Question HP Omen 15 - No image after thermal paste replacement

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I have an HP OMEN 15 CE 198 WM. I used it for 5 years and the temperatures started going up after some intense use so I decided to open it to clean the coolers and change the thermal paste. I did so with great care. I used Deep Cool Z5 which highlights its dielectric properties. Also, the embedded CPU and GPU have a sort of plastic cover around them, making spillage more difficult. I assembled everything back the way it was, and there was no image on the screen.

I tried many different things, so in no specific order:

- Removed the battery and pressed the power button for 60 seconds, then turned it on with the AC adapter
- Removed 1 RAM module, switched the slot, then tried the other one and did the same.
- Unplugged the display adapter and plugged it again.
- Connected the HDMI output to a TV screen.
- Removed the thermal paste and applied it again
- Left the laptop without the battery for 3 hours after pressing the power buton 60 seconds

As you can probably imagine, nothing worked. The laptop starts for 6 seconds, then powers off. Then powers on again, and sometimes this cycle is repeated a couple of times, other times its just once. After this, it keeps on and I'm guessing Windows starts because I need to press the power button for several seconds before it turns off, a typical behavior when the OS is working. The HDD led also works as if it were normally booting into Windows. If I press it the first few seconds it's booting, it immediately powers off.

What can this be, and is there any way to solve it? Additionally, I "think" the last thing that the computer did when it was still working was an update, I'm not sure because I wasn't the one using it.

Any further ideas will be appreciated!

 

[Lutfij]

Also, the embedded CPU and GPU have a sort of plastic cover around them, making spillage more difficult.
Did you apply a pea sized amount on the center of the die's or more than that? Got images of how the spread/application of the thermal paste is? What about thermal pads?

Disconnect the laptop from the wall, disconnect the battery, remove the rams and use an eraser to clean the gold contacts on the ram stick(s). Press and hold down the power button for 30secs, then reseat the ram in the slot it was originally in(making sure there are no eraser lint on the gold contacts. Power up using the power brick, not the battery and see if that helps.

 

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Did it. It turned on, immediately turned off. Then turned on again for a couple seconds, then off. Then on again and remained so until I powered it off by pressing the power button for a couple seconds. Still no image on the screen.

Then I switched the RAM modules and it made a sequence of turn on/off a bit different from before. It was like 1 second, then 10, then like a minute and then it stayed on. This time I noticed the HDD led blinking a bit more.

I don't have a picture but I can remove the heatsink again and take one. I used a small dot on both CPU and GPU. Even if I did a poor job at it, I guessed it would start and then immediately go off as the temperature exceeds the safe threshold. I'm pretty sure nothing got disconnected as you don't need to disconnect anything to remove the heatsink and there are just three or four connectors around. Thermal pads look okay, even if one was a bit torn.

I tried inserting an image of the motherboard from my Google Drive with sharing enabled but it doesn't let me. I uploaded it to Imgur, here's the link

https://imgur.com/a/kH4Gx57

View: https://imgur.com/a/kH4Gx57

 

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I used compressed air to blow the fans, maybe some junk was there and is shorting the motherboard somewhere?

 

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It was like this when I removed the heatsink today, and it looks very similar to what I originally saw when I was about to replace the thermal paste

https://imgur.com/a/1qmFX5Q

View: https://imgur.com/a/1qmFX5Q


I turned it on and the same thing, first, it stayed on for a sec, then powered off or reset. Then on for about 10 secs, then off again. Then on and remained on. If it helps, the keyboard backlight is as it was configured via the OMEN software. I removed all thermal paste and this is how it looks like now:

https://imgur.com/a/kLtesu5

View: https://imgur.com/a/kLtesu5