Lenovo Yoga 2 Pro - stuck in reboot loop before POST

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taynton

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Jun 23, 2016
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Having a terrible time with a Lenovo Yoga 2 Pro (i7, 256GB SSD, dual boot Windows 8.1 and Ubuntu 16). I get power and keyboard lights, but no POST and no change to the screen. After a few seconds the keyboard lights turn off. A few later the power light does. Then its off for a few, then it goes through this again.

Looking like a motherboard problem to me, have tried the checklist here http://www.tomshardware.co.uk/faq/id-1893016/post-system-boot-video-output-troubleshooting-checklist.html without much success.

First symptoms - screen freeze and unresponsive with dashed horizontal black lines. Restarting system would allow the system to boot, but gradually this freeze became more frequent and happening earlier after start-up. Windows seemed to freeze more easily than Ubuntu, but both would freeze with similar symptoms. The system seems to be running hotter than it used to and fans come on more frequently.

I re-installed Windows and the problem seemed to go away for a few weeks. Its returned and is worse. I'd been having trouble with video card drivers, the replase happened not long after I had updated and changed some drivers. I tried to restore to before I updated the drivers, but the system crashed about 10% into the restore.

Now, I'm stuck in a pre-POST reboot cycle. If I plug in the power cord, the system tries to boot, which it didn't before. Pushing the power button or the NOVO BIOS menu button causes the same - system tries to boot but gets in a restart loop. Things I've tried:

30s hold of power button to reset
Remove CMOS battery
Booting with only battery or only mains power (with/ without CMOS battery)
Booting motherboard without connections to other boards/ hardware
Letting battery run down while in loop cycle, then retry
Checked for and cleaned away dust
Took heatsink off CPU/GPU. Thermal paste looked not great if I'm honest but don't really know what I'm looking for.
Tried booting with harddrive disconnected - some have seen a `no hard drive' error that

I *have* gotten it to POST if I leave it off for >24hrs before trying. I was able to get to the BIOS menu for a few minutes before it froze and crashed again. In doing this, I turned off quick boot, thinking that might have been the problem. I also got a BSOD trying to boot to Windows.

All in all I'm pretty stumped. That I can get it to POST if I leave it for hours suggest to me that something is still alive, and that what ever failing has a very slow recovery time. If I had any guess, I would say its related to overheating and shut down of the integrated graphics chip, but I don't know how to test or fix that.

Could it be a polyfuse? Any suggestions on debugging or replacing? Will they get any better if I wait a longer time (say 3-4 days)?

Could it be poor solder connections - I'm thinking of trying an oven reflow, but this would seem to be the opposite of what to do if it is a polyfuse problem?

Any other thoughts of things to test or try?

Thanks for help!
 

taynton

Commendable
Jun 23, 2016
2
0
1,510
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I tried replacing the thermal compound. Didn't seem to help much - I managed to boot and get to the BIOS settings page before it froze and went to reboot loop mode. It had been sitting for about 36hrs, lasted maybe 30 seconds after booting before freezing.

Noticed what looks like some heating damage to the plastic chassis in the CPU area. I found this hack of someone putting a shim to try and press the heat sink more into the CPU board, does that sound reasonable?

I'm also suspect of the CMOS battery - but that the system should be able to boot without it?

Any help or thoughts at all would be great! Petty despirate at this point, trying to squeeze a couple more months out of this machine before I can afford a replacement.
 
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