Check for shorts on all the power rails, then check for shorts from the 12V processor supply to the VRM coils. Then check for shorts from all the coils on the motherboard to ground.
Have a look at any of the videos from Daniel here https://www.youtube.com/@mainboardmedic as he always starts with those basic checks.

I have a P5Q, which is very similar. Fortunately mine is working fine.

Great insight. I will do that and put back the results.
Thank you.

Check if the vcore pwm ic is getting the enable signal, it should be at least 0.8v.
I have marked the resistor leg where you can measure the enable signal.
also check the 1.8v and 1.1v coils, without these 2 main rails there wont be vcore.

The results for the resistance checks on the power rail are: 3.3V=90Ω; 5V=720Ω; 5VSB=2kΩ; 12V=~12kΩ. The value for 3.3 and 5V seems low...
The coils are good, except for the 1.1V coil on the picture uploaded by Karbist. There is 0Ω on this coil and it is effectively shorted.
The 0.8V resistor was measured at 0V (I've retried multiple times because the resistor is hard to see).
I've also tested the 1.1V and 1.5V MOSFET's and they are good.

So, I should change this coil, right?

coil is a bundle of wire, its supposed to be shorted 😀
besides Karbist asked you to measuere voltage on those coils
sadly boardview doesnt seem to be available for ASUS P5Q-EM, 10 or so other ASUS P5Q variants are but sadly vastly different power circuits

I've remade all the measurement with a CPU and I've noted all voltage on the picture "p5k-em_voltage.jpg" below. I hope it's clearer that way.
The voltages on MOSFETs was taken on the source pins.

About the coils, I was doing what EduBat suggested when I should "check for shorts from all the coils on the motherboard to ground".
The resistance checks on the coils are highly inconsistent or I'm doing something wrong.

rasz_pl wrote on 2026-10-03, 20:11:

sadly boardview doesnt seem to be available for ASUS P5Q-EM, 10 or so other ASUS P5Q variants are but sadly vastly different power circuits

I think P5Q-EM is the same as P5Q-VM but with added HDMI + SPDIF ports and added IE1394 chip and pin header.

there are 2 mosfets in parallel between the 1.1v coil and ground, check the resistance between the gate leg of mosfet and ground, it should be in kilo ohm range.

if the 1.1v coil is shorted to ground, it could be a dead north bridge chip, although I had a board that the tiny capacitor on the chipset was shorted.

attached boardview:

I checked the resistance of the MOSFET between the gate and ground, where your red arrow is, and it says 8.1 kΩ.
The MOSFET just to the left have the same reading.
The MOSFET just to the left and below have 0Ω though.

The next step is to find where the 1.1v rail is shorted to ground, that usually is done by injecting 1 volt to the shorted rail and looking through the thermal camera to see what component gets hot.

Thank you very much Karbist for your help.
I don't have the tools to do this right now but I'll see what I can do...

Pikes6 wrote on 2026-10-04, 07:57:

rasz_pl wrote on 2026-10-03, 20:11:

sadly boardview doesnt seem to be available for ASUS P5Q-EM, 10 or so other ASUS P5Q variants are but sadly vastly different power circuits

I think P5Q-EM is the same as P5Q-VM

1dir *p5q*
2
310/08/2020  19:46           131,038 ASUS P5Q REV 1.03G 60-MIB4P0-B0A (BOARDVIEW).rar
410/08/2020  19:51           145,757 ASUS P5Q-E REV 1.01G (BOARDVIEW).rar
501/09/2023  15:38           150,697 ASUS P5Q3 DELUXE 1.02 B1A.rar
610/08/2020  19:55           102,920 ASUS P5QL PRO REV 1.00G (BOARDVIEW).rar
710/08/2020  19:45           103,801 ASUS P5QL REV 2.01G (BOARDVIEW).rar
810/08/2020  19:49           105,185 ASUS P5QL SE REV 1.01G (BOARDVIEW).rar
910/08/2020  19:52            96,156 ASUS P5QL-I SI REV 1.04G (BOARDVIEW).rar
1010/08/2020  19:47           111,653 ASUS P5QL-M EPU DP REV 1.01G (BOARDVIEW).rar
1111/08/2020  08:45            97,760 ASUS P5QPL-AM  REV. 1.04G (BOARDVIEW).rar
1228/02/2024  08:36            98,290 ASUS P5QPL-AM REV 1.03G (BOARDVIEW).7z
1310/08/2020  19:45            97,758 ASUS P5QPL-AM REV 1.04G (BOARDVIEW).rar
1410/08/2020  19:48           107,430 ASUS P5QPL-VM EPU 1.01 A01 (BOARDVIEW).rar
15              12 File(s)      1,348,445 bytes
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> "I was doing what EduBat suggested when I should "check for shorts from all the coils on the motherboard to ground"

Sorry if I didnt sound helpful, I should have quoted the line I was replying to directly, this "There is 0Ω on this coil and it is effectively shorted" "So, I should change this coil, right?" to be exact. Coil is either shorted and working or blown/open and not working. Coil is never the direct cause of shorted rail.

Might be shorted lower mosfet, might be shorted mosfet driver, might be something powered by 1.1V line.
~easiest way to quickly determine where the problem lies is desoldering (will require powerful soldering iron) this coil and checking which side has the short, regulator or load

You could also check if the crystal die of the northbridge isn't cracked/damaged. If the die is damaged it can cause a short.