ASRock Z68 Extreme 4 can't boot

[senderj]

Re: ASRock Z68 Extreme 4 can't boot

PWM controller is CHL8328 (data sheet attached) and driver for the gates is CHL8510 (data sheet in #19)

[senderj]

Re: ASRock Z68 Extreme 4 can't boot

To sum up, my last finding was that after every power up, there is a varying resistance between G and S of the upper mosfet which changes from 3 ohm to open (or rather 8K6 due to a resistor between them) in a very long time (>10 hrs). This almost-shorted G-S makes reboot fail (Vcore=0V). I cannot proceed any further from here.

However, I did try to figure out the schematic of the VRM and draw it up here. All component values are DMM reading, so it may be the result of a problem on the board rather than actual component values. Among which I found something near the lower mosfet that I don't understand since I don't have the fundamental knowledge. It may be a problem or just my ignorance. When DMM at 200ohm selector, the reading between A & B (yes, it's the cap) is 95.9 ohm while between A & Gnd is 94.8, lower than AB. And all 8 VRMs are consistent. How can it be lower? Does it means something wrong with the driver IC? All 8 of them?

[momaka]

Re: ASRock Z68 Extreme 4 can't boot

Sorry for not replying yet. I just moved back to university and have no internet. Currently using the library's computers. Should get internet back in a few days hopefully.

[senderj]

Re: ASRock Z68 Extreme 4 can't boot

While I have some low resistance in G-S of upper mosfet of Vcore after power off, I later observed the same thing in Vdisplay and Vtt. So this may not be a problem I guess.

But I also have new findings. This time I tested and repeated it 5 times to make sure it is related to my problem. When the board operate normally (i.e. cpu fan turning, diagnostic LED on, beep sound, UEFI working), Vcore is 1.03V with 2 of 8 phases' mosfet gate have voltage, Vdisplay is 0V with gates also 0V (UEFI doesn't use CPU display is something new to me). When it fail (i.e. cpu fan turning, no diagnostic LED, no beep, no UEFI at all), Vcore is 0V with all gates 0V, Vdisplay is 0.92V with gate voltage. The failure and above voltage changes happened at the same time and repeated in all 5 tests. Can somebody please tell me if this can help locate the problem on the board?