diagnose cpu or mobo ?

Discussion in 'A+ Certification' started by Frank_G, Mar 6, 2004.

  1. Frank_G

    Frank_G Guest

    I have been presented with a dead computer.

    No boot, no beeps, no post - just a little 'sound' action at the very
    beginning and then nothing.

    The fan's running & the led lights are on & I've used the 'back probe'
    technique to check the voltage from the power supply and it seems fine at 5V

    All connector's appear to be seated in their sockets.

    I tried replacing with a known-good stick of ram.

    I tried replacing the video card. There are no other pci cards.

    Without a post card, or a spare known-good cpu, is there any way to tell if
    it's the cpu or mobo ?

    Any other ideas - perhaps I've overlooked the obvious ?

    --
    xx
    Frank_G, Mar 6, 2004
    #1
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  2. Frank_G

    Frank_G Guest


    > I have been presented with a dead computer.
    >
    > No boot, no beeps, no post - just a little 'sound' action at the very
    > beginning and then nothing.
    >
    > The fan's running & the led lights are on & I've used the 'back probe'
    > technique to check the voltage from the power supply and it seems fine at

    5V
    >
    > All connector's appear to be seated in their sockets.
    >
    > I tried replacing with a known-good stick of ram.
    >
    > I tried replacing the video card. There are no other pci cards.
    >
    > Without a post card, or a spare known-good cpu, is there any way to tell

    if
    > it's the cpu or mobo ?
    >
    > Any other ideas - perhaps I've overlooked the obvious ?
    >

    ============================================
    just after I posted, I spoke to someone who said that 5v is way to low to
    give enough power to boot - my digital multimeter is set at DC volts and
    it's auto ranging - my friend said it should read about 32 mV - it's an
    older supply about 150W
    Frank_G, Mar 6, 2004
    #2
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  3. Frank_G

    jim6538 Guest

    I had one on the bench the other day. No post no beeps no nothing. It
    didn't even spin any fans. Push the power button and nothing. Power
    supply gave 5v and 12v solid. It turned out to be a short on the logic
    board of the hard drive. It was the first resistor in from the 5v
    connection. I scavenged a logic board and replaced it to retrieve the
    data.(user had no backup). New HD got it out the door.


    On Sat, 6 Mar 2004 11:15:51 -0500, "Frank_G" <>
    wrote:

    >I have been presented with a dead computer.
    >
    >No boot, no beeps, no post - just a little 'sound' action at the very
    >beginning and then nothing.
    >
    >The fan's running & the led lights are on & I've used the 'back probe'
    >technique to check the voltage from the power supply and it seems fine at 5V
    >
    >All connector's appear to be seated in their sockets.
    >
    >I tried replacing with a known-good stick of ram.
    >
    >I tried replacing the video card. There are no other pci cards.
    >
    >Without a post card, or a spare known-good cpu, is there any way to tell if
    >it's the cpu or mobo ?
    >
    >Any other ideas - perhaps I've overlooked the obvious ?
    jim6538, Mar 7, 2004
    #3
  4. Frank_G

    Frank_G Guest

    Thanks to all replies. I figure it's the mobo - here's the story:

    Fortunately, I had the identical unit available tonight on loan, in good
    working
    order, to swap parts.
    I used 1 x stick of known good ram.
    I replaced the psu with the known good one.
    I replaced the cpu (difficult darned clips to manage - the old zif lever was
    so much easier - but I digress:) with a known good one.
    Still no action - no beeps, no post, nothing. Just a bit of sound of some
    action at the very beginning.
    I didn't worry much about the video card, or the ribbon cable to the hard
    drive as I figured if they were the cause, I'd at least get some beeps -
    correct? Or .......mmmmm......if there's a problem with the HD (e.g. a
    short) could this have created the symptom as jim6538 has just suggested? I
    wouldn't have been so eager to get the borrowed machine back together again
    and returned to it's owner, If I'd read jim's post first.

    By deduction, would you agree that it's the mobo ?
    If so, I guess the machine is toast, maybe salvage a few parts for the
    future.

    And Doug you're right about the voltage (Vm being a fraction of V)
    I inserted the red probe into pin 8/ the gray colour wire only - and with
    the psu on - I
    read each of the 2 machines the same way. The mystery is that the "bad"
    machine had the "good" reading of DC 5V and the "good" machine had the "bad"
    reading of a fractional 32 mili-volts (Vm) - go figure.

