Wyman said:
Hello -
I'm trying to help a friend resolve an issue with her computer. The
computer boots up, I hear and see the CPU/video fans spinning, the power
supply is working, and the hard drives are running. There is a lit LED on
the front of the computer also. I've tried several monitors on the onboard
monitor port and get no single and I've also tried 4 different video cards
which are from working machines and still no video. I have no idea what
could be the problem. Could it be the motherboard?
The operating system is XP Media Center, 2.4 ghz AMD cpu, 200gb hd, and
512mb ram. If you need more please me know.
Thanks,
Wy
When there is no signal coming to the monitor, concentrate on
"beep testing".
Most computers will have an audible output, used for error conditions.
This is independent of the normal computer sound system. Some computers
use a speaker which is part of the computer case. Others use a piezoelectric
device, coin sized and 3/8" tall or so, and that is used to generate
a "PC beep".
http://www.norcalqrp.org/kits/NCKeyer/elmer/P7190026a.jpg
One test you can try, is remove the RAM, and listen for the beeps.
The computer should be completely powered off, when you remove the
RAM. The RAM should be carefully stored in an antistatic bag, while
you're doing the test. The RAM uses a slot&key approach, to enforce
correct insertion, so take note of the orientation during removal.
If there are two sticks, remove both of them. Note which slots
you found them in.
The PC should emit a beep pattern, if the RAM is missing. If you hear
the beep, it tells you the processor is running (because the processor
programs the beep in hardware). If you don't hear a beep, then the
processor, motherboard, or power supply are at fault. The BIOS chip
on the motherboard, contains code that would be used by the BIOS,
so even a corrupted BIOS chip could be the source of a problem.
The addition or removal of the video card, is also covered by its
own beep code. But that isn't always a good test, because there
will be a fair number of computers with integrated (chipset) video,
and you can't "remove" that for testing. On computers with a
separate video card, and no built-in video, that would be a
second test case to try. You'd have the RAM installed, and the
video removed, and again be looking for a response. If there
were no beeps, then the RAM could be bad (causing a failure to
POST). If there is a beep pattern, and the beep pattern is different
than the other beep pattern, then the RAM test could be passing
(and the beeps for video are to be expected).
Some Dell computers have a four LED diagnostic display, and it gives
more details about failures. A limited set of years of Asus motherboards,
had their own audio subsystem, which gave audio messages about the
possible failure cause. That added about $1 to the product cost, but
may have occasionally helped.
You can get one of these cards, a PCI diagnostic card. It works, by decoding
writes to port 80 in I/O space. You plug the card into the PCI slot nearest
the processor. Start the computer, and a two digit hex display outputs
codes. The BIOS has the codes embedded in it, and writes "progress" codes
to the display, as the power on self test code is running. The main value
of such a display, is it shows 0x00 or 0xFF if there is no POST activity
at all. That tells you the processor is not running. For any of the other
codes displayed, I've yet to run into a case, where seeing a code, leads
to a diagnosis. So in that sense, these aren't particularly a good investment.
But if you saw the display changing values rapidly, then get stuck, it
means the BIOS ran into a problem, part way along the POST testing.
There are tables of codes available, for the various brands of BIOS.
http://www.newegg.com/Product/Product.aspx?Item=N82E16815158065
Something else you can try, is Google "Gateway 816GM", and look for
what high runner faults exist for the model.
Another condition to check for, is bulging or leaking capacitors. Some
Dell computers, for example, had an epidemic of this. So bad in fact, that
if you were buying a used motherboard for such a computer, chances are the
replacements would also be in bad shape. The capacitors age prematurely.
(I had a power supply here, fail because of this, and it had very few
service hours on it.) Bad capacitors around the CPU socket, can rob the
CPU of a stable power source. And that would match your current symptoms.
The beep tests may give you a little more evidence to go on.
http://en.wikipedia.org/wiki/Capacitor_plague
Post back, with any new symptoms from your tests, as to whether you got
any beeps or not. Or for that matter, whether the computer has an
audible "PC beep" device in the computer case.
*******
OK, I can think of another reason for it to not POST. And that would be
because of a bad CMOS battery. But then, if that was the case, the
user would note the "time is not right when I start the computer". So
there would have been other symptoms presenting themselves, just
before this incident. The CR2032 is very popular on modern systems.
It should read 3.0V or so, when still good. Below 2.4V, it is dying and
needs to be replaced. 2.4V, minus a diode drop in the battery path,
leaves 2V to power the CMOS RAM and real time clock. And it stops
working below 2V or so.
http://www.p4c.philips.com/files/c/cr2032_01b/cr2032_01b__fg_.jpg
You can check the battery voltage, without removing the battery. Connect
the black lead of a multimeter to a shiny screw on the back of the computer.
That is your "ground" connection. Connect the red lead to the top of the
shiny coin cell battery. The top is relatively large, so you should be
able to measure it easily. The test leads on the meter should be in
the "volt holes". The meter should be set to a range slightly higher
than the battery voltage (10 volts DC full scale or 20 volts DC full scale).
If your reading is dipping below 3.0V, then think about picking up a
replacement.
On some computers, there are a significant number of custom BIOS settings
that can be lost, when the battery is removed. But in a case where you
can't get a computer to POST, you don't have much choice in the matter.
You put in the new battery, then correct the BIOS settings as best you
can. For example, on a Vista computer, the disk interface may be in
AHCI mode. A WinXP computer may have been set up with a "vanilla IDE"
setting for the disk interface. So on some computers, the loss of the
battery and CMOS settings, may require some experiments, before
the computer will boot properly again. The setting needs to match what
was previously there, because of the driver used to interface to
the disk.
And when working in the computer, like removing the battery,
it is best if the computer is completely powered off. I like to
use a wrist strap for things like RAM, to give a bit of antistatic
protection. A wrist strap keeps your body at the same electrostatic
potential as the chassis, and subjects the hardware to fewer
jolts while you're working. But if you don't have a wrist strap,
you can fake it, by holding onto the chassis when adding or removing
the hardware. That second hand, can also be holding the antistatic
bag you use, to temporarily store the removed hardware.
Wrist strap (clip to a screw on the case).
http://www.radioshack.com/product/index.jsp?productId=2103808
Good luck,
Paul
