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Released in 2012, the Toshiba Satellite C850 is a 15.6-inch notebook with a choice of either AMD or Intel processors. It has USB 3.0 and can be configured with up to a 1TB HDD for storage and discrete graphics.

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stuck before boot, no screen, led on, caps and num ok, fan spins

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.

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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

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I suspected a shorted IC or a BIOS issue. I'll try to locate where the heat is coming from.

-edit-

I dropped some alcohol in the area that seems to be the source of heat and looked under the microscope. Nothing obvious appeared so I add more alcohol and it seems to have made a connection it was not supposed to, the board powered off and instead of the white and orange LED on I had the white one blinking. Once alcohol has evaporated I'm back to the start.

由完成的

After a few minuthes several components are generating heat, the hottest part seems to be the intel motherboard chipset SLJ8E. I'm unsure this means the short is there, how can I test further ?

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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.

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Tried that, also tried to remove the bios battery and short the pins for a 10 seconds.

I'll look for JCMOS contacts.

-edit-

looked all over the board and found JCMOS or JPW contacts.

a web search points that it should be under the RAM but not on my model.

I did find a JRST2501, JRST2001 and JRST2002 around the BIOS battery but I have no idea what those are for.

only place I have looked is under the cooling system heatpipe.

由完成的

I found some info online:

https://www.justanswer.com/laptop/7u6gl-...

https://www.youtube.com/watch?v=mUZ6_mxT...

https://www.techinferno.com/index.php?/f...

JRST2501 is to reset BIOS password

JRST2001 is to clear CMOS

JRST2002 is related to TPM and clears ME RTC registers

I tried shunting JRST2001 without AC with CMOS battery and with both. did not try without CMOS battery.

it did not help so it seems it was not a BIOS issue.

由完成的

Good information. Will help some people at leats. Unfortunate it did not help you.

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