DIMM slots 1 & 2 not passing integrity check after reseating GPU / CPU with thermal paste

[nfable]

I've had to address overheating issues on my late 2014 4k iMac by getting in there and doing a thourough cleaning and also replacing the original thermal paste.

Upon reassembly the Mac would not boot. I researched online and found some people speaking about reseating the RAM on a black screen, no power up situation. I did this, then got 3 beeps then silence, 3 more beeps.

This points to RAM not passing integrity check, either bad ram, poorly seated, or ¯\_(ツ)_/¯ .

So using a trial and error (I had 3 diff brands of applicable ram) I've determined all the chips are fine and wil work in slots 3 or 4 or both 3/4. However, when any RAM is in DIMM slot 1 or 2, the three beeps start again. This was not this case prior to entering the Mac to clean.

The RAM remained in the little caddy thing while I did all the cleaning, I didn't remove them which would've exposed the slots to debris so I don't believe that's the case.

I've seen on some recommendations to check the tension of the mounting torx screws on the logic board, but not sure how that would affect just 2 dimms. Right now, I'm working with just slot 3&4 and system seems fine, reset PRAM which made the startup chime louder by quite a bit. I'm wondering if I just play it cool and use the Mac for some hours, then try to add more RAM if that'll do it.

Really at a loss here... even thinking would 32GB in form of 2x16gb in slot 3+4 work but I ain't holding my breath.

So, what should I do folks? Any advice appreciated.

 

[nambuccaheadsau]

Mactracker advises maximum is 32GB over four slots may mean it can't handle the 16GB modules.

 

[nfable]

Mactracker advises maximum is 32GB over four slots may mean it can't handle the 16GB modules.

I figured as much, thanks 'nam for confirming.

 

[Tom.Tom]

Hi,

Have you ever resolved this issue, I have recently come across the same issue in 2011 iMac?

Edit: OK, I have just solved mine after some googling - have done NVRAM reset twice in a row and SMC reset twice and slots 1,2 started to work.

 

[nfable]

Yes, mine was totally my fault. In re-pasting the CPU & GPU, upon securing the heatsink with screws you have to turn the HS + board over in your hand, it's really a clumsy unfriendly process - I wish there was a clamp that would secure the heatsink in place while you did a final tighten with screws.

Anyhow, in turning the components over to access the screws, the heatsink slipped ever so slightly which allowed the CPU to slide out of socket and I began to tighten the heatsink on a misaligned CPU. I saw my error, but not after some initial tightening. I reset positions, then tightened and reassembled, that's when my beeps started.

After another teardown, I saw the CPU was actually bent to a small degree and some pins on the board were crushed / pushed out of alignment. I left the cpu alone and corrected the pins very very very carefully until the direction / height looked correct. Repaste and reassemble, then it worked with all slots. So issue was bent cpu pins not making contact with the points on the CPU that I suppose are responsible for talking to those dimms. Curiously, the computer ran ok despite the bent pins.

Glad your issue seemed less scary.