Joe said:
On Saturday 11-21-09 my home built 4 yr old computer just quit. XP Pro SP2,
retail version, K7S5A motherboard, ATI Radeon graphics card. Reset computer
and it came back on. 4 hrs later, same thing. Tried to restart but but this
time no screen, no optical mouse led light. Monitor says no signal. Does not
get to BIOS screen or anything. Just a black screen. I can hear hard drive
start. Here's what I have done-
1. Removed HD and put it in another computer. Boots ok. All files there.
2. Put in a old but good NVIDIA graphics card. Still no screen.
3. Put in old but good 512 memory stick. No luck. Worth a shot.
4. Took power supply to tech shop to test. Ok.
5. Changed ribbon cable.
Any other suggestions? New Board?
One debugging technique for motherboards, is to use the computer case
speaker and the "beep codes". With the power off on the power supply,
remove all the RAM and the video card. (Store them in antistatic bags,
until it is time to reinstall them.) The BIOS should normally notice
the RAM and/or video is missing, and give a beep pattern. Beeps are used
for any error condition that cannot be printed on the screen.
If you hear a beep pattern at startup, with the components missing,
you know the processor is getting power, and the path through the
Northbridge and Southbridge works. (The processor makes the beeps - a
dead processor, and no beeps.) I'm assuming the case speaker is
connected to the SuperI/O chip, which is connected to the Southbridge.
So to get there, and do the beeping, requires a lot of working
hardware.
If you're not getting any beeping, it could be a bad processor,
broken Vcore regulator, problem with chipset (processor can't fetch
BIOS code, as that flows through the chipset too). I suppose, even
the case speaker could be broken, but we shouldn't think about a
second failure at this point. We know something else is busted,
and that is most likely to prevent the speaker from beeping.
Some motherboards have a round black piezo speaker mounted on the
motherboard itself. That might be more common on pre-built systems
or maybe on a server. Retail motherboards like yours, should really
have a couple SPKR pins on the PANEL header, to connect a case
speaker to. If you haven't connected a case speaker, you're not
going to hear any beeps. So check your speaker situation, and if
the speaker looks like it is installed properly, remove the
video and RAM and see what response you get. If you do get some
beep pattern, add back the RAM. If the beep pattern changes with
the RAM back in, you might conclude the RAM is recognized a bit.
If you plug in the video and the beeping stops, then you'd suspect
the video is holding the system hostage (like a bad AGP slot).
If it beeps the same as the last test case, then maybe the video card
is bad.
In other words, if you think about it, each test case has two outcomes,
and the beep pattern or lack of beep pattern or different beep pattern etc,
is telling you something. It is like a fault tree, where each test case
takes you down a different branch of the tree.
If you failed the very first test case (i.e. remove RAM and video), and
there are no beeps, it could be a bad processor. You'll need to remove
the heatsink and have a look. Some AMD processors "cook" under there,
and if you see severe discoloration, a large crack or the like, you
have your answer. If not, clean of the dried paste, and apply
a thin coat of fresh stuff, before reinstalling the CPU heatsink.
Be careful not to crack the silicon die (a shim or four rubber bumps
helps prevent tilting of the heatsink and a cracked edge on the die).
You can do simple visual checks for the motherboard, like look for
bulging caps. I don't know what the reputation is for your mobo,
with respect to caps. Caps have stress relief cuts on the top,
so that the cap won't explode. If there is bad mojo (chemistry failure)
inside the cap, the top bulges, the pressure is relieved and the
goo leaks out. It can eat stuff it touches, or discolor things.
A skilled hobbyist can replace the caps, assuming you buy a cap
kit somewhere, from someone who knows how to select good quality
replacements. Pulling the caps out of the board, without ruining
something, takes good tools (and practice on a board you don't
care about). Considering the age of your motherboard, it might
be hard to find a decent substitute. Depends on the whims of Ebay.
http://en.wikipedia.org/wiki/Capacitor_plague
Since you've had your power supply tested, we can assume it is
OK. It should have been tested under a light to moderate load,
rather than just being switched on and listen for the fan
turning.
Paul
