OT?: Major PC hardware failure

Discussion in 'Asus' started by Puddin' Man, Apr 6, 2011.

  1. Puddin' Man

    Puddin' Man Guest

    I built a pc around Pentium cpu, Intel D865GVHZ board, Antec case/PS back in '06.
    Have been running it about 16 hours/day ever since.

    Whilst running a backup Sunday, I heard a constant little tic-tic, tic-tic,
    tic-tic sound, looked down to find Speedfan registered about 74 C. then watched
    the W2k system crash.

    I immediately suspected a cpu fan failure, but all fans were running when I checked.
    I replaced the cpu fan anyway. This morn it wouldn't even POST, showed only an
    "Intel board" screen. A bit later it wouldn't power at all (no fans. lights,

    The Power Supply is Antec Smart-Power 350w. It could have gone bad and overjuiced
    the cpu causing the 74 C. temp? After which the Intel overheated-cpu
    function started shutting everything down?

    I've not had a system fail in this manner. Hope someone has some idea
    what happened.


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 6, 2011
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  2. Puddin' Man

    Paul Guest

    Have a look at your Southbridge. You just had a latchup failure
    on your ICH5 :)

    Because the motherboard won't start, that means you had a major failure.
    Your ICH5 or ICH5R should look like this. (Back in that era, the
    Southbridge didn't have a heatsink on it. The Northbridge, usually does.
    The Southbridge is the chip you can visually inspect, without taking
    anything apart.)


    It would be fun to ask the warranty people at Intel, how many of
    those blew. Musta been a few. It's a semiconductor problem,
    not publicly acknowledged by Intel. Gigabyte is the only company
    to post a warning about the problem.

    Replace the motherboard, and your other components should be
    OK. I haven't heard of collateral damage from that. It's just
    the Southbridge which is "toast".

    The burn mark in the picture, is over top of the contacts underneath,
    which power USB I/O. A possible explanation, is static electricity
    enters via a USB port, and causes the USB I/O pad to go into latchup.
    That causes a conducting path to form between VCC and GND. If the bond
    wires burn out, it's called a "minor failure" and you lose all your USB
    interfaces. There would be no burn mark in that case, because the
    bond wires let go, before anything gets fried. Device Manager
    still shows USB entries (because the logic blocks are intact), but
    no plugged in devices are detected. Since the bond wire is burned out,
    the D+ and D- signals can no longer receive info from USB peripherals.

    If the bond wires remain intact during the event, the chip heats up until
    a hole is burned in the lid. The silicon is ruined, and the board will no longer

    While Gigabyte claimed, in their warning, that ICH4 and ICH5 were affected,
    the vast majority of reported failures in newsgroups are ICH5. I think
    I've only read one report of an ICH4 blowing.

    Paul, Apr 6, 2011
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  3. Puddin' Man

    Puddin' Man Guest

    Hi Paul,

    I saved your notes re ICH5 problems some time ago.

    My Southbridge has markings:
    I N T E L
    [email protected]@'02

    and it's square, unlike on your link below.

    And there's NO evidence of burnout. The chip and it's
    peripheral connections look OK.

    At the time of failure, I got RUNDLL Message Popup. Since then I get:

    "The CPU was previously shutdown due to a thermal event(overheating)
    Service the unit right away to resolve this"

    Any/all advice on getting the unit "serviced" much appreciated.

    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 7, 2011
  4. Puddin' Man

    Paul Guest

    OK, have you pulled the CPU heatsink/fan and checked for damage ?
    Do you still have thermal paste between the CPU and heatsink ?

    Maybe the Vcore circuit overvolted and ran the CPU at higher than
    normal voltage ? The last datasheet I looked at, Vcore is supposed
    to have a check for overvoltage - the regulator will shut down,
    if the output is off by a certain percentage or more. So normally
    you're protected from that.

    The Vcore circuit doesn't have "total control", and I suppose it
    would be possible for a fault to occur, that the regulator chip
    cannot stop. Only a certain class of faults can be detected
    by the regulator chip, and stopped relatively quickly.


