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ATX mainboard question

Discussion in 'Electronic Repair' started by Sam Goldwasser, Aug 17, 2003.

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  1. Would NOT having memory or any peripherals plugged in prevent
    an ATX power supply from turning on? I'm not referring to an
    SMPS loading issue but an actual logic lockout. I can force the
    power supply on by grounding the PWR-ON (green) wire but the
    tower case power button has no effect. It is receiving some
    voltage and does ground the power-on pin on the mainboard (which
    is of course NOT directly connected to PWR-ON of the power
    supply) when depressed but has absolutely no effect.

    It's from a Compaq mini-tower.

    The story I got was that this started when a new video card
    was plugged in, possibly askew. However, that story is
    somewhat jumbled so I don't have a lot of confidence in it.

    Is the computer likely to boot and run properly "hot wired"
    or is there some reset/initialization that really requires
    the proper power on sequence?

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at repairfaq.org. Thanks.
     
  2. Dave D

    Dave D Guest

    Try clearing the CMOS Sam, I've lost count of the number of times I've
    encountered apparently 'dead' boards after installing or removing PCI/AGP
    peripherals. I've also encountered mobos which won't power up with dead CMOS
    batteries. Does the mobo actually work when you force the power on?

    Dave
     
  3. BOB URZ

    BOB URZ Guest

    I had a compac the other day i was working on that was dead. Swapped the
    PS, no change. thought for sure it was the MB. Got a OEM MB off of ebay
    (SD-11 or such original spare). put it in and it was still dead. WTF?
    Turned out the video card (AGP) and modem card were shorted or such
    and causing the board NOT to start up. I swapped in different cards, and all
    was well. I then tested the old MB, and it started up now and ran.
    The memory was OK.

    BOB

    So the moral of the story, bad or shorted plug in cards can cause a no
    start situation.

    BOB
     
  4. Jason D.

    Jason D. Guest

    This is usually made by Mitac. Junkie.
    Even with CMOS battery in peecees, usually not a big problem for the
    power control. The power management is with multi i/o stuff,
    keyboard/mouse PS/2 ports controller intergrated into one 100 pin IC.
    IC is powered by 5Vsb from the ATX PSU. Fixed a dead motherboard (Asus
    P2B) this way by swapping that IC from another board. Check the IC
    markings for compatiable swap, last few numbers is version numbers.

    USB and cmos battery is routed to the southbridge.

    Oh, you can do a power on test without cpu, memory with that power
    button attached. Then CPU and listen for beeps, almost always does
    this bec of no ram and no video. Push power button and hold 4 sec to
    turn off.

    That IC also allows option (set in bios settings) to use keyboard to
    turn on computer.

    Cheers,

    Wizard
     
  5. That's what I need to check next but will have to wait until I can
    snag a memory card to put in it.

    Thanks.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at repairfaq.org. Thanks.
     
  6. The PC is a Compaq Presario, proabably one of the 7400 series though I
    can't find a model number anywhere. The mainboard configuration and
    jumper options seem to match.

    So, I cleared the CMOS and installed a 256 MB DIMM.

    Now it powers up and down fine. When powred on, or RESET, it goes through
    the memory test. At 120 MB, the screen gets totally hosed and it hangs there.
    The only key on the KB that has any effect is F9 which causes it to
    terminate the memory test with "248 MB OK" (before it gest to 120 MB,
    after it's ignored), move the FDD heads once or twice, then hang. No
    amount of random key hitting has any effect (other than that F9).

    According to

    http://h18000.www1.hp.com/support/FAQs/desktops.html
    (and the 7400 maintenance and troubleshooting guide),
    F10 should start SETUP but F10 has absolutely no effect
    at any time.

    As far as I can tell, the jumpers for CPU clock multiplier, bus speed,
    and core power are set correctly based on the label on the CPU chip.

    What am I overlooking? Or is the BIOS corrupted or something more serious?

    Thanks to all.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at repairfaq.org. Thanks.
     
  7. Dave D

    Dave D Guest

    A long shot- is the memory fast enough for the CPU bus speed? installing a
    PC100 Dimm where a PC133 is required, or a PC66 where PC100 is required can
    cause these symptoms. Some systems don't even like it when *faster* memory
    is used, though usually that is laptops.

    Failing that, it could be bad memory or, quite simply, a buggered
    motherboard. You could try altering the memory settings in the CMOS (the CL
    rating) if it provides that facility, (not bloody likely with Compaq!) but
    it is a long shot.

    Dave
     
  8. Dave D

    Dave D Guest

    It just occured to me, the motherboard might not support this configuration.
    It might work with only single sided 256MB, only double sided 256MB etc. The
    reason I mention this is that it counts almost half the Dimm then fails.
    It's only a hunch but it's worth checking out.

    Dave
     
  9. Both your suggestions may have validity. The memory is a PC133 and the
    bus is I guess 97 MHz.

    I'll see what other memory I can find as well as checking the specs
    of the mainboard.

    Thanks.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at repairfaq.org. Thanks.
     
  10. none

    none Guest

    Correct. The Intel BX does not support single sided 256MB DIMMS. There are
    probably other chipsets that won't work as well.
     
  11. The PC is a Compaq Presario, proabably one of the 7400 series though I
    Compaq. That one word makes me reluctant to continue.
    Look up the cost of a new ATX motherboard suitable for whatever CPU
    you have. When you've finished being surprised how cheap it is, buy
    one and set up again free of Compaq's non-standard annoyances.
     
  12. Dave D

    Dave D Guest

    I do stuff like that. I can't explain why I do it, it's just addictive I
    suppose :)

    Dave
     
  13. Well, Win98 is running fine on it now. The only remaining issue is to
    find the proper driver for the on-board video. It looks like I can download
    it from the Compaq Web site.

    Sorry, I agree with you about Compaq. But I'm not doing this because I
    need another PC. Just can't stand to see it go to waste. :) And, so
    far, I really haven't seen that much to complain about.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at repairfaq.org. Thanks.
     
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