Samsung NP300E5C turns on once, then won't turn on again

[PinGuy]

On cold start laptop works perfectly (no crashes or anything), but if shut down and power back it won't turn on until left resting for a while (maybe 1+ hour, sometimes even more).
When it doesn't work it powers on but the fan starts at full speed and the screen stays black.
I found a similar issue here: https://www.badcaps.net/forum/showthread.php?t=76745
I replaced the NEC Tokin with 4 caps but there was no difference.
I noticed that when it stays black, the CPU would not heat at all, the PCH does heat, and the voltages all seem fine. It looks as if the CPU is the only thing not being powered on.
Any clues on where to look at?
Maybe a bad thermal sensor?

[mcplslg123]

Re: Samsung NP300E5C turns on once, then won't turn on again

Vcore missing can be for many reasons but since it working at times, perhaps there is some corrosion or connectivity issues. Clean the mb with IPA and look carefully under microscope/magnifying glass. If all is well, check voltage on coils when its not booting. Flash a known good clean me bios as first step but remember to take backup of original bios. You can make request for bios in "bios section"

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

Actually it is an NP300E5A, not C (my mistake).
Burnt a new BIOS, this one specifically: https://www.badcaps.net/forum/showthread.php?t=76143 (thank you, @peste!)
Laptop turned on, I went to BIOS Setup to enable UEFI to boot, then booted fine to Windows. Restarted 3 or 4 times (without powering off) and no issues. Then I turned it off and without moving anything, turned it back on: black screen, fan at full speed. And now it won't power up again until I leave it there for a few hours. Tried shooting freezing spray at various places but no luck. This is a tough one!!!

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

Left the mobo 30 minutes in the freezer, and it doesn't power on

[PinGuy]

Re: Samsung NP300E5A turns on once, then won't turn on again

OK left it resting there and now I turned it on again. Started right away! Went to the setup, wiggled the memory, pressed and gave some hits to the mobo at various points, no crash. Turn off. Turn on again: no picture. This is f'n insane

[SMDFlea]

Re: Samsung NP300E5C turns on once, then won't turn on again

Left the mobo 30 minutes in the freezer, and it doesn't power on

Post your original bios in the bios requests section.

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

@SMDFlea I used the BIOS @peste posted, after cleaning it with me_cleaner, do you think this issue can be ME related? I just turned it on and it started, I measured all voltages OK. When it doesn't boot, Vcore stays at 0 and it is the only missing voltage.

[mcplslg123]

Re: Samsung NP300E5C turns on once, then won't turn on again

When Vcore goes missing, VCCSA & 1.8V present??

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

This mobo doesn't have a silkscreen, and I don't have the boardview for it. I do have the schematic (attached). Which one would be VCCSA?
Attaching pics of the mobo as well.

[SMDFlea]

Re: Samsung NP300E5C turns on once, then won't turn on again

@SMDFlea I used the BIOS @peste posted, after cleaning it with me_cleaner, do you think this issue can be ME related? I just turned it on and it started, I measured all voltages OK. When it doesn't boot, Vcore stays at 0 and it is the only missing voltage.

me_cleaner isn`t very good,cleaning the ME should be done with flash image tool for proper results.Your bios and micom version are very old.Post your original bios backup in the bios requests section.

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

Ok just uploaded it. A doubt, when you say "cleaning the ME" you mean removing most parts of the ME like with me_cleaner? I thought it was good for that, and that the flash image tool was just for restoring it to original condition, not removing/disabling the "big chunks" of it. TIA

[SMDFlea]

Re: Samsung NP300E5C turns on once, then won't turn on again

Ok just uploaded it. A doubt, when you say "cleaning the ME" you mean removing most parts of the ME like with me_cleaner? I thought it was good for that, and that the flash image tool was just for restoring it to original condition, not removing/disabling the "big chunks" of it. TIA

I didn`t mean that tool,i thought you meant some other software that does a similar thing as Intel flash image tool. me_cleaner that strips out parts of the ME firmware isn`t really recommended though for laptops.I`d only use it if its known to work ok on a particular model and its tried and tested with no reported problems.Its ok on some older desktop PC`s

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

Ok, I burnt the BIOS (thanks for it!) and upon restart, didn't start again and vcore went to 0, so it was not a BIOS issue
The sequence now is: it powers on, but the power LED remains off, about 10 secs later the power LED goes on, and the fan starts full speed. I guess as the vcore stays at 0, it is not making the post-update init. I will leave it resting there for some hours and check again.

[mcplslg123]

Re: Samsung NP300E5C turns on once, then won't turn on again

There are two small coils near ram slot. perhaps they are for 1.8V/VCCSA. Not sure but you can measure on these two coils when mb is working/not working to find out the rail which goes missing besides vcore.

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

After leaving it alone overnight it did not power on, not sure if it is the new bios, or that the failure went permanent... Will keep looking and maybe I go back to orig bios to confirm. If it starts at some point, I will check all coils to try spot the differences.

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

Ok, reflashed orig bios just in case and it is in the same condition. I measured all the coils and get 5.1, 3.3, 1.08. The 3 big ones near the processor measure 0V, and the big resistors near the RAM sockets one is at 1.8 and the other one at 0.9. The one on the other side is the 1.5V, also present. So as it seems, the only thing not being powered on is the CPU, maybe some sort of protection is tripping? Will leave it there more time to check again if it powers up again

[mcplslg123]

Re: Samsung NP300E5C turns on once, then won't turn on again

VR_ON is present on ISL95831?

[PinGuy]

Re: Samsung NP300E5C turns on once, then won't turn on again

I just checked again after a rest of more than 12 hours and it didn't start. VR_ON goes from 0 to 3.04V after the 10 second delay for bios init (which didn't finish yet as it didn't power on properly), and 2 seconds before the fan would start at full speed.