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Replaced motherboard on HP machine

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November 19, 2010 4:45:51 AM

I have an HP a375c computer running XP which wouldn't start up after a power outage. The light on the back of the PC was flashing, which some say indicates the motherboard has failed, if it continues to flash when all other power devices are disconnected. Put in a new board (DM17069001), repopulated with cpu and memory and the light still flashed. Read that the light indication was not reliable, and could be a power supply issue.
Tried a new PS, without the cpu, and memory. The power supply fan started up, the front panel power button lit up, and both fan and light went off after a fraction of a second.
Anyone have any insights on this issue. I had assumed the circuitry on the motherboard doesn't need the cpu and memory to be installed to keep the power supply on, but could see the possibility that they're required. Any ideas on how to isolate where the problem exists. The system is used in a business to run custom data acquisition software running in Dos, so upgrading to a Windows 7 machine won't be feasible.
Any help would be appreciated

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a b V Motherboard
November 19, 2010 5:40:58 AM
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You need ram and a cpu in there or it wont fire up, try the new psu with the board set up correctly,
check section three for some tips too http://www.tomshardware.co.uk/forum/288241-13-read-post...
and dont forget Win7 could possibly be an option, http://www.microsoft.com/windows/virtual-pc/download.as...
hope this helps,
Moto
a c 156 V Motherboard
November 19, 2010 1:47:30 PM

Work through our standard checklist and troubleshooting thread (the one moto linked to):
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:
http://www.cwc-group.com/casp.html

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU.

Motherboard LED's mean very little. When on, all they are telling you is that the computer os plugged into a live power socket and the PSU is switched.

Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
Related resources
November 19, 2010 1:58:47 PM

Motopsychojdn said:
You need ram and a cpu in there or it wont fire up, try the new psu with the board set up correctly,
check section three for some tips too http://www.tomshardware.co.uk/forum/288241-13-read-post...
and dont forget Win7 could possibly be an option, http://www.microsoft.com/windows/virtual-pc/download.as...
hope this helps,
Moto

Thanks for the links and info - will follow the trouble shooting section.
Do you know if the Win7 solution would support a Dos program using the RS 232c communication port?

Michael
a b V Motherboard
November 19, 2010 2:07:43 PM

None too sure to be honest,
I've only been building a year myself and I prefer hardware issues to software ones hehe
but I just thought the emulator may hold the solution for you if theres some restriction for the program running on Win7,
I would assume it 'should' run fine on it though thats the point of an emulator right?
Moto
November 19, 2010 3:27:28 PM

jsc said:
Work through our standard checklist and troubleshooting thread (the one moto linked to):
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

I printed out the troubleshooting section, and will have it right at the pc. Thanks for the additional guidance.
Michael
November 29, 2010 1:23:53 AM

Motopsychojdn said:
You need ram and a cpu in there or it wont fire up, try the new psu with the board set up correctly,
check section three for some tips too http://www.tomshardware.co.uk/forum/288241-13-read-post...
and dont forget Win7 could possibly be an option, http://www.microsoft.com/windows/virtual-pc/download.as...
hope this helps,
Moto

I followed the guideline link that JSC provided, and added the cpu and ram, and it started right up (with new power supply). Problem was most likely just the power supply, but didn't try the old MB.
Thanks to all for the guidance
November 29, 2010 1:24:19 AM

Best answer selected by Michael_C.
a b V Motherboard
November 29, 2010 5:33:53 AM

Thank you for B.a., glad you got sorted ok :) 
Moto
a c 135 V Motherboard
November 29, 2010 5:37:57 AM

This topic has been closed by Maziar
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