- Completely Dead.
Instead of ordering a new mainboard, I felt like a challenge so I started troubleshooting. The first thing I noticed was that every time the AC adapter was plugged in, the LED would go out straight away. This cheered me up, as it indicated a short on mainboard somewhere, and this type of problem is fairly simple to repair.
I removed the mainboard & connected it to the bench power supply. Yep, definitely a short as the power supply LCD registered maximum amps. Voltage drops down, amps go up.
It took me 5 minutes to find the short. It was on the underside of the board and it could be located through visual inspection. The area is marked in red.
Here is a closeup, you can see the damage to capacitor PC123
The capacitor is 10uF & is part of a power circuit called a VRM - Voltage Regulator Module. Its a multiphase DC-DC buck converter which steps down the main line voltage (19.5V) down to a level required by other circuits. This one I think is for the CPU (1.075V).
I stripped a 10uF capacitor off a scrap board.
I removed the remnants of the old capacitor & plugged in the bench power supply. Current draw was now perfectly normal. I soldered the new capacitor in.
And fired it up.
Problem solved!!!