    The processor has two levels of thermal protection. It uses throttling
    first, to try to stop the overheat. If it gets too hot, it uses
    THERMTRIP, which should cause the power supply to shut off.

    THERMTRIP or a Vcore failure, might be latching faults. That means,
    to clear then, all power must be removed by the computer. The easiest
    way to do that, is to flip the rear switch to OFF for 60 seconds, then
    flip it back on again.


    Relative to other components in the computer, processors are
    extremely reliable. It is possible for a silicon die to crack,
    if it's under enough mechanical stress. And perhaps a resulting
    short circuit on the die, can result in overheating.

    The only reason I'm not blaming your power supply at all, is
    your observation of the ongoing overtemperature indication,
    which would be coming from the processor. Vcore can handle excursions
    on +12V, without transferring that through to the processor. So if
    the 12V shot up to 16V for example, it might fry all the hard
    drives, but it wouldn't bother Vcore at all. Onboard regulators
    help to "insulate" motherboard components, from power supply
    problems. Components directly connected to the supply (PCI cards,
    hard drives) are more at risk.

    So right now, all I can suggest, is check to see whether the
    heatsink is firmly attached to the motherboard. Sometimes, a plastic
    latch snaps or the like. Also, visually inspect the capacitors
    around the motherboard socket, for bulging or leakage.



    On some motherboards, the Northbridge heatsink falls off, when the
    solder joint fails on the steel wire holding the heatsink to the
    motherboard. Your symptoms don't seem to be consistent with that,
    but you can check the Northbridge heatsink for being securely in
    place, while you're doing your other inspections. At least one
    Dell computer, electrically checks that the heatsink is secure, and
    the computer won't boot unless the mechanical wire is soldered
    back into place.

    Paul, Apr 7, 2011
  5. Puddin' Man

    Eric Parker Guest

    I'd test the PSU.
    Disconnect all leads from the M/B, drives etc.
    Short the green (PS_ON#) to black (Com) and check the voltages.
    See http://www.smpspowersupply.com/connectors-pinouts.html

    Around 06 I built 4 systems based on Antec cases with PSUs.
    3 out the four PSUs malfunctioned and destroyed M/Bs and drives within about
    a month of each other.
    I changed the PSU in the fourth and the system is still running.

    Eric Parker, Apr 7, 2011
  6. Puddin' Man

    Puddin' Man Guest

    I installed new HS/fan with paste the night it crashed.
    Sounds likely.
    I've done that numerous times. No help.
    Check. I've installed a new PS and it's made no difference
    in system behavior. Problem persists.
    The primary HD didn't fry: looked OK on the other pc. There
    were no PCI cards.
    All that has been done. No evident problem.
    The Northbridge heatsink is fine. Everything on the board looks OK.

    I power it up for about 20 secs, then it shuts all power down.
    Should there be some sort of Vcore reset in bios? Any other way
    to effect a reset?


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 7, 2011
  7. Puddin' Man

    Puddin' Man Guest

    I'll assume the Antecd PS caused the problem 'till I have evidence
    to the contrary.

    I have new Extreme 460w PS installed: problem persists.

    Never again Antec PS for me.


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 7, 2011
  8. Puddin' Man

    Paul Guest

    Your D865GVHZ should have THERMTRIP, and shutting off after 20 seconds
    could be due to that. The BIOS obviously has the skill set to shut
    off the computer too, but then the question would be, why. Some
    BIOS will check for a minimum fan rotation speed on the CPU fan,
    and shut off the computer if they don't detect it. That would be for
    the CPU fan, while other fans are allowed to die if they want. Usually,
    on the CPU fan would be considered as a reason to shut off the

    Vcore is programmable a couple ways.

    On a non-enthusiast motherboard, they would use the facilities provided
    by default. The processor has VID signals on the bottom of it. The bit
    pattern specifies a voltage. Those can be connected directly to a
    similar interface on the Vcore regulator chip. Modern processors even
    adjust that voltage dynamically, as a function of computing load
    (a feature of Intel SpeedStep, otherwise known as EIST).

