Dead RAM slots on Intel S5500bc

I’ve used the great information on here to upgrade a linux box with a Intel S5500BC motherboard and a pair of Xeons E5640s.

Everything was working fine after a lot of firmware updates, and a hunt around for the BMC files to sort out the fans running at full speed.

It had 4 x 4GB and 4 x 1GB DIMMS. I swapped out the 1GB ones for 4GB ones to upgrade to the maximum of 32GB (as well as a NAS, this runs Mythtv and Motion (CCTV).

It booted up fine, and BIOS showed the right amount of RAM. However, once booted into Linux, the kernel was only recognising 20GB. Sure enough two motherboard slots had red LEDS lit.

I reseated these. One was still lit, but the kernel recognised all 32GB of RAM.

I reseated the DIMM with the lit LED. However, now on booting I was getting 3 BIOS beeps (fatal memory error). It still booted but the kernel only saw 24GB of RAM (6 x 4GB).

I powered down and swapped a few DIMMS around. End result is that all the DIMMS are fine, except these two slots just always give an error.

I guess I’ve broken something or what?

Any tips?

Thank you.

Have you tested the motherboard outside of the case/chassis?