This laptop arrived with blinking Power Light (on side). It would not turn on, would not P.O.S.T. and no other signs of life.
Step one: Test the usual obvious problems. this is the order in which I test parts for failure.
a. MOSFETS - testing with meter in DIODE mode, they will have some value one direction, and Infinity in the other direction. Depending on the type N-Channel or P-Channel will show a values. And they are opposites-
N-Channel may show ~475 with Positive on Source, and Infinity on Drain
P-Channel may show ~475 with Negative on Source, and Infinity on Drain (There are other posts detailing which does what somewhere on this blog)
Step two: Test the Diodes
Step three: Test the Resistors
In this particular case, the defect was found testing MOSFETs. Though it was somewhat painstaking, I choose to remove the MOSFETs and test them out of circuit. Why? Simply because you can get erroneous reading from other parts in the same circuit, which will waste more time. It can become a conundrum where a whole section will show as shorted.
|Red and Blue X shows Mosfets I removed|
YELLOW Tested in circuit, did not have to remove.
RED Tested out of circuit, removed and tested on bench.
BLUE The shorted MOSFET, found and has 2 OHMS in both directions - Dead Short (meter may be out of calibration- it was free from Harbor Freight during a special, so...)
Clean the part removing flux so that you can clearly read the numbers and then replace. These parts are in pairs (2 each) xx86 & xx36 it can be confusing if you do not verify the numbers. The easiest way is to take a photo before removing if you don't know which part goes where. [I use a digital microscope for closeups]
|Testing Mosfet with Meter|
and another after the mosfet was replaced. So you can see what/how the power light was blinking/flashing.
The second video shows after repair.
Please do not email questions on how to repair a laptop, I can only show you what I did to find the problem and fix it. Again this site is intended for experienced technicians.