    On an enthusiast motherboard, the Vcore may have an additional input feature,
    that allows adding an offset to the "regular" voltage value. That is used
    when overclocking. On my last motherboard, I found a pin on the
    Vcore regulator, by which I could offset the voltage by 0.1 volts, so I could
    try overclocking (even though the motherboard didn't support it). When a
    BIOS supports such a feature, there is an actual Vcore setting in the BIOS
    screen (sometimes it'll be "+0.1" implying a bump of 0.1 volts, rather than
    the BIOS screen giving an absolute voltage as such).

    Your Intel board probably doesn't have that, and just uses the VID code as
    it comes from the processor and goes to Vcore. Since you can't boot the
    system right now, there is no way to get into Windows and use CPUZ, to check
    what CPUZ sees as the current Vcore value. I also checked the user manual
    for the motherboard, and I don't see a hardware monitor page in there. One
    option would have been, to use the 20 seconds to visit the hardware monitor
    page and check a Vcore reading there. (Some SuperI/O chips have eight channels
    of ADC or analog to digital conversion, for making crude 8 bit voltage measurements.
    They use that to measure the three main power supply rails, Vcore, and present
    that in a BIOS hardware monitor page.)

    Without that, you'd have to get out a multimeter, and figure out where to probe,
    if you thought it was actually a Vcore problem.

    Note that, a motherboard can "run" without a processor installed in it. You would
    remove the memory and the processor, and operate with just the bare board.
    Pressing the switch on the front of the computer, with the panel wiring attached,
    should allow the power supply to be turned on and off. In this case, the purpose
    of the test, would be to verify the control circuit is working. If the
    thing still died after 20 seconds, then you'd know it likely wasn't
    the processor. In such a scenario, motherboard running without processor
    installed, the VID signals are "floating", they float to all 1's logic
    value, and VCore gets set to zero volt output when that happens. That
    means effectively, the VCore regulator is not loaded. So the motherboard
    is pretty well neutered. You would expect the power to remain running,
    because many of the "switch-off" mechanisms have been removed.

    I don't particularly see a reason to try a CMOS reset or the like
    in this case. You can try it, but at the very least, remove all
    power from the system before doing it. Intel tends to do things
    differently than other manufacturers, so I don't even know what
    the gotchas are with their procedure. I don't think the BIOS can set
    the voltage to anything dangerous - it doesn't give the impression
    of an enthusiast board when I read the manual. I mean, not finding
    a hardware monitor page, seemed pretty bad. You'd find that feature
    available on a lot of other brands.

    Paul, Apr 7, 2011
  9. Puddin' Man

    Puddin' Man Guest

    Problem persists. Clear CMOS doesn't help.

    I strongly suspect that the "thermal event" kicked THERMTRIP in, and
    that THERMTRIP isn't allowing the default reset that would enable
    resumption of operation (deficiency in THERMTRIP design).

    IIRC, the system has a Winbond chip, and there is a
    temp, etc monitor program (that doesn't function properly).
    Runs under Windoze, of course.

    Thanks for the cpu-less test info: I didn't know about that.

    I have an old Celeron S-478 cpu that I can sub. I guess I'll
    wait until tomorrow, do the cpu-less test, and if it keeps
    "running", install the Celeron, which is not THERMTRIP-ed.

    Many thanks, more info tomorrow.


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 8, 2011
  10. Puddin' Man

    Puddin' Man Guest

    Nothin' works!

    I meant to wait 'till tomorrow, but these thangs bother and bother me,
    and I went ahead and fiddled the damn thang.

    I cleared CMOS again, then pulled cpu and mem. Powered up and ...
    nuthin'!. No fans, no anything.

    Installed old Celeron (which ran in this system years ago), HS/fan
    (w paste), mem. Powered up and ... it spun the fans for a second or
    2, then shut down everything. This is what it has been doing lately:
    a sec or 2 then shut down.

    Beats me. I was hoping at least the board would spin the fans
    w/o cpu, mem.