    ===============================================
    > I have been presented with a dead computer.
    >
    > No boot, no beeps, no post - just a little 'sound' action at the very
    > beginning and then nothing.
    >
    > The fan's running & the led lights are on & I've used the 'back probe'
    > technique to check the voltage from the power supply and it seems fine at

    5V
    >
    > All connector's appear to be seated in their sockets.
    >
    > I tried replacing with a known-good stick of ram.
    >
    > I tried replacing the video card. There are no other pci cards.
    >
    > Without a post card, or a spare known-good cpu, is there any way to tell

    if
    > it's the cpu or mobo ?
    >
    > Any other ideas - perhaps I've overlooked the obvious ?
    >
    > --
    > xx
    >
    >
    Frank_G, Mar 7, 2004
    #4
  5. Frank_G

    Frank_G Guest

    no, it's not the HD - just tested it



    > Thanks to all replies. I figure it's the mobo - here's the story:
    >
    > Fortunately, I had the identical unit available tonight on loan, in good
    > working
    > order, to swap parts.
    > I used 1 x stick of known good ram.
    > I replaced the psu with the known good one.
    > I replaced the cpu (difficult darned clips to manage - the old zif lever

    was
    > so much easier - but I digress:) with a known good one.
    > Still no action - no beeps, no post, nothing. Just a bit of sound of some
    > action at the very beginning.
    > I didn't worry much about the video card, or the ribbon cable to the hard
    > drive as I figured if they were the cause, I'd at least get some beeps -
    > correct? Or .......mmmmm......if there's a problem with the HD (e.g. a
    > short) could this have created the symptom as jim6538 has just suggested?

    I
    > wouldn't have been so eager to get the borrowed machine back together

    again
    > and returned to it's owner, If I'd read jim's post first.
    >
    > By deduction, would you agree that it's the mobo ?
    > If so, I guess the machine is toast, maybe salvage a few parts for the
    > future.
    >
    > And Doug you're right about the voltage (Vm being a fraction of V)
    > I inserted the red probe into pin 8/ the gray colour wire only - and with
    > the psu on - I
    > read each of the 2 machines the same way. The mystery is that the "bad"
    > machine had the "good" reading of DC 5V and the "good" machine had the

    "bad"
    > reading of a fractional 32 mili-volts (Vm) - go figure.
    >
    > ===============================================
    > > I have been presented with a dead computer.
    > >
    > > No boot, no beeps, no post - just a little 'sound' action at the very
    > > beginning and then nothing.
    > >
    > > The fan's running & the led lights are on & I've used the 'back probe'
    > > technique to check the voltage from the power supply and it seems fine

    at
    > 5V
    > >
    > > All connector's appear to be seated in their sockets.
    > >
    > > I tried replacing with a known-good stick of ram.
    > >
    > > I tried replacing the video card. There are no other pci cards.
    > >
    > > Without a post card, or a spare known-good cpu, is there any way to tell

    > if
    > > it's the cpu or mobo ?
    > >
    > > Any other ideas - perhaps I've overlooked the obvious ?
    > >
    > > --
    > > xx
    > >
    > >

    >
    >
    Frank_G, Mar 7, 2004
    #5
  6. Frank_G

    Frank_G Guest

    I just swopped parts from the 'bad' machine to the 'good' machine - the hard
    drive, video card, cpu and each in turn worked ok.
    So the chances are it is the mb.
    Not to discount what you say about mountings et al.
    I cant check the mobo - I dont think I'm willing to remove it from the bad
    machine and install it in the good machine :)

    > Although it probably IS the motherboard, your logic in excluding the
    > vidoe card and hard drive is faulty. In fact, almost ANYTHING can cause
    > this symptom, including hardware (literally -- screws & motherboard
    > mounting hardware) and configuration errors. If the system WAS working
    > and quit, it's easier to troubleshoot.
    >
    >
    > Frank_G wrote:
    > > Thanks to all replies. I figure it's the mobo - here's the story:
    > >
    > > Fortunately, I had the identical unit available tonight on loan, in good
    > > working
    > > order, to swap parts.
    > > I used 1 x stick of known good ram.
    > > I replaced the psu with the known good one.
    > > I replaced the cpu (difficult darned clips to manage - the old zif lever

    was
    > > so much easier - but I digress:) with a known good one.
    > > Still no action - no beeps, no post, nothing. Just a bit of sound of

    some
    > > action at the very beginning.
    > > I didn't worry much about the video card, or the ribbon cable to the

    hard
    > > drive as I figured if they were the cause, I'd at least get some beeps -
    > > correct? Or .......mmmmm......if there's a problem with the HD (e.g. a
    > > short) could this have created the symptom as jim6538 has just

    suggested? I
    > > wouldn't have been so eager to get the borrowed machine back together

    again
    > > and returned to it's owner, If I'd read jim's post first.
    > >
    > > By deduction, would you agree that it's the mobo ?
    > > If so, I guess the machine is toast, maybe salvage a few parts for the
    > > future.
    > >
    > > And Doug you're right about the voltage (Vm being a fraction of V)
    > > I inserted the red probe into pin 8/ the gray colour wire only - and

    with
    > > the psu on - I
    > > read each of the 2 machines the same way. The mystery is that the "bad"
    > > machine had the "good" reading of DC 5V and the "good" machine had the

