My laptop CPU Fan runs normally, but it is blank screen..
Q：After pressing the Boot button, CPU Fan runs normally and indicator light is on, however, it is blank screen, even external monitor (Model IBMX31) died, what’s up?
A: Failure Analysis: CPU fan’s working indicates that system power supply unit works perfectly, while CPU unit circuit is OK too.
Examining and repairing: the chip MAX1845, which supplies power for North Bridge, was tested that it didn’t work. There are about three possibilities why the unit failed:
1. Working conditions are not achieved (such as power supply, control)
2. Power chip MAX1845 fails to work
3. Short circuit inside north bridge which causing MAX1845 not to work.
And my test results: MAX1845 chip is clear for 16V main power supply, stitch 11and 12 high level are both OK.
But the two low-side tubes outside, their control electrode are still protective 5V. The failure is eliminated after changing the Q45 and Q46.