    Gawd, whotta headache!

    Any ideas? Mobo is now highly suspect??


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 8, 2011
  11. Puddin' Man

    Paul Guest

    OK, remember that, for the empty motherboard to keep the PSU running

    1) Motherboard circuit runs from +5VSB. A fault which overloads +5VSB,
    will cause the power supply to shut off. Asus motherboards have a
    single green LED, connected directly to +5VSB. Such a feature allows
    the user to visually identify +5VSB problems. If the LED winks, instead
    of remaining steady, then you know the problem is related to +5VSB.

    2) An actual overload of the power supply, such as caused by a short
    on the motherboard, will also switch off the power supply. It could be
    something quite innocent, like a pinched speaker wire on the case speaker,
    shorting to ground.

    The bare motherboard test, helps eliminate causes. Since the floating
    VID signals prevent Vcore from running (it's asked to produce a zero
    volt output, effectively disabling it), that means a short circuit
    on Vcore would be unlikely to affect the motherboard PS_ON# signal.

    Your next test, might be to pull the motherboard from the case.
    Connect the two power cables from the PSU. Connect only the front
    panel "Power" button to the header. The purpose of this test case,
    is to eliminate some accidental short when the board is sitting
    inside the computer case.

    If it can't stay running then, it's either motherboard or PSU.
    Trying a second PSU would then point the finger at the motherboard.
    It would be really helpful, to have a way to verify the +5VSB supply
    rail, as it runs the logic that controls PS_ON#. If +5VSB disappears
    for even a fraction of a second, the motherboard can go off until
    you press the power button again. Some users notice their power
    supply is oscillating (+5VSB LED goes on for a second, then goes
    off, repeating forever), which is a sign of an overload or a
    flaky supply. In such a case, I might use my clamp-on DC ammeter,
    clamp it around the +5VSB wire in the main connector harness, and
    see if the current is exceeding the capabilities of the supply.
    A flaky supply, can no longer produce the rated current on +5VSB,
    and if that were the case, it would be the fault of the power supply.
    A typical motherboard might draw around 1 amp from +5VSB, under
    normal conditions (partially depends on whether the NIC is running
    and ready to detect Wake On LAN).

    Sometimes, the problem is an inability of the motherboard, to make
    a good solid logic 0 on the PS_ON# signal. The interface uses open
    collector logic. The motherboard "pulls down" the signal to ground,
    to turn the supply on. (We use the "paper clip test" on a standalone
    supply, to duplicate this "pulling down" thing.) In some cases,
    whatever chip drives PS_ON# on the motherboard, can't make as low
    a signal as is required. If it needs to make a 0.8V or lower level,
    some motherboards leave the signal running at 1.3V to 2.0V. This
    causes the power supply to be "half-on", meaning the power supply
    behaves like it is sick. It's hard to say who is at fault here.
    Either the motherboard driver is too weak, or a fault on the
    power supply is causing its pullup to pull too strongly towards
    the +5VSB rail. Since most users are unequipped to debug or
    document the root cause, there are no records pointing at one
    or the other condition, as being why it happens.

    At one time, motherboards had muscular PS_ON# drive. If the driver chip
    got involved in a fight, smoke should come out :) The driver might
    be a FAST logic open collector 64ma driver, when a lot lower level
    is all that is needed. Today's semiconductor solutions, don't have the
    same "bare knuckles" kinda drive that the older motherboards used.
    Again, without root cause analysis to establish which end is at fault,
    it's hard to say whether the motherboard or PSU design is to blame.
    The PSU end doesn't always use a logic chip, to look at that signal level,
    and in some cases, there might be a transistor used to check the input
    instead. And the characteristics of that, might be unlike a regular
    logic gate input.

    Paul, Apr 8, 2011
  12. Puddin' Man

    Puddin' Man Guest

    The PS is CoolerMaster Extreme+ 460w and was purchased yesterday.

    So, it could be either of:

    1.) Infant mortality of the PS.
    2.) Fried mobo.

