Laptop won't boot after RAM upgrade

[racquad]

I have a 15s-fq1510na laptop that had 1x4GB original and 1x16GB added later. It was working fine until I bought a new 1x16 GB stick (same DDR4 2666MHz speciification as the other ones).

At first it did not boot, black screen. So I removed the new stick and nothing. After a few combinations the only way the laptop POST is with 1x4 GB. Any other possible combination it simply does not POST.

I've tried to upgrade BIOS to latest. Upgrade was successful but still no practical results on the RAM upgrade.

I don't know what to do since now I will have even less memory than I used to have.

[erico]

The 16 GB memory needs to have the following specifications.

DDR4 2666MT/s Non-ECC Unbuffered SODIMM CL19 2RX8 1.2V 260-pin

Mixing memory modules of differing row and CL timing can often result in the problem you are having.

When the memory training takes place weird things and frustration  can happen

That is why the best practice is to only upgrade with guaranteed compatible memory modules that are identical in all respects.

Online source of guaranteed compatible memory

https://www.kingston.com/en/memory/search/model/101081/hp-hpe-15-series-notebook-15s-fq1xxx-series

[racquad]

I know but strangely enough the computer won't boot with the original 16GB stick anymore which doesn't match with your explanation.

Your explanation fits for the case the new 16GB stick is from a different spec. But what about the original one that's now rejected?

[erico]

You are asking me to  provide an explanation or guess  about something without having any real specifications to use as reference material.

[racquad]

No, I'm asking for help about an awkward behavior.

I understand and appreciate your explanation over the possibility of unmatched specifications on stickies. But it doesn't explain why computer used to work with 1x4 + 1x16 and now it refuses to POST with the same configuration, same stickies, same slots. That's the part I don't understand.

[erico]

It is because you installed incompatible memory modules. 

When the  BIOS memory training process happened at the firmware level it did not complete.

Memory training, in  its essence, is comparison of the memory timings, voltages, etc against the set of timings and voltages that the BIOS ROM coding has stored as being valid.

That is why the best practice is to upgrade with identical guaranteed compatible memory modules. 

I follow that best practice and it has not failed me.

I am certain that the PC was not delivered with 1x4 + 1x16 as its configuration.

I would not have installed a config like that and expected it to work.

You say it worked, but now no more.

That does not surprise me.

[racquad]

Here's what I did and worked out (for anyone else with similar issue).

1. Turned down the computer, unplugged from power cord and detached battery.
2. Left several hours like this to be sure that any capacitor is fully discharged
3. Reassembled memory sticks and battery
4. Turned on
5. POST recognized both stickies and I have the full 32 GB

Of course you need to check for all compatibility mentioned before (as I did) but there was something else to be done. Follow these steps if you have the same POST problem I've had.