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Thread: 5v Line reaches new lows.

  1. #1
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    5v Line reaches new lows.



    I'll let the image speak for itself:



    A while back it was at 4.73v, then 4.65v and now 4.52v. This SL350 has been problematic in the past (ATX connector contact loosened, causing spontaneous reboots) and I'm getting some funny effects from this low 5v. First, the ATX connector is browning in some 5v contacts (due to higher amperage I believe) and the memory needs more conservative timings to operate reliably.

    I've been considering wiring the P4 5v connector to three mosfets on the mobo. It's an 8KHA+... would the ones on the topside of the board be the correct candidates?

    This PSU has no pots in it and no one I've asked knows how to artificially elevate the rails in it. Being on a transformed mains source may have something to do with it ( ), but I think ultimately this XP1800+ @ 2400+ is drawing too much power for this PSU and in the long run I'll need to replace it with a beefier model.

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    Ultimate Member rraehal's Avatar
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    I agree with you about beefing up the power supply. Do not get a cheap one. Antec seems to work well and many people here have recommended that brand.

    Your O/Ced rig may be cause the existing powersupply to have problems. Cheap supplies have poor quality components. The usually are rated at +/- 5% which can explain your voltage loss.
    -- Mathias

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    The thing is, it is an Antec power supply, model SL350, SmartPower series. To be quite honest I'm not that impressed with it -- this system isn't exactly a duallie rig running five 15k SCSI drives. The CPU is consuming about 85W of power and the motherboard copes with it somehow, I guess. Still, being 350W, and allowing for 35A on the 5v rail it should be ok.

    Another system has the Truepower 550W - 40A on the 5v rail - with a much more power-hungry athlon @ 2.33GHz with an R9700 pro and the nforce2 chipset. Even though it's expensive, it hasn't let me down - yet.

    I think I'm settling for the Sparkle/Forton 430W. All Truepower models under 550w (true480, true400) have failed to impress me - often the 5v rail drops to 4.7.

  4. #4
    Senior Member lptech's Avatar
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    causticVapor-

    I think that you are in need of a PSU (Power Supply Unit) that could deliver very tight regulation on the output with minimal ripple! I don't know if you are able to get US made power supplies there but I would recommend the Turbo Cool line of PSUs to you from PC Power & Cooling Inc. The Turbo Cool line is the best period.

    Here's a link to their website:

    http://www.pcpowercooling.com

    I've personally used their Turbo Cool line of PSUs and have never been disappointed by their performance! Yes, they are more expensive but as the saying goes, "you get what you paid for."
    One of my machines is over five years old and still runs solid using their power supply! I've seen too many power supplies go bad or have an early death and the reason that they do is poor design and cheap components! That is why, whenever I build something that is mission critical, I use the Turbo Cool line of PSUs from PC Power & Cooling Inc.

    Here's another link from THG:

    http://www6.tomshardware.com/howto/20021021/index.html

    I think that it gives a better idea of how some power supplies fail at delivering their stated output capability. Quality control is the key when you go out and purchase power supplies! Unfortunately, many manufacturers are looking at profits in the short term and not the long term of getting customer loyalty. Many of us are victims of these companies' lack of commitment to the customer. So, "Buyer Beware!"

    lptech

  5. #5
    Member 2penguins's Avatar
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    Yep, get yourself a Sparkle or Aopen...at least they have trim pots.

    My Aopen 400 watt voltages were also dropping (a brand new PSU) I had to open it up and adjust the 5 & 12 Volts It's set stable ever since.

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    Wow, true indication of high CPU power consumption, dropping 5v rail and surging 12v rail. My +5v is now at 4.44v and +12v is at 12.3-12.4v.

    Lots of amperage going through that ATX connector, no doubt

    New PSU time on the double

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    What r u using to monitor the voltages? The picture isn't coming up for me right now... But if those are accurate, I agree... Definatly time for a new PSU... I have heard really good things about the pcpower&cooling PSU's, although I haven't had any personal expierence with them. I've been very pleased with my Enermax. Its a 350watter and I've got a 2100+@2700+ (1.775 vcore) 768MB PC2700 DDR @ 2.8volts, EPoX 8K3A+ board, Ti4400 @ 285/600, 6 case fans (2 neon/not including the two on the PSU), 7200 RPM drive, DVD, CDRW, neon tube, and all 6 PCI slots are full. Ran Prime95 for over 12hours with no errors, and its constantly at 100% load 24/7 crunching UD. Not sure how close I am to the PSU's limit, but my HD is starting to fill up, so I may need to add another soon, but I don't foresee any issues. Definatly get that PSU changed out before you start frying components by running too much current through them.

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    Yep, PC Power&Cooling, Sparkle, Fortron, Aopen, Antec true550.

    Will obtain one of those -- temporarily running a 300W antec backup PSU. The 5v rail is now at 4.83V, which is good. Unfortunately my multimiter's broken so I didn't get to measure the connector.

    Either the SL350 is failing or there is a load of impedance due to dirtied contacts (loosened up quite a bit.)

  9. #9
    Member 2penguins's Avatar
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    Have you noticed that motherboard manufacturers won't tell you how their boards make the power they use?

    I've read a few things that say the CPU current is made from the 12vdc line, if that were true then the 12 volt line would max out the load capacity of the ATX plug once the CPU pulled 72 watts.

    I haven't tested mine, but a friend tested the amps on an Asus A7V and the 12volt line was not being used to make power for the CPU, it had to be the 5 volt lines.

    It is posible that you had one weak connection on one of the 5volt wires and it caused the rest to overload.


    I've heard of this sort of thing happening alot.

    Makes me think it would be a good idea to look for a PSU that comes with a 9amp ATX plug instead of the standard 6amp plug.


    I just wish that motherboard makers would let us have a bit more information, it would sure help in running down power supply problems.

  10. #10
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    Deriving vcore from the 12v rail is smarter because less amperage is required to supply the same amount of power.

    I believe only boards that use the square 12v plug actually derive the CPU voltage from the 12v rail. I may be mistaken, however, as the power regulators could be (internally) designed to allow for 12v conversion directly from the ATX connector.

    "It is posible that you had one weak connection on one of the 5volt wires and it caused the rest to overload. "

    I do agree that the dirtied connector probably increased the resistance, and caused overheating on the 5v rail and overloading on the 12v rail.

    I also agree with the separate connectors for CPU voltages - they do allow for a shorter path with fewer junctions, and hence less impedance. Boards like the 8KHA+ that have the ATX connector right next to the voltage regulator, however, shouldn't have this problem. People whine about draping the ATX bundle above the CPU without realizing that putting the connector on the far right of the board jeapordizes signal quality.


    "Makes me think it would be a good idea to look for a PSU that comes with a 9amp ATX plug instead of the standard 6amp plug."

    I've been looking for that too, even though I think it is only a temporary solution. It would be better in the long run to adopt EPS12V (used for duallies and servers,) which has more power pins, I believe, and thus can handle much more loading on each individual rail...
    Last edited by causticVapor; 05-01-2003 at 06:55 AM.

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