    And, all totaled, 2.) is much more likely than 1.).


    For future reference, what is the SB in +5VSB?


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 8, 2011
  13. Puddin' Man

    Paul Guest

    Do you have a working system, in which you could install the
    CoolerMaster, and see if it works ?

    There is a danger, with any "swapping" type testing. We've
    had people in the newsgroups, who have damaged two newly purchased
    items, while searching for a fault. So it's easy to damage a pile of
    stuff, while testing. In retrospect, a trip to a shop might
    be another option. It all depends on whether you feel you want
    to be prepared to do this kind of testing in the future or not
    (i.e. whether a "junk closet" will get used in the future). It's
    really a form of "gambling addition", and in some of the worst
    cases, people end up buying duplicates of most of the hardware
    inside the computer. Sometimes you get lucky, and sometimes you don't.

    Another bad situation, is borrowing a friend's hardware for testing.
    Occasionally, someone will tell a story about sticking his dead
    processor in someone else's computer, and now that computer is dead.
    If you're going to play the "swapping game", it's best to keep it
    in your own house. If you use a shop for testing, they know the
    risks, and part of their fee helps cover the pile of dead stuff.

    I would never consider using a shop, but that's just the way I am.
    And I have had to buy more than one item, to figure it out :)
    So I'm not always lucky, that's for sure.

    I don't really think there is anything wrong with your Coolermaster,
    but testing it in another machine will tell you for sure. It doesn't
    take long to swap out a supply, after you've done it a few times.
    It's just annoying.

    Paul, Apr 8, 2011
  14. Puddin' Man

    Puddin' Man Guest

    The Nahelem-Asus rig, I suppose.
    Thanks for the warning. I wunta done it anyway. :)
    But you figger things out.
    I don't think there is anything wrong with my Coolermaster,
    either, and think that I've id'd the problem to a
    reasonable certainty.

    Please: For future reference, what is the SB in +5VSB?


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 8, 2011
  15. Puddin' Man

    mikea Guest

    "Stand-By": present when the system has been put in "suspend" mode; used
    to power the "wake on <foo>" devices (NIC: wake on LAN; modem: wake on
    dial-in; keyboard: wake on keystroke).

    mikea, Apr 8, 2011
  16. Puddin' Man

    Paul Guest

    It stands for "+5 volts stand by".

    When the computer sleeps, +5VSB continues to run. It may be
    implemented, as two separate power supplies, within the power supply
    box. The +5V standby circuit, isn't particularly efficient.

    You can see why that is, in this diagram. The lower left corner
    shows "second supply" and a 78L05 based linear regulator. A linear
    regulator isn't nearly as efficient as a switching regulator circuit.
    On some power supplies, while the computer sleeps, you may even feel
    a tiny cloud of warm air, near the power supply. (Or perhaps, just
    as the fan starts to spin, when you press the button on the front.)


    The primary side of the supply, charges up the main capacitors
    to a high voltage (like 300 volts DC, or 115 * 1.414 * 2 for voltage
    doubler). Switching circuits, are used to make an A.C. signal from
    that voltage, through the primary side of the various transformers.
    The "second supply", has a switching circuit on its primary side.
    Transformers only pass AC, and that's why it has to be converted
    to AC. A high frequency is used, and the transformers needed are
    relatively small physically. That's how they manage to all fit
    in the box (use of frequencies much higher than 60Hz line frequency).

    But when the voltage comes out the other side, the voltage isn't
    regulated. There is no backward path, from the output side to the
    input, saying "I need more voltage" or "I need less voltage". The
    switching circuit is functioning open loop. The output voltage
    is higher than 5V. It then passes through the 78L05 which
    trims it to 5V exactly. And that is what provides standby power,
    power for the sticks of RAM, when the computer is sleeping.
    The 78L05 gets warm in the process, and would be one source of heat.

