stumped! will not go through BIOS sequence

  • Thread starter Thread starter Neal McEwen
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Neal McEwen

I have been trying to fix my son's PC. It is like the monitor does not
see the computer. When you turn on a computer, it normally goes thru
the BIOS sequence and shows you what it is doing on the monitor. This
PC does not even do that.
The first thing I tried was a new video card -- no luck.
Then I tried a new motherboard -- no luck.
The BIOS is on the motherboard, so if the mother board and video card
are new, what is left?
I measured all the voltages on the ATX connector from the power supply
while plugged into the motherboard. They all measure about 30% high on
a DVM. Is this indicative?
We unplugged all the ribbon cables, thinking something else was dragging
down the MB -- no luck.
I don't think it could be the CPU, because even without a CPU or with a
bum CPU should'nt it still go thru the BIOS sequence?
I am open for suggestions. Can anyone give me some fresh ideas?
Thanks for any help!
 
They all measure about 30% high on
a DVM. Is this indicative?

that's indicative,,,,5% is allowable but 30 is a out of line. can't
say that its THE cause of your problems but after a MB swap that only
thing really left is the power supply.
 
you have the speaker hooked up? no beeps?

JAD said:
They all measure about 30% high on
a DVM. Is this indicative?

that's indicative,,,,5% is allowable but 30 is a out of line. can't
say that its THE cause of your problems but after a MB swap that only
thing really left is the power supply.




does high
Click to expand...
 
Neal said:
I have been trying to fix my son's PC. It is like the monitor does not
see the computer. When you turn on a computer, it normally goes thru
the BIOS sequence and shows you what it is doing on the monitor. This
PC does not even do that.
The first thing I tried was a new video card -- no luck.
Then I tried a new motherboard -- no luck.
The BIOS is on the motherboard, so if the mother board and video card
are new, what is left?
I measured all the voltages on the ATX connector from the power supply
while plugged into the motherboard. They all measure about 30% high on
a DVM. Is this indicative?
Click to expand...

Well, it's indicative that SOMEthing is wrong because 30% is WAY out of spec.
We unplugged all the ribbon cables, thinking something else was dragging
down the MB -- no luck.
I don't think it could be the CPU, because even without a CPU or with a
bum CPU should'nt it still go thru the BIOS sequence?
Click to expand...

No. There's nothing to 'run' the BIOS without a CPU.
 
Neal McEwen said:
I have been trying to fix my son's PC. It is like the monitor does not see
the computer. When you turn on a computer, it normally goes thru the BIOS
sequence and shows you what it is doing on the monitor. This PC does not
even do that.
The first thing I tried was a new video card -- no luck.
Then I tried a new motherboard -- no luck.
The BIOS is on the motherboard, so if the mother board and video card are
new, what is left?
I measured all the voltages on the ATX connector from the power supply
while plugged into the motherboard. They all measure about 30% high on a
DVM. Is this indicative?
We unplugged all the ribbon cables, thinking something else was dragging
down the MB -- no luck.
I don't think it could be the CPU, because even without a CPU or with a
bum CPU should'nt it still go thru the BIOS sequence?
I am open for suggestions. Can anyone give me some fresh ideas?
Thanks for any help!
Click to expand...

Do you know that your DVM is OK? To me, your post points to several
symptoms. 30% is way too high for voltage readings. BUT, if your power
supply was bad, it is somewhat unlikely that it would be bad in a way that
your DC voltages would all be about 30% too high. That's why I'm wondering
about the accuracy of your DVM. If your output voltages really ARE 30% too
high, then your CPU is not reading "good" voltage, and thus it will not run
POST. So the simple fix would be to replace the power supply, and hope that
those sky-high voltages did not damage anything else.

For future reference, your computer does (roughly) the following when you
turn it on.
- First, the CPU is looking for a good power signal. Thus, your power
supply has to be OK.
- When CPU sees power good, it starts running POST program stored in BIOS.
(thus your power supply and CPU need to be OK)
- During POST, the video card might eventually be initialized, if the
hardware passes certain very basic checks first.
- If the video card can be initialized, then you will get video on your
monitor, showing RAM being tested and other components being initialized.
- Final step is for the CPU to look for an OS to boot, according to the
boot sequence that is stored in CMOS.

Of those five steps, you have a system that is stuck somewhere in step one
or two. I suspect a bad power supply. But even if I'm right on that, a bad
power supply can lead to other problems. A bad motherboard or bad CPU could
stop the process in step one or two, also. As you've already tried a new
motherboard, you are probably looking at a bad power supply or bad CPU, with
power supply as most likely suspect. -Dave
 
OK, thanks much for all the help from each of you that responded.
to answer the questions.
1. I see the leds light up on the keyboard for an instant, so something
is talking to the keyboard.
2. There is no beep from the speaker and I have it hooked up.
3. I just put the DVM accross a new duracell AA and it read 1.60 volts
-- looks like the DVM is that that far off.
If all the voltage read 30% high will the CPU/MB shut down or has
the PS fried both of them?
I have an old case from a Pentium I machine -- I'll look at the PS
to see if the pins and voltages are the same.
Once again, thanks for the help.
 
Neal McEwen said:
OK, thanks much for all the help from each of you that responded.
to answer the questions.
1. I see the leds light up on the keyboard for an instant, so something
is talking to the keyboard.
2. There is no beep from the speaker and I have it hooked up.
3. I just put the DVM accross a new duracell AA and it read 1.60 volts --
looks like the DVM is that that far off.
If all the voltage read 30% high will the CPU/MB shut down or has the
PS fried both of them?
I have an old case from a Pentium I machine -- I'll look at the PS to
see if the pins and voltages are the same.
Once again, thanks for the help.
Click to expand...

Actually, a new AA should read about 1.6 volts. So it looks like your power
supply is WAY off. Voltage that high could damage a CPU or certain
motherboard components, but hopefully that hasn't happened. First thing to
do is replace the power supply. If that doesn't help, maybe the CPU is bad.
But if the power supply is really 30% high (seems that way), then you know
for certain that the power supply is definitely bad. Start with what you
know, and work from there. Replace the power supply. -Dave
 
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