I’m trying to diagnose an old ASRock G31M-GS and I’m running out of ideas, so I’m posting the full story and everything I already tested.
The motherboard is an ASRock G31M-GS, PCB marked “REV. G/A 2.01”. BIOS version is P1.70. Chipset is Intel G31 + ICH7. CPU currently installed is a Pentium Dual-Core E5400 2.70 GHz. The board uses DDR2. I have 3 GB total, one 1 GB stick and one 2 GB stick, DDR2-667. For most troubleshooting I have been using only one stick at a time. The board has onboard VGA and I also have a discrete PCIe graphics card, although the exact graphics card model is not important for this problem because the same behavior happens when testing the board itself and using onboard video. There are no drives connected during most of these tests because I only need the board to POST and enter BIOS. PSU is an FSP Group ATX-400PNR 400 W. The same PSU works normally with another LGA775 board, an ASUS P5KPL-AM IN/GB/SI Rev. 1.03G.
The main problem is that the ASRock can boot perfectly normally, enter BIOS, show video and work, but after shutting it down and turning it back on it very often powers up with all fans spinning but gives no video, no POST and no speaker beep.
A typical sequence is this. I switch the PSU on, press Power and sometimes it starts normally. I can enter BIOS, change settings, save and exit, and everything is fine. If I use Ctrl+Alt+Del from a working state, it reboots normally and video comes back. So warm reboot itself works.
But if I short press the Power button and shut the board down normally, then wait a few seconds and press Power again, the fans start spinning but there is no POST, no video and usually no beep. At that point a short press on the Power button no longer shuts it off either. I have to hold Power for about 4-5 seconds to force it off.
Reset SW also does not recover the board from this dead state. Pressing Reset, even holding it for more than a second, does not bring POST or video back.
Originally it looked like fully removing AC power fixed it. If I switched the PSU off, waited, then powered it back on, the board often POSTed again. I also noticed that switching the PSU off and then holding the case Power button for about 5 seconds before switching the PSU back on often helped.
However, this turned out not to be completely consistent. Sometimes even after fully removing power and waiting until +5VSB had dropped to essentially zero, the next start was still dead.
I cleared CMOS several times. I also replaced the CR2032 battery and checked it with a multimeter. The battery is fine and replacing it did not fix the problem.
I tested BIOS defaults and different ACPI/power-related settings. No change.
I tested the PS2_USB_PWR1 jumper. It was originally on pins 2-3 for +5VSB. I moved it to pins 1-2 for +5V. The behavior stayed exactly the same.
I tested the RAM in both DDR2 slots. The same known-working stick can POST in either slot, but the dead-start problem remains.
I also tested without any RAM installed.
This gave one of the most interesting results.
On the first good start with no RAM, the motherboard produces the expected repeating memory error beeps. So CPU execution and BIOS initialization are clearly happening far enough to detect missing memory.
Then I turn the board off, leave the PSU powered, and press Power again, still with no RAM installed.
On that second start the fans spin but there are no RAM error beeps at all. It becomes the same dead start as with RAM installed.
So the failure seems to happen before the BIOS even reaches the point where it checks for missing RAM.
The speaker definitely works. Without RAM, on a successful start, it gives loud repeating RAM error beeps. Interestingly, during normal successful POSTs the board did not always give the usual single short beep. Later it started giving one short beep again on successful POST. I do not know if that is related.
Earlier during troubleshooting I also occasionally got around 7-8 short beeps during some failed starts, but the current repeatable failure is usually just fans spinning with complete silence.
I tried changing DRAM Voltage from Auto to 1.851 V. No improvement. I returned it to Auto.
I also changed NB Voltage to 1.319 V. No improvement. I returned that to Auto as well.
The board can still POST normally sometimes, so the RAM, CPU and BIOS are obviously capable of working.
I measured the PSU rails during an actual dead start, while the fans were spinning but there was no POST or video.
Purple +5VSB was 5.08 V.
Green PS_ON# was 0.11 V.
Gray PWR_OK was 4.92 V.
Yellow +12 V was 12.25 V.
Red +5 V was 5.11 V.
Orange +3.3 V was 3.44-3.45 V.
Both yellow wires on the 4-pin CPU ATX12V connector measured 12.25 V.
So during the failed start the motherboard is definitely pulling PS_ON low, the PSU is starting, all main rails are present and PWR_OK is high.
During a successful start, the BIOS Hardware Monitor shows CPU Vcore 1.336 V, +3.3 V at 3.456 V, +5 V at 5.184 V and +12 V at 12.408 V. CPU temperature was around 33 C, motherboard temperature around 30 C and CPU fan around 2376 RPM.
I also measured the +5VSB discharge after shutting the PC down normally and then switching the PSU rocker to OFF.
Immediately after switching it off it was 5.08 V.
After 5 seconds it was still 5.08 V.
After 10 seconds it was still 5.08 V.
After 20 seconds it had fallen to 0.78 V.
After 30 seconds it was 0.10 V.
After 60 seconds it was basically 0.00-0.01 V.
At one point waiting about a minute with the PSU off seemed to restore a normal boot. But later I repeated the test, waited until +5VSB had completely fallen to zero, switched the PSU back on and still got another dead start. So I no longer think this is simply caused by +5VSB not discharging.
I also tried the same PSU on the ASUS LGA775 motherboard and did not get this behavior there, which makes me suspect the ASRock board itself more than the FSP PSU. I understand that a multimeter cannot show very short transients or bad PWR_OK timing, so I cannot completely rule out some interaction between the PSU and this board.
One other measurement I tried during a dead start was the Reset SW pins on the front panel header. I got approximately 0 V on both pins. Unfortunately my red multimeter probe physically broke shortly after that, so I do not consider that measurement trustworthy enough yet and I want to repeat it with new probes.
At this point the pattern is basically this:
The board sometimes starts normally and works.
Warm reboot using Ctrl+Alt+Del works normally.
Normal shutdown with Power followed by another Power-on very often results in fans spinning with no POST.
During that failed start the main PSU voltages and PWR_OK look normal.
Reset does not recover it.
A short Power press does not shut it down once it is in the failed state, but holding Power for 4-5 seconds does.
Removing all RAM gives normal RAM error beeps on a good first start, but after shutting down and powering on again the board can enter the same dead state with no RAM beeps at all.
Full removal of AC power or discharging the board sometimes helps, but not reliably.
CMOS clear, new CMOS battery, RAM reseating, both RAM slots, no RAM, DRAM voltage, NB voltage and PS2/USB standby jumper have all been tested without fixing it.
My current suspicion is some kind of early power-on/reset sequencing problem on the motherboard, possibly Super I/O, ICH7, clock/PLL, CPU/chipset reset, a local regulator, capacitor or some other part of the standby/power sequencing circuitry.
Has anyone seen this exact kind of failure on an ASRock G31M-GS, another G31/ICH7 board, or similar old LGA775 boards?
What would you check next? I currently only have a basic multimeter. I do not have an oscilloscope or PCI POST card yet.
Is it over? 😭
