This unit arrived working from a
charged battery, but will not power on from AC.
My
first thought was bad leg on the DC Jack, Easy job! Finally
Upon opening the case and removing the
keyboard I saw the beginning of the failure. Burnt MOSFET under the keyboard
directly behind the battery connector.
So took the rest of the panels off to see
how bad it was. Out of a scale of 1-10 with 10 being the most difficult I rate
this as a 7.5 because it was more annoying than difficult. The copper under the
MOSFET was actually welded to the legs of the FET, heating solder would not
break the weld.
The
visual shows almost the worse case scenario for a shorted MOSFET. Burnt and
totally unreadable numbers. Seeing the circuit I surmised that it was an
identical pair of chips but I had to verify against another motherboard to be
sure. Also there was a scorch mark under the keyboard, but it didn't
affect the keyboard or any keys.
Removing
part and making a copper bridge for the legs of the replacement MOSFET was
a little challenge getting it right and isolating it
from
the center plane of the motherboard if copper was exposed. In this case a
small piece of Mylar tape will be placed under the copper retrofit.
Sizing
and fitting the copper 'jig'. This was made from thin copper foil and cut with
exacto knife and placement test made to see if the Gate lines were shorting or
any other pads before making it permanent and not being able to remove
it.
Replacing
the MOSFETs and soldering broken traces. In this case the GATE line was
blown away on both FETs so I got 2 small segments of wire and made the
necessary bridges to the GATEs.
Soldering the Gate line and cleaning up.
Now if you wanted to be fancy you can cover the solder and copper with
some green fingernail polish, or clear polish and use a green marker over the
polish after it dries. Then the repair will appear less noticeable.
Notice the line at marking PR152 which was not
so clear as being broken because it goes under the chip.
