[ltp] Fixing a bad inverter board on a 770 TP

M. Leo Cooper linux-thinkpad@linux-thinkpad.org
Sat, 28 Jun 2003 20:10:41 -0700 (MST)


The following applies to a 770 Thinkpad, "Type 9548," with a 13.3"
LCD screen.  I imagine a very similar procedure would work with other
770 models.

First, how do you know it's actually the inverter that has gone bad? An
inverter that is getting flaky usually gives you some warning ahead of
time -- screen flicker, "tearing" of the display, display going dark,
then coming back again, etc. About the only other screen hardware failure
I've ever heard of is the backlight burning out, and that, I think,
goes all at once, and the screen stays dark. A bad inverter acts flaky
for a while before going totally bad.

I got a replacement inverter on eBay. It was $20 (plus $8 shipping). You
have to make sure you have the exact model inverter you need, because
these are *not* interchangeable among different 770 models. The part
number on the front of this particular inverter is "INVC479". This
number is visible on the front of the inverter board. The "P/N" and
"FRU" numbers are 05K3113, and 05K3114, respectively. These are on a
paper label on the back of the board.

The inverter is actually a circuit board, 7" long by 1/2" wