Broken PC - wits end

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Hi - Hope someone can help. About 6 weeks ago my pc stopped booting.
Believing that my motherboard was blown (was a socket A AMD and hard to
find replacements) I bought a new MB and chip - Foxconn 760GXK8MC-S
Motherboard + Sempron 2600 chip. Fitted everything - same problem.
Checked the power supply with a meter - all voltages seem correct. So
replaced the RAM with a 128 MB DDR PC2100 (not because I want that
little memory, but am running out of money). Still no boot.

The hard disks do not seem to be spinning up, the CPU fan is running,
and lights come on on the USB mouse when plugged in, and also on the cd
drive. The monitor does work - I have tested that on my laptop
(courtesy of my employer).

So - any suggestions?

Re: Broken PC - wits end

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Simplify the system and work your way up. Unplug the computer
before adding or removing components, to avoid damaging anything.
(Unplugging means there is no way the +5VSB can be on.)

Asus motherboards equipped with Vocal POST, can actually deliver
an error message without any components installed to the motherboard.

At the next level, are motherboards that use beep codes (or perhaps
have display devices, like a POST code display). On those, a processor
(and a BIOS flash chip with good code in it) plus your power supply
and the computer speaker, is enough to get a beep code. If the beep
code says "the RAM is missing", you know the processor was able to
execute some of the BIOS code. To make the beep sound, the processor
programs the super I/O chip, in order to get the speaker
to beep. The code run by the processor, uses registers for
temporary storage, so no RAM is needed to execute the code.

So, given this is a Foxconn board, I would take the motherboard,
processor + HSF, a computer speaker that plugs to the PANEL header
or equivalent on the motherboard, an ATX PSU and connect them together.
You don't need to plug a lot of crap to the PANEL header to
get the motherboard to run - touching a screwdriver tip to the
two pins where normally the "power" switch from the case would
go, will start the motherboard up. The pins are momentary
contact. Once an experiment is finished, switch off via the switch
on the PSU (easier than using the screwdriver a second time).
(This assumes the two power pins are adjacent to one another
on the panel header. If the pins were spaced far apart, a
screwdriver would be useless, and the power switch on the
case should be used instead.)

I use a phone book with a paper/cardboard cover, as a base for
the motherboard when bench testing. The added height allows the
faceplate tab some room, where it hangs below the plane of the
motherboard. The cardboard is an insulator, so won't short the
underside of the board. When inserting components that require
insertion force, you want something to support the motherboard
and prevent it from being flexed. (Flexing surface mount
components can break the solder joints, if you do it enough.)

If that simple test passes, add components one at a time on your
benchtop. If you get to the level of inserting a video card,
be very careful not to tug on the monitor cable while the
video card is sitting unsupported in the slot. If you partially
pull it out by accident, it could be destroyed. (If you have
pets, this means a locked door, and a no-pet policy while

Some users happen to leave brass standoffs in the motherboard
tray, where they are no longer needed. If the motherboard
has nine plated holes in it, you install nine standoffs.
Check that a standoff is not touching a part of the board
where there is no mounting hole.

That should be enough to get you started.

If you cannot even get the CPU fan to spin, then the power
supply would be your first suspect. But since you've mentioned
that stuff is spinning, there is hope yet.


Re: Broken PC - wits end

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If the HDs don't spin up, I suspect you have a power supply problem or a
problem with the connections to the HD.  You said you checked the power
supply voltages.  Is there +12V at the HD?  I think the HD should spin up
with only the HD connected to the power supply.  Sometimes putting a data
cable on backwards can make drives appear to be dead.  I presume you've
checked that.


Re: Broken PC - wits end


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Describe the rest of the system, concise list of all majory
components.  Next, what make and model power supply and it's

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Unplug all drives from both power and data cables.
Then try to turn on the system.  If it works, add back each
drive one at a time, first trying it with only the power
cable connected to see if it spins up.  If/when you find a
drive that appears to be a problem, connect only that drive
(power cable only, not data), note whether it spins up, and
measure voltage at the power connector.

If voltage significantly changes with drive hooked up and
it's not spinning, the drive is probably faulty. You could
also disconnect all components from the PSU, having only the
questionable drives hooked up and turn on the PSU by
shorting the Pin 14 on the ATX 20 pin connector to Gnd (any
black wire) with a metallic object such as a small gauge
paperclip, at which point the drive should spin and voltage
readings can again be taken.

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Just take it step-by-step, removing all parts and adding
them back one at a time between each attempt.  Also clear
the motherboard CMOS while AC power is disconnected.
Initial impression is that it's probably one of the drives
or the power supply.

Re: Broken PC - wits end

AlanB wrote:

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The lights of the USB mouse and CD drive often mean the +5V is OK.  As
for the +12V, unplug the data cables to the hard drives, and if that
lets them spin, then very likely the +12V output is all right as well.
Otherwise I suspect it's low since fans can spin even with the +12V
output being as low as about 6V.  Did you attach power cables to every
power connector on the motherboard?  How did you test the power supply?
 I ask because readings taken without realistic loads can hide
problems, such as marginal filter capacitors. I also hope you're not
using an Antec NeoHE power supply, which has been found to be
incompatible with some motherboards and has reportedly even damage them
or their peripherals.  By the way, it's safer to test a system by
installing only enough parts to safely operate it (such as the CPU
heatsink and fan) and see signs of life, meaning leave the disk drives
disconnected form their data and power cables.

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