Dell Ispiron P102F, motherboard Wistron Mockingbird N AMD 19852-1

[wasteinc]

Hi, I'm new to laptop repairing, but not new to electronics. I just opened a laptop a friend gave me (no power) , and I was hoping for shorted main power rail , a bad capacitor or a bad dc-in mosfet. Up until now I haven't found a short or something obviously burned, the dc-in mosfets seem to work ok, the + on the big capacitors close to the CPU have an OK resistance to ground (around 14-15ohm) but following this thread here I connected the motherboard to the power brick to check the voltages. I didn´t do a lot of poking around when I noticed that the CPU was rather hot (over 55-60C to the touch). I guess this is a bad sign, as I just plugged the dc-jack on the naked motherboard, so It shouldn't try to turn on and get the CPU hot.



Checking again, the power brick starts consuming 7-8Watts of power when plugged into the motherboard after a few seconds. Is it normal for motherboards to turn on like that? I guess no as the control chip should turn off the power if it notices such a short...

My question is is there something obvious I am missing, do motherboards just turn on by themselves like that when you plug them in???

Thanks for your insights and patience

[wasteinc]

PS To continue the story, I just plugged some connections back on the motherboard and it seemed to turn on now. I thought It would be some peripheral component that was shorted so I plugged things one by one and lo and behold everything seems to work fine this time around. For some background this laptop had its motherboard replaced by a "professional" Dell technician who came to my friends home and a few days later died. My friend complained to dell and they sent him a replacement laptop and never asked for the broken back. The dell technician was either very bored or it was his first time as the screws were in a bad shape (just philips screws) and the motherboard had scratches so bad close to the BIOS with a few revealed lines. That was my first concern but after testing and inspecting the scratches I found no broken continuity to the legs of the BIOS chip.

So I don't know maybe it dies again, or the guy didn't properly placed something that was shorting or making the laptop unable to boot. Will let it run a bit to check...
If you still have a similar story please share the issue you had because I kind of have a love-hate relationship to electronics that magically work after I touch them with my fingers

Thanks for reading

and cheers

[mcplslg123]

Newer motherboard's RTC circuit is inside backup battery-so when you remove the backup battery,its expected to turn on its own when adapter is connected due to RTC reset.

Put the heatsink back and measure voltage on all coils.

[wasteinc]

Thanks for that , last time I repaired a laptop mobo was when laptop mobos didn't look like mobile phones , so I got really surprised

Turns out everything seems ok, I will torture the laptop now to see if something gives.....