Asus Strix Z270i Gaming dead DIMM troubleshoot

[Novgorod]

Hi!

I have an Asus Z270i mini-ITX board with a dead DIMM slot (the one further from the CPU). The board POSTs with only the other DIMM populated but gets stuck with the DRAM error LED when the bad slot is populated. The test RAM and CPU are known working (confirmed in a different board, both memory channels are fine). The board was working for many years in a watercooled system and had a tiny bit of corrosion in different places (which came off without issues) and no visible component or trace damage.

What are the steps for DIMM (DDR4) socket troubleshooting? Since the RAM controller is on the CPU (and good), it must be either a connection or voltage problem, I'd think. Which voltages should I look for and does anyone have a DDR4 DIMM pinout diagram? A schematic for the board would be even better but I assume it's too exotic for anyone to have heard of it...

[DynaxSC]

It won't be the voltages, they are same for both DIMM slots (connected in parallel). Check first the cpu socket for bent or dirty pins, then also the DIMM socket itself. You can try to clean the cpu and DIMM sockets with isopropyl alcohol (must be 99.9% clean) and some soft brush. For the cpu socket do it very carefully, slide the brush in direction of the pins, never against. After brushing best is to dry the sockets with compressed air. Look with a magnifier glass for any foreign objects in the sockets. Clean also the cpu pads and the memory pads. If this does not help, then probably the connections of the cpu socket pins to the board pads are faulty. Could it be that somebody before tried to exchange the socket? You can also buy a memory test card on Aliexpress to check which pins do not connect.
Look also very carefully for demaged tracks, especially around the cooler mounting holes. Poor quality cooler mountings can scratch the board and cut tracks. Use a x15 magnifier glass.
Last resort is using a fiber glass pen to clean the memory pads and the CPU pins, but this is really last option, as it can reduce the gold plating of the cpu pins. For memories it is more safe as they have usually only copper pads.

[Novgorod]

It won't be the voltages, they are same for both DIMM slots (connected in parallel). Check first the cpu socket for bent or dirty pins, then also the DIMM socket itself. You can try to clean the cpu and DIMM sockets with isopropyl alcohol (must be 99.9% clean) and some soft brush. For the cpu socket do it very carefully, slide the brush in direction of the pins, never against. After brushing best is to dry the sockets with compressed air. Look with a magnifier glass for any foreign objects in the sockets. Clean also the cpu pads and the memory pads. If this does not help, then probably the connections of the cpu socket pins to the board pads are faulty. Could it be that somebody before tried to exchange the socket? You can also buy a memory test card on Aliexpress to check which pins do not connect.
Look also very carefully for demaged tracks, especially around the cooler mounting holes. Poor quality cooler mountings can scratch the board and cut tracks. Use a x15 magnifier glass.
Last resort is using a fiber glass pen to clean the memory pads and the CPU pins, but this is really last option, as it can reduce the gold plating of the cpu pins. For memories it is more safe as they have usually only copper pads.

I found a DDR4 datasheet and checked all voltages (most are parallel but not all) and they're all good. There was a tiny bit of corrosion in various places (as mentioned before) which I've cleaned. The CPU hasn't been removed until the RAM problem and the socket pins look completely pristine, no corrosion, no bends, no foreign ojects. I checked everything for physical damage but nothing stands out. The actual RAM sticks and CPU are good (tested in another mainboard). I think the only chance to find it is a RAM tester board, but at this point I found a cheap Asus Z170i as a perfect replacement and I don't have another 6/7th-gen CPU to continue down the rabbit hole, so I'll probably just sell it as "working with 1 RAM stick"...