    "bad"
    > > reading of a fractional 32 mili-volts (Vm) - go figure.
    > >
    > > ===============================================
    > >
    > >>I have been presented with a dead computer.
    > >>
    > >>No boot, no beeps, no post - just a little 'sound' action at the very
    > >>beginning and then nothing.
    > >>
    > >>The fan's running & the led lights are on & I've used the 'back probe'
    > >>technique to check the voltage from the power supply and it seems fine

    at
    > >
    > > 5V
    > >
    > >>All connector's appear to be seated in their sockets.
    > >>
    > >>I tried replacing with a known-good stick of ram.
    > >>
    > >>I tried replacing the video card. There are no other pci cards.
    > >>
    > >>Without a post card, or a spare known-good cpu, is there any way to tell

    > >
    > > if
    > >
    > >>it's the cpu or mobo ?
    > >>
    > >>Any other ideas - perhaps I've overlooked the obvious ?
    > >>
    > >>--
    > >>xx
    > >>
    > >>

    > >
    > >
    > >

    >
    Frank_G, Mar 7, 2004
    #6
  7. Frank_G

    Frank_G Guest


    >
    > Power supplies are buggers to diagnose - if you don't have a sufficient

    load
    > on them they'll shut down and give you a (near) zero output. And (assuming
    > it's an ATX PSU) I wouldn't use Pin 8 because it's just a monitor level.
    >
    > It's not a Dell, is it? They've got different pinouts:
    > http://165.193.123.52/articles/upgrade3_01_01.asp


    no, it's an older IMB PC300GL.

    I used the #8 pin (gray colour) as per 'upgrading & repairing pc's' as per
    page 1171 & 1141 - also known as the 'power good' pin
    Frank_G, Mar 7, 2004
    #7
  8. Frank_G

    Frank_G Guest

    just tried that - connected the HD, video card, cpu, 1 stick ram, psu - but
    no luck


    > Try removing it and seeing if it will run sitting on a non-conductive
    > work surface, not installed into a case at all.
    >
    >
    > Frank_G wrote:
    > > I just swopped parts from the 'bad' machine to the 'good' machine - the

    hard
    > > drive, video card, cpu and each in turn worked ok.
    > > So the chances are it is the mb.
    > > Not to discount what you say about mountings et al.
    > > I cant check the mobo - I dont think I'm willing to remove it from the

    bad
    > > machine and install it in the good machine :)
    > >
    > >
    > >>Although it probably IS the motherboard, your logic in excluding the
    > >>vidoe card and hard drive is faulty. In fact, almost ANYTHING can cause
    > >>this symptom, including hardware (literally -- screws & motherboard
    > >>mounting hardware) and configuration errors. If the system WAS working
    > >>and quit, it's easier to troubleshoot.
    > >>
    > >>
    > >>Frank_G wrote:
    > >>
    > >>>Thanks to all replies. I figure it's the mobo - here's the story:
    > >>>
    > >>>Fortunately, I had the identical unit available tonight on loan, in

    good
    > >>>working
    > >>>order, to swap parts.
    > >>>I used 1 x stick of known good ram.
    > >>>I replaced the psu with the known good one.
    > >>>I replaced the cpu (difficult darned clips to manage - the old zif

    lever
    > >
    > > was
    > >
    > >>>so much easier - but I digress:) with a known good one.
    > >>>Still no action - no beeps, no post, nothing. Just a bit of sound of

    > >
    > > some
    > >
    > >>>action at the very beginning.
    > >>>I didn't worry much about the video card, or the ribbon cable to the

    > >
    > > hard
    > >
    > >>>drive as I figured if they were the cause, I'd at least get some

    beeps -
    > >>>correct? Or .......mmmmm......if there's a problem with the HD (e.g. a
    > >>>short) could this have created the symptom as jim6538 has just

    > >
    > > suggested? I
    > >
    > >>>wouldn't have been so eager to get the borrowed machine back together

    > >
    > > again
    > >
    > >>>and returned to it's owner, If I'd read jim's post first.
    > >>>
    > >>>By deduction, would you agree that it's the mobo ?
    > >>>If so, I guess the machine is toast, maybe salvage a few parts for the
    > >>>future.
    > >>>
    > >>>And Doug you're right about the voltage (Vm being a fraction of V)
    > >>>I inserted the red probe into pin 8/ the gray colour wire only - and

