865, ya da ya da yadda). However, I've seen references to an older socket, (423), as well as the socket 478, with 850 boards.

    (Edit; I just researched this. It seems there is an adapter to allow the use of socket 478 CPUs in the 850 boards, which are socket 423).

    PSU failure is very often accompanied by a failure to wake up from standby. The seem to run OK, but when you shut them down, the seem to "die of natural causes".

    The, "you gotta pull the plug, and plug it back in before it will start" behaviour shows a failure in the "soft off" circuit.

    I think there's an amount of +5 volt current required on standby. This is to keep USB "alive".

    Before I would plug the 6 pin "aux" connector into anything, I would check the voltages. The red should be =5 volts, and the 2 orange wires MUST be 12 volts. The 3 blacks are grounds, keyed to the hot wires.

    In a rhetorical sense, if the 6 pin block would plug in correctly, with the two orange wires to the 4 pin CPU block, (and they were in fact +12 volts), it would probably be fine.(Don't forget proper orientation, the positive terminals should be marked on the board).

    In the real world sense, I'd definitely spring for another PSU, and not experiment with it.

    I don't think the +12 supply directly to the CPU back then, was as critical as it is today. Once upon a time, CPUs had a much lower current requirement. (Which is why they also ran cooler).

    All of that said, I seriously doubt that your old PSU was fine.
  3. timoteo

    timoteo TS Rookie Topic Starter

    Thanks for the reply, Capn'!

    I'm almost positive it is indeed a socket 478. Wouldn't bet my kids soul's or anything on it, but am pretty sure. But anyway, on to more relevant things (I think) ...

    The whole waking up from Standby thing makes sense if I had it going into standby, but that was one of the first thing I did was to make sure everything was disabled both in Windows and in the BIOS. I never caught it powering off, so I'd need to set up a timelapse capture or something to be sure, but I think it had to have been just powering off, no standby. I'm really wondering if the 4-pin +12V2 connector WAS plugged into the MB originally, and when I was in there recently I unplugged it or something accidentally or otherwise, and this was causing the random shutdowns?

    Well (and sorry if my long-winded tale made it confusing) actually, the six-pin auxilliary power has always been plugged in ... into a six-pin receptor on the MB. (That's why I thought this MB was some kind of hybrid.) The connector came with the original PSU. My question was whether or not with the "new" PSU not having one, if it would make a difference?

    Could be, although I question it now that I discovered that it had a 4-pin 12v2 plug and the MB has a 12v2 receptor. Really makes me wonder if that came undone.

    Guess I'll try out the "new" PSU sans 6-pin, plug it's 4-pin in (which should be fine/great as far as the CPU is concerned) and see what how it handles. Not sure what exactly the 6-pin auxillary power provided for, but I guess I find out if DVD or HD drives are not working or something. My GUESS is it's redundant power, but we'll see.


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