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Thread: Need validation of cause of PSU issue at startup

  1. #1
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    Need validation of cause of PSU issue at startup

    I've searched the forum and FAQs and have found a few threads with similar issues, but nothing that can conclusively help me solve my issue. Here's my system spec, problem and things I've tried:

    Problem:
    The PSU LED lights up for 1 second when connected to my AC/DC power brick, which I am using for bench operation. I power it with a brick that use a "plug n" barrel, that is mated to the PSU's power plug. The brick I am using is pretty hefty in spec, 120W/10A/12v, and is the one recommended in numerous threads and sites for this kind of operation:



    CarPC spec:
    Zotac GF9300-I-E Mobo
    INTEL PENTIUM D CPU 2.8GHz/2M/800/05A SL88T Socket 775 Proc
    Samsung 2x1GB 800Mhz DDR2 RAM
    iMation 64GB SSD
    120W Pico PSU
    PCIe slot is empty

    This problem only happens when I connect the 4 prong CPU power plug to the MoBo. When not connected, the PSU stays on, the LED stays lit and the fan stays on. But of course, no proc power, no post.

    The proc rates out like this, in terms of power consumption, which appears to be my problem:
    Pentium-D 820 - (dual 2.8GHz - 2x 1MB) 1.4V
    (1.2V~1.4V) 1.55V 100A 95W W 63 C

    Things I have tried:
    I used a standard desktop PSU rated at 240W and the machine posts fine. I installed Windows 7 using the desktop PSU.

    Preliminary conclusions:
    Everything above seems to suggest I am not getting enough power through the 12v rail and thus to the CPU at startup. This causes a protect circuit in the on board PSU to shut things down.

    Questions:
    Does this sound right to you?
    Does the CPU draw max power at startup? If so, the above makes sense. If not, there should be more than enough idle power to at least get the PC to post and boot.
    I am not concerned about the brick's ability to provide adequare power to the CarPC, given the 12v/10A/120W rating. Should I be concerned?

    Thanks in advance for your thoughts.

    Pics:





  2. #2
    Constant Bitrate meryan00's Avatar
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    I'm no expert, but it sounds right on. Looking at your PicoPSU it has a peak on the 12V rail of only 10A with max continuous at 7A and total max output of 140W( if fan-cooled). With your fans, HD and MB in addition to your Desktop CPU I'd guess it is to much. The Pico PSU even suggests mobile or low power processors and 95W is not exactly low copmared to what is available now.

    Honestly I would suggest looking into the M2-ATX since your case is already made to hold it. That should give you enough overhead to get things going for the lowest cost.

    Short of that check other CPus that will fit your Mobo for example the Celeron E3400 is close but only 65W it might do the job http://www.newegg.com/Product/Produc...82E16819116348

  3. #3
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    Thanks!

    I have seen a few threads where guys bought the M2 and had the same problem, which ended up being the result of a non-PSU issue. I wanted to make sure I wasn't missing something before buying another PSU.

  4. #4
    MySQL Error soundman98's Avatar
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    DON'T USE THE PICO PSU IN-CAR!!!!!

    it doesn't provide regulated power on the 12v line(car power varies from 5v to 15v, and this psu will pass this on to the motherboard), and has the potential to fry all of the carpc components..

    i use a dsatx with the same board and a pentium dual core-- though, that will not fit in that case..

  5. #5
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    Quote Originally Posted by soundman98 View Post
    DON'T USE THE PICO PSU IN-CAR!!!!!

    it doesn't provide regulated power on the 12v line(car power varies from 5v to 15v, and this psu will pass this on to the motherboard), and has the potential to fry all of the carpc components..

    i use a dsatx with the same board and a pentium dual core-- though, that will not fit in that case..
    Done deal...consider it gone. I have to say that I didn't consider the proc power needs well enough. The Pent D is THIRSTY and even the M2 seems a bit light on juice and the bigger PSUs don't seem to fit my case by default. I'll figure out my options and post shortly.

  6. #6
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    The DSATX is the only PSU that will safely provide the Pent D with the power needed, plus lots of buffer, to run it at peak operating voltage and draw from the 12v rail. But, DAMN is it expensive!

    The M4-ATX is a reasonable alternative, with a decent buffer, although its peak wattage on the 12V rail is less than the DSATX.

    The M2ATX 160W is right on the razor's edge, able to provide 96W on the 12v rails without bleeding into peak voltage, which is 1W more than the Thermal Design Power limit of my chip. The TDP isn't the max possible draw for the chip, though, just the design limit, so theoretically, one could overdraw the PSU. That said, this CarPC will just be playing MP3s and Lossless audio, so is there really that much possibility of this miniscule risk biting me?

    I am leaning toward the M2, since it fits my case.

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