Trying to troubleshoot DDR4 SODIMM slot with slot tester

[Lifeisfun]

Hi folks!
I have some kind of memory problem on Lenovo laptop. I was initially able to install windows after several tries since the laptop did freeze in middle of those attempts.
Eventually I discovered that it was related to moving the laptop.
Later on it even stopped booting unless I pressed around the memory slot. (no keyboard LEDs only power button responds)
If I remove the RAM I get the beeps that RAM is missing. Inserting the RAM there is silence and it will not boot most of the time. No picture.

I removed the board got one of those memory slot testers and I'm not sure how to proceed.
Some LEDs are brighter than others but there is couple of the not lit.
DM0
DM1
DQ6
DQ10
ALERT-N
CS1
OD1

I'm not sure how this tester works since when I randomly checked the connection from the corresponding LED it did connect all the way to the memory slot soldering pad.
Also tested those LEDs that are not lit and they are OK.

When I press on the tester it is wonky and lights are not consistent.

I also stripped the board and baked it @ 375F for 8 minutes (applied soldering paste on all pins to refresh the soldering)
No change.

Can anyone please advice how to proceed with fault like this?

Thanks

[Sephir0th]

It is not said that the module itself is faulty. Test it in a known working system before to exclude the worst case: Cracked solder balls underneath the CPU.

Baking the board was not only pointless but also a really bad move for the PCB health. Not hot enough to melt leaded solder, but definitely hot enough to possibly degrade the CPU.

[Lifeisfun]

It is not said that the module itself is faulty. Test it in a known working system before to exclude the worst case: Cracked solder balls underneath the CPU.

Thanks for reply!
The test module it self there isn't much to it, no active components on it and I did test the traces going to those LED's
Memory it self was tested and works fine.
What I find strange is how the LED blink moving the test module when it's locked in the memory slot
I also applied soldering paste around the CPU while it was baking.
What do you think about the time of the baking and temperature?
From experience how often do you se bad memory socket?


Thanks for your time! You are great!

[Sephir0th]

Rarely and also it can usually be easily checked with tweezer and microscope what you should do next of course. And just in case it is still not clear: you should not bake the pcb again. Things like that should be only seen as the ultima ratio, when you ran out of options, but never earlier since it can leave the board irreparably damaged.

If the socket turns out being good, then the next logical step is a proper reball of the CPU with suitable tools and a oven is not a suitable tool.

[m1ch43lzm]

When I press on the tester it is wonky and lights are not consistent.
....
What I find strange is how the LED blink moving the test module when it's locked in the memory slot

It could be bad solder joints on the RAM slot

375 F (190 C) not enough to melt lead free solder as Sephir0th said, at most you melted the flux you added

Check the RAM slot under the microscope, then poke the pins on the ram slot with tweezers, if they move, touch them with the soldering iron (flux + fresh solder)
Video i found, for reference
https://www.youtube.com/watch?v=4zZmVIwacLg
Skip to 5:50, you'll see what i mean

Or as Sephir0th said worst case, cracked solder balls under the CPU, in that case best to take it to someone with BGA rework machine to reball the CPU
You may have noticed some sort of black glue on the corners of the CPU, many people say that it's difficult to remove cleanly, even damaging pads under it, Lenovo likes to use that black glue/epoxy unlike other manufacturers that use red or clear glue on the corners that is easier to remove

[Lifeisfun]

Rarely and also it can usually be easily checked with tweezer and microscope what you should do next of course. And just in case it is still not clear: you should not bake the pcb again. Things like that should be only seen as the ultima ratio, when you ran out of options, but never earlier since it can leave the board irreparably damaged.

If the socket turns out being good, then the next logical step is a proper reball of the CPU with suitable tools and a oven is not a suitable tool.

Well, I did check it and don't see any problems with the socket but it is virtually impossible to see the underside contacts in the socket.
I ordered new slot and will replace it just for the fun of it I think the most difficult thing will be the old socket removal since one the left and right side (about 10 pins each side)
there is blob of some kind of glue, probably epoxy.
Reball of the CPU is probably not worth it.

[Lifeisfun]

It could be bad solder joints on the RAM slot

375 F (190 C) not enough to melt lead free solder as Sephir0th said, at most you melted the flux you added

Check the RAM slot under the microscope, then poke the pins on the ram slot with tweezers, if they move, touch them with the soldering iron (flux + fresh solder)
Video i found, for reference
https://www.youtube.com/watch?v=4zZmVIwacLg
Skip to 5:50, you'll see what i mean

Or as Sephir0th said worst case, cracked solder balls under the CPU, in that case best to take it to someone with BGA rework machine to reball the CPU
You may have noticed some sort of black glue on the corners of the CPU, many people say that it's difficult to remove cleanly, even damaging pads under it, Lenovo likes to use that black glue/epoxy unlike other manufacturers that use red or clear glue on the corners that is easier to remove

Thanks for your reply as well!
I just posted pics when you posted, yes, that epoxy is seen on the memory socket as well.
I pick the temperature from ideas while goggling on the subject.
Check all the pins and didn't find any cracked.

[mcplslg123]

Replacing the Ram Slot wont solve it for sure as long as there is no loose pins.

Till date, i've not across any lenovo's with ram slot pin issue.however, this is very common fault on newer HP motherboards.

Going by the LED indication of ram slot tester, its cracked ball under CPU 'coz of low melting solder used by lenovo(very common issue with Lenovo's)

So reballing/replacing the SOC is perhaps the only option to fix it and that require a great deal of skill besides tools.

Btw, what's the mb code?

[Lifeisfun]

Replacing the Ram Slot wont solve it for sure as long as there is no loose pins.

Till date, i've not across any lenovo's with ram slot pin issue.however, this is very common fault on newer HP motherboards.

Going by the LED indication of ram slot tester, its cracked ball under CPU 'coz of low melting solder used by lenovo(very common issue with Lenovo's)

So reballing/replacing the SOC is perhaps the only option to fix it and that require a great deal of skill besides tools.

Btw, what's the mb code?

Thanks for reply!
The only thing I'm still thinking here is something wrong with the slot is because the LED are going on and off while massaging the slot while the tester is locked in it.
I tried press on the CPU it self and there is no change how the testing board is lit.
You said Lenovo used low melt solder, does this mean that the 370F temperature I used to bake it was sufficient to reflow the board?
Board is NM-C421
This is just a project, nothing crucial so I'm willing to try anything for good experiment

[Lifeisfun]

Any suggestions what else to try?
Any suggestion can be tested in the name of good experiment
This is what is it all about , to learn something