    The main part of the supply, has a feedback path, between secondary
    and primary. And that allows the main outputs to be used, without
    adding additional devices for regulation. The main part of the
    supply, then has a path that can say "I need more voltage". And that
    means the power supply automatically regulates as a function of the
    load. If the output voltage drops, the feedback says to pump up
    the output, to compensate. The +5VSB "secondary supply", doesn't have
    that feature. The switching stage in that one, may vary a bit,
    and the 78L05 cleans up the resulting voltage and helps it
    meet the ATX spec.

    Paul, Apr 8, 2011
  17. Puddin' Man

    Puddin' Man Guest

    These things just #bother# me, and @[email protected] me, and &bother& me ...

    The D865GVHZ board also has the little green LED, presumably for
    the same purpose. Mine are marked XY8H1 and CR8H1 on the board.

    With cpu/mem, I power up, fans spin for a second, then it shuts down.

    Without cpu/mem (or anything else), I power up, nothing happens.

    In both cases, the little green LED lights and stays lit when I apply power.
    And stays lit for about 8 secs after I switch power off. I've not removed
    the board from the case.

    So it's got the holy, holy +5VSB, and something else on the board is
    sending a shut-down message to the PS. Eh?


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 9, 2011
  18. Puddin' Man

    Paul Guest

    "Without cpu/mem (or anything else), I power up, nothing happens."

    Do you mean, you press the button on the front, the PSU fan spins,
    the system is powered ? Or it won't start at all (no PSU fan) ?

    As far as I know, all my motherboards here, start when the CPU socket
    is empty. But they could always set it up, I suppose, to not come
    on. This is Intel after all, and they could do something different.
    The VCore circuit is protected from an empty CPU socket, by virtue
    of the fact an all 1's VID code turns off the regulator.


    If you want to debug a board like that, you can look at the
    Intel reference schematic. This is the last one I'm aware of,
    that Intel issued. I haven't see one of these for any more
    modern chipsets. (25281202.pdf) Basically, this gives you some
    idea how a board can be hooked up - but the details of your
    board could be different. This one has pretty extensive "backfeed
    cut" features, that may not be present on a cheap motherboard.


    The worst part of that schematic, is it was done in Mentor graphics,
    and somebody forgot to turn on the option to make searchable text
    in the output. Mentor uses vector lettering, which can't be searched
    in Acrobat, but there is an option in Mentor, to make nicer output.
    And unfortunately, they didn't use it. Another fault with that
    reference schematic, is some of the components are phantoms. They
    should have used all commercially available components in their
    example, as a means to promoting understanding. But if you
    look at that example, you'll get some feeling for the level of
    complexity. (Document is 107 pages long.) Your board won't have an
    AGP slot, and your board only has two DIMM slots (meaning there
    would be two pages of the schematic you could ignore). I picked
    that schematic, because the Northbridge is from the same family
    as your 865. So the vintage of the schematic - it would have
    been drawn up at about the same time as your motherboard was

    PDF page 89, shows the Vcore circuit, and it's two phase (the other
    two phases are turned off). Your motherboard is also two phase
    (I see two toroids on it).

    On PDF page 79, you can see the main 20 pin power connector. PS_ON#
    comes into pin 14 of the connector. The drive for that signal,
    comes from PDF page 68, and the "Port Angeles" chip. Now, that
    might be something they use at Intel, but I have no info on it.
    So that's what I call a phantom chip. I appears to be a SuperI/O
    chip. You'd look at the SuperI/O chip on your board, and download
    a datasheet for it, to find out how it drives a PS_ON# signal.
    And so on.

    That's called "proceeding by analogy" - the Intel schematic shows
    the "general idea" and you substitute the differing details you
    see on your board. Your SuperI/O chip is just above the 20 pin
    main connector, but I can't read the part number off it. It
    might be an ITE part, but I'm not positive about that. A typical
    part number might be 8712 or 8705. Their website used to be
    iteusa.com . Typical pin count is up around 128 pins, four
    sided, rectangular shape.

    This is a sample SuperI/O. If you flip to PDF page 47, there is a
    nice diagram of how the SuperI/O drives the power supply and
    the PS_ON# signal.


