Laptop Model: Lenovo N40-70
Motherboard Number: LA-B091P REV:1.0
Fault : The Laptop Is Not Powered On And The Common
Point Is Short-Circuited.
Repair Process:
If the common point is
short-circuited, the machine will burn out according to the previous routine.
As a result, the filter capacitor at the common point is not short-circuited.
It seems that the fault of this board has been underestimated. I
thought that it would be OK to pry off the filter capacitor. It is not that
simple. .
Finally, it was determined that PU401 was
short-circuited. Look at the drawing + 3VALWP power supply standby chip.
Remove the PU401 common point and it is no longer short-circuited.
Remove the parts on the material board and replace PU401.
Measure the common point again and there is no short-circuit.
PU401 becomes hot when powered on directly.
Looking at the drawing, this chip not only outputs +3VALWP voltage, but also outputs +3VLP linear voltage. Measuring the resistance at both ends of PC412 is directly 0, the linear voltage of +3VLP has many places to go!
In order to save time, I
guessed the EC directly. After removing the EC +3VLP, the resistance value is
normal. It seems that I was deceived! Then measure the resistance of PL404
to ground to be 15, and +5VLWP is also short-circuited.
Find where +5VLWP goes, and finally reach U10.
After removing it, the resistance is normal. Cable bridge CPU is not dry
burned.
The EC model is NPCE288N. This EC does not have an external BIOS
chip, but has a built-in program
Brush up the program of this EC
on the forum, solder the EC and U10, press the switch key and the current will
turn on normally like a wild horse!
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