    > >
    > > with
    > >
    > >>>the psu on - I
    > >>>read each of the 2 machines the same way. The mystery is that the "bad"
    > >>>machine had the "good" reading of DC 5V and the "good" machine had the

    > >
    > > "bad"
    > >
    > >>>reading of a fractional 32 mili-volts (Vm) - go figure.
    > >>>
    > >>>===============================================
    > >>>
    > >>>
    > >>>>I have been presented with a dead computer.
    > >>>>
    > >>>>No boot, no beeps, no post - just a little 'sound' action at the very
    > >>>>beginning and then nothing.
    > >>>>
    > >>>>The fan's running & the led lights are on & I've used the 'back probe'
    > >>>>technique to check the voltage from the power supply and it seems fine

    > >
    > > at
    > >
    > >>>5V
    > >>>
    > >>>
    > >>>>All connector's appear to be seated in their sockets.
    > >>>>
    > >>>>I tried replacing with a known-good stick of ram.
    > >>>>
    > >>>>I tried replacing the video card. There are no other pci cards.
    > >>>>
    > >>>>Without a post card, or a spare known-good cpu, is there any way to

    tell
    > >>>
    > >>>if
    > >>>
    > >>>
    > >>>>it's the cpu or mobo ?
    > >>>>
    > >>>>Any other ideas - perhaps I've overlooked the obvious ?
    > >>>>
    > >>>>--
    > >>>>xx
    > >>>>
    > >>>>
    > >>>
    > >>>
    > >>>

    > >
    > >

    >
    Frank_G, Mar 7, 2004
    #8
  9. Frank_G

    Tom Guest

    In article <fgH2c.14$>,
    says...
    >
    > >
    > > Power supplies are buggers to diagnose - if you don't have a sufficient

    > load
    > > on them they'll shut down and give you a (near) zero output. And (assuming
    > > it's an ATX PSU) I wouldn't use Pin 8 because it's just a monitor level.
    > >
    > > It's not a Dell, is it? They've got different pinouts:
    > > http://165.193.123.52/articles/upgrade3_01_01.asp

    >
    > no, it's an older IMB PC300GL.
    >
    > I used the #8 pin (gray colour) as per 'upgrading & repairing pc's' as per
    > page 1171 & 1141 - also known as the 'power good' pin
    >
    >
    >

    I have serviced alot of these over the past year or so. Most of the
    ones I have worked on (circa 1997\98 models) had dead or dying CMOS
    batteries that had to be replaced.
    Tom, Mar 7, 2004
    #9
  10. Frank_G

    Frank_G Guest


    > > > Power supplies are buggers to diagnose - if you don't have a

    sufficient
    > > load
    > > > on them they'll shut down and give you a (near) zero output. And

    (assuming
    > > > it's an ATX PSU) I wouldn't use Pin 8 because it's just a monitor

    level.
    > > >
    > > > It's not a Dell, is it? They've got different pinouts:
    > > > http://165.193.123.52/articles/upgrade3_01_01.asp

    > >
    > > no, it's an older IMB PC300GL.
    > >
    > > I used the #8 pin (gray colour) as per 'upgrading & repairing pc's' as

    per
    > > page 1171 & 1141 - also known as the 'power good' pin
    > >
    > >
    > >

    > I have serviced alot of these over the past year or so. Most of the
    > ones I have worked on (circa 1997\98 models) had dead or dying CMOS
    > batteries that had to be replaced.


    A dead battery would simply not hold the bios settings, surely? Not display
    symptoms as per original post?
    Frank_G, Mar 7, 2004
    #10
  11. 32 millivolts? uhh... if LEDs are lighting up, you have a little bit
    more than 32 millivolts

    perhaps you meant 32 milliamps?

    > just after I posted, I spoke to someone who said that 5v is way to

    low to
    > give enough power to boot - my digital multimeter is set at DC volts

    and
    > it's auto ranging - my friend said it should read about 32 mV - it's

    an
    > older supply about 150W
    Solomon Kozanski, Sep 8, 2004
    #11
  12. On Wed, 8 Sep 2004 09:01:11 -0400, "Solomon Kozanski"
    <> wrote:

    >32 millivolts? uhh... if LEDs are lighting up, you have a little bit
    >more than 32 millivolts


    A conducting LED should have 1.2-1.5 volts across it, if I remember
    correctly.

    Tom

    >
    >perhaps you meant 32 milliamps?
    >
    >> just after I posted, I spoke to someone who said that 5v is way to

    >low to
    >> give enough power to boot - my digital multimeter is set at DC volts

    >and
    >> it's auto ranging - my friend said it should read about 32 mV - it's

    >an
    >> older supply about 150W
    Tom MacIntyre, Sep 8, 2004
    #12
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