    Not that any of this matters, but hey, you wanted to know :)

    Paul, Apr 9, 2011
  19. Puddin' Man

    Puddin' Man Guest

    The latter.

    I work these tests from the PSU on/off. If it doesn't start, I
    work the soft-switch. The PSU-on bought me the green LED.
    I got nothing more after working the soft-switch.
    'Twere my understanding that they usually -set- the standards, and
    don't break 'em unless setting a new one. But, anything's


    To your knowledge, if one or more of the 478 socket pins were welded
    to another during the "thermal event", we could conceivably
    see the results I've gotten?


    "Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
    Puddin' Man, Apr 9, 2011
  20. Puddin' Man

    Paul Guest

    This is an example. How many other brands of motherboard
    do it this way ?

    "BIOS Recovery Mode jumper"
    The S478 is a ZIF (zero insertion force) socket. The contacts get
    some minor protection from the plastic around the pins. VCore can
    probably provide up to 100 amps. Would the touching of two power
    pins together, result in the pin being burned off ?

    When there is no processor installed in the socket, the VID
    signals go to all 1's, the Vcore regulator is asked to put out
    zero volts. And that effectively means Vcore is switched off,
    because there'd be no gate drive on the MOSFETs. If Vcore is
    switched off, a short circuit wouldn't even be detectable.

    If an Intel designer wanted to, they could sense a single pin
    in the socket, and decide if no processor is inserted, to gate
    off PS_ON#. I don't know why you'd want to do that, but it's an
    option. All I can say, is the couple brands of motherboards
    I've got here, if you do the bare motherboard test, you can
    turn the PSU on and off. (Which is great, as a basic verification
    that the PS_ON# signal is working, coming from the motherboard.)

    At this point, you'd have to reach for the multimeter. Your first
    task, would be to set the multimeter to volts, connect the black
    lead to the chassis (I clamp onto an I/O screw with an alligator
    clip). Then, with the red lead, you'd touch PS_ON# on the main
    connector and make a voltage reading. You can jam the probe tip,
    in where the wire goes into the nylon connector body (as there
    is exposed metal in there you can touch with the probe tip).
    What you'd be looking for, is whether the PS_ON# signal is making
    good logic levels. Like, when it switches on the PSU, is PS_ON#
    dropping below 0.8V like it should ? Or does it hover around
    1.5 to 2.0 volts ? When the motherboard wants the PSU to be off,
    the PS_ON# signal should go all the way up to 5.0 volts. It could
    be that the motherboard driver of PS_ON#, isn't making good levels,
    in which case you might want to try another motherboard.

    Looking at the Intel reference schematic, they drive PS_ON#
    directly from the SuperI/O. So there really isn't much more
    probing you can do. Older motherboards (like the Intel reference
    schematic for 440BX), have a separate external chip for driving
    PS_ON#, so you can use your multimeter to probe both the
    input and output on that chip, to verify good logic signals
    are present.

    Logic levels for PS_ON# can be found in the ATX spec, an example
    of which is Figure 8 on page 27. And because the ATX power supply
    doesn't use an actual logic gate, it doesn't necessarily respond
    as shown. (If you have a signal in the undefined region, at
    least some power supplies end up in the "half-on" state, where the
    outputs work, but weakly.)


    (In the sample ATX schematic, transistor Q10 senses PS_ON#, so the
    signal isn't sensed here directly, by a logic gate. So this
    supply might do something goofy, if the PS_ON# is in the undefined



    The thing is, we can't know, just by looking at the motherboard, how many
    safety systems are wired into PS_ON#. An obvious choice is THERMTRIP,
    and all motherboards should be using that now. If the processor
    sends THERMTRIP, the power should go off immediately. But many other
    things could potentially be included, such as an overcurrent signal
    coming from VCore.

    In some cases, the inclusion of some of these safety features, results
    in unnecessary product returns to retailers. You really only want
    the safety feature to trigger, when a serious fault is happening.
    Nuisance trips, won't win you any friends.

    Paul, Apr 10, 2011
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