I have Toshiba C850 6050A2541801-MB-A02 with PCH (HM76) damaged laptop and I replaced the PCH with another. After I replaced it, when I pressed power button it turn on and off. after few seconds it again turn on automatically and continue to boot. or if I pressed power button immediately it went off in the first time, it continue to boot.
After booting to windows I checked all the ports and part are working without a problem. Where would be the wrong for this strange problem.
I have same thing on another laptop which is Toshiba C50-A. I replaced the damaged PCH (HM76) with another removed from HP G6.
Posted after 7 minutes 26 seconds:
Another symptom of this problem is it takes 2 minutes to enter BIOS if I pressed F2 key.

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Posted after 8 minutes:
If I pressed and hold F12 and pressed power button laptop will power on 1st time and shows Boot Devices Menu and continue to boot whatever device I choose. Without press and hold F2 (BIOS) or F12 (Boot Devices) It won't power on for the 1 st time. need to press power button again.

Is it related to BIOS?
I have changed many version (dumps from working laptops) but nothing changed.

i have a same problem with c50-a and ithink we need bios dump with clear ME region, but i can't find it
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you need bios dump with clear ME region
place here your bios dump i can try fix it

I returned the laptop to the customer and if i get another C50-A I will upload the BIOS dump for you. Thanks