pre bios failure

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I have a machine that when powered on the fans spin, a light on the
mobo shines and the keyboard lights pulse.   The machine is a Dell
GX270 and has the  4 LED diagnostic indicator lights on the IO
pannel.   They are all dark.   Previously this machine could only be
encouraged to boot by unplugging the power supply, waiting for the
board to discharge electricity (~45 seconds), then plugging it back in
and pressing the start button.   The power supply was checked with
some 20-pin tester - all lines appeared to be providing the proper
power.   So, my next tests would be to pull unnecessary boards, reseat
existing memory and necessary boards, possibly pull the board to avoid
any grounding issues .....  but beyond these measures does anyone have
other diagnostic checks?      Why's the keyboard flashing?    Is
anything indicated by the discharge/boot thing?

Re: pre bios failure

On Wed, 16 Jan 2008 07:42:18 -0800 (PST), Johnny Ruin

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Has the system been changed or upgraded beyond it's initial
factory config?

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Unfortunately, the typical plug-in tester can only find
certain kinds of PSU faults, not all faults and it can't be
used to determine a PSU works properly powering the load
(system).  A bit better test would be using a multimeter to
measure voltage levels of the PS-On, Power-Good, 5VSB, 3.3V,
5V, and 12V rails before, during, and after the power button
is pressed (3.3V, 5V, and 12V need only be measured after
it's pressed).

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yes, disconnect everything but one memory module, video
card, CPU, heatsink/fan.  Some boads won't POST with one
module if they'd been running with two but a CMOS clear
should allow othat, or just try it with 2 modules installed
initially.  Disconnect even the keyboard and other
periperals, only caring about getting it to POST.

Unless the board were improperly mounted in the first place,
it is not likely to suddenly develop grounding or shorting
out problems... unless a wire somewhere had broken off and
is now shorting but it won't be necessary to pull the board
to determine this.

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Is keyboard continually flashing or just flashing once?
Once is normal.  Check the motherboard capacitors for signs
of failure, domed or vented tops or residue from leakage on
tops or bottoms.

If the motherboard caps look ok the odds shift to it being a
PSU problem.  Also check things like the video card fan if
so equipped, a seized fan could point to a heat stressed ->
damaged video card.

Re: pre bios failure

Hi Kony,

Thanks for the elaborate response!   The system did have a second hard
drive put in recently.   The keyboard flashes continuously - that is,
blinking off/on without ceasing.     A quick inspection of the
capacitors  didn't reveal anything suspect (but thanks for the tip - I
didn't know that was something to check).
 I haven't tried the power supply the tests you suggested yet.   I'm
hoping to get to that this weekend.    But after that and the re-
seating/CMOS clear stunts I guess that's pretty much the end of the
diagnostic road.    Thanks again for your response - after I go
through these last things, if it's still a dead machine I'll at know
I've given it a pretty good shot.

Re: pre bios failure

Johnny Ruin wrote:
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