Question Very slow POST screen when DIMM slots A1 and A2 are populated

[otringal]

Hi, all!

Recently, my PSU stopped working, so I went out and bought a new one. After installing the new PSU, the PC is turning on, but the POST screen is only showing up after like 40-50 seconds of Black screen.

So, after a lot of fiddling around, I discovered that this only happens if DIMM slots A1/A2 (either one of them or both) are populated. If I use slots B1/B2 (either one of them or both), the POST comes up in like 5 seconds, just like it used to be, so 10 times faster compared to the new behavior.

Yes, I already did many CMOS resets, both with the jumper and with the battery itself, and no, it is not a problem of the RAM sticks either, I've swapped them and I also tried others, as I have a lot of them, but the results are the same no matter what RAM stick or capacity, frequency or latency I use (plus, these RAM sticks worked perfectly before the PSU incident).

I have also used a PCI debug card, to see if there are any relevant error codes when populating the A1/A2 DIMMs, but I get the exact same sequence as in the B1/B2 scenario, the only difference being some huge delays during these phases:

• d5 (Passing control to the uncompressed code in shadow RAM at E000:0000h. The initialization code is copied to segment 0 and control will be transferred to segment 0)
• d6 (Control is in segment 0, Next, checking if <Ctrl> <Home> was pressed and verifying the system BIOS checksum. If either <Ctrl> <Home> was pressed or the system BIOS checksum is bad, next will go to checkpoint code E0h. Otherwise, going to checkpoint code D7h)
• 0c (Detect type of keyboard controller and set NUM LOCK status)

And here are the relevant system specs:

• Old PSU: RPC 45000AB @450W, bought brand new in 2017, lasted for 7-8 years before it stopped working
• New PSU: RPC 50020LA @500W, bought brand new today
• Motherboard: ASUS P5Q-VM-DO
• CPU: Intel Core 2 Quad Q9400 @2.66 GHz
• RAM: 4x 2GB DDR2 Hynix (irrelevant, as the problem is the same with other brands, capacities etc.)
• GPU: nVidia GeForce 750 Ti (irrelevant, as the problem is the same with the integrated Intel HD Graphics)
• HDD, OS and drivers are irrelevant, as my problem relates to the huge delay of the POST screen, everything is fine once the Windows booting sequence starts. Also, the problem is the same with the HDD completely disconnected.

Therefore, I'm not sure if the motherboard got partially affected when the old PSU stopped working, or if the new PSU somehow has less power on one of the supply lines.
So, here are my 2 questions in order to even dare and support any of my 2 theories:

1. is it possible for DIMM slots A1 and A2 to get only partially broken, enough to delay the POST up to almost 1 minute, but once it reaches that stage, to run perfectly fine? Because that's what is happening at the moment.
2. are banks DIMM slots A1 and A2 powered by a different PSU line compared to banks B1 and B2, is this even possible? Or are all 4 DIMM slots powered by the same line? Because I don't have another PSU at the moment to rule out a possible issue with this new PSU I bought.
3. any other ideas apart from my above-mentioned hypothesis?

Thank you so much!

 

[Ralston18]

Update your post to include full system hardware specs and OS information.

Include PSUs: make, model, wattage, age, condition (original/new).

Disk drive(s): make, model, capacity, how full?

Be sure to check the motherboard's User Guide/Manual.

Some motherboards require that the first physically installed RAM be placed in a specific slot. Normally DIMM_A2.

Also verify that you are doing the resets per the User Guide/Manual's procedure.

 

[otringal]

Thank you, I've done that now!

Btw, the HDD, OS and drivers are irrelevant -> my problem happens much earlier, as it delays the BIOS POST screen, not the OS boot screen. Also, completely removing the HDD gives no improvement on the issue. Same goes when disconnecting all the USB & HD Audio front panel jacks or case fans from the motherboard, the problem remains the same.

Every CMOS reset was done precisely as per the User Manual, and as far as I can tell, there seems to be no issue with RAM training, it's just those 2 DIMMs (A1 and A2) which all of a sudden are very very very slow compared to the other ones (B1 and B2).

Moreover, all 4x of my DIMMs are populated by identical (kit) modules, so the order doesn't matter. And when testing with only 1x or 2x DIMMs, the manual actually wants A1 and A2 to be populated first, which in my case are the problematic ones. If I populate B1 and B2 there are no problems, just a POST message saying I should use A1 and A2 (ironically). But anyway, this is just for testing purposes, as I said, normally I'm having all 4x populated.

And I repeat: the reason why I find my problem very weird is because it's not a simple case of 2 out of 4 DIMMs not working. No, they are all working, just that 2 of them are much much slower in getting to the POST screen than the other 2, and it wasn't until the old PSU broke and now having this new PSU.

So, if you've read all my messages, the RAM sticks are clearly not problematic, but I also can't blame the motherboard, nor the PSU, as normally if a DIMM is broken, it simply won't recognize/power on the RAM stick anymore, and if a PSU fails to supply power to the RAM, it should affect all DIMMs equally. Right?!

I'm not sure how the IMC (Integrated Memory Controller) could simply be delaying POST on Bank A all of a sudden, but be completely fine on Bank B...