Stuck Before Boot No Screen Led On Caps And Num Ok Fan Spins Toshiba Satellite C850

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Whether on battery with or without power adapter plugged in, or on AC without battery inserted the same behaviour happens: the laptop does not boot, both LED turn on, num lock turns on (switches on/off when pressed, same for caps lock), short press on power button instant turns off, after a little while the fan starts spinning because the laptop starts heating. screen stays black. it seems stuck at a early stage of boot or pre boot. I tried disassembling it down to the bare motherboard with only the power switch and power plug attached and it shows the same behaviour. I checked the first mosfet and the have 19V in and out with 24V on gate, so things seems normal here. There is an area that do heat but I cannot pinpoint a precise location. Not sure what I can try next. I should mention that when down to the bare motherboard simply plugging the power cord turns it on (LEDs turn on and so on). Any suggestion welcome.

Hi Jo, It looks like that one of the ic’s around the CPU and the gpu is getting too hot. Check which one is heating. Use some of alcohol 99% to figure it out. Enable the circuit after pouring the alcohol And observe it. Another way test for short circuits in the same area using a multimeter in ohm or diode mode. Good luck

Have you tried these standard solutions yet? ·         Soft Power Cycle: 1.       Press and hold down the power button for 20 seconds or until the computer shuts down. 2.       Press the power button to turn the computer back on 3.       If this did not resolve your issue continue with the Hard Power Cycle procedure  ’’ ·         Hard Power Cycle (For computers that have removable batteries): 1.       Unplug the computer from the AC adapter. 2.       Remove the battery from the computer. 3.       Press and hold the power button for 20 seconds. 4.       Re-Install the battery. 5.       Re-Connect the AC adapter. 6.       Press the power button to turn the computer back on   ·         Look for tiny hole the size of paper clip on the underside. This is a reset on some Toshibas. Stick in end of paper clip for a few seconds.   ·         Reset BIOS by shorting contacts marked JCMOS.