Question Core 2 Duo replacement problem

Jul 29, 2019
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I have an HP-Compaq small format desktop PC that has a 1.8 GHz Core 2 Duo in LGA775 package.
I tried to replace it with a 3.0 GHZ Core 2 Duo ( I think it's an E8400 ). After replacement, I replugged
the power cord and turned on the PC. The machine bleeped and the power LED blinked red thrice,
then the power supply disabled itself. I put back the old CPU, but now the PC also bleeps and the
power LED blinks red when I turn it on, with the difference that the fans and DVD drive continue
to operate, and the bleeping and blinking stops for a while, then repeats.
This seems an overload problem, but the PC worked before I attempted that replacement
and I have seen machines of the same model using up to 3.3 GHZ Core 2 Duo CPUS.
Could it be that the new CPU was bad and burned some onboard voltage regulator ?
Does anyone have some repair advice ?
 
Let's try some basic troubleshooting:

Reset the BIOS - with the system unplugged from the wall locate a small coin cell battery and release it by depressing the retention clip holding it in. Wait a minute or two than replace it and try to boot again

Reset the RAM - again, unplug the system to avoid accidental damage. Remove each memory stick until the slots are all empty than re-install them.
 
Jul 29, 2019
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I did as you ask. At first try, the power LED would stay green, but the PC would'n boot
- no video, no disk activity.

I performed several times the routine of removing then replacing the CPU with the
power cord unplugged and the coin cell removed, then replacing the cell and found
three outcomes :

5V aux LED lits green on plugging the cord, at turn on the power LED blinks red
and the loudspeaker beeps. The power cannot be turned off by the power button.

5V aux LED lits green on plugging the cord, the power turns on by itself after a few
seconds, the power LED lits and stays green, the fans run but there is neither video
nor disk activity. The power cannot be turned off by the power button.

5V aux LED lits green on plugging the cord, when the power is turned on by the
power button, the power LED lits and stays green, the fans run but there is neither
video nor disk activity. The power can be turned off by the power button.

The difference between the old (E6300) CPU and the new (E8400) is that with
the former the red blinking stops, then restarts after a few seconds, while with
the later the red blinking does not stop.

This is the same whether or not the CPU heatsink is in place. (Those tests last
but a few seconds, so the CPU does not heat enough to hurt when I touch it).
 
You're most likely looking at a bad motherboard then. The last troubleshooting steps would be unplugging every non-essential device from the board (leave power button and power supply but disconnect SATA, USB, Audio panel). Leave a monitor connection but no other external peripherals. If any add-on cards are installed remove them.

If you want to move ahead with this PC, the HP board number usually has the form XXXXXX-XXX found on a sticker somewhere. Ebay should have one somewhere, likely used (of course this hasn't been made for some years). If your budget allows, consider something even like a refurbished system of somewhat newer vintage.
 

lynx1021

Reputable
Feb 17, 2016
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Like SchizTech said we really need to know the model number of the HP and motherboard. I remember some of the early model Core 2 duo machines could not use the later Core duo CPU's like the E8400, It had to be a Conroe processor where the E8400 is a Wolfdale. Check for bent pins in the socket. A friend of mine tried changing his CPU with the board vertical in the tower and bent some pins. I saw where one guy recommended using a mechanical pencil with no lead to straighten pins. I have two 775 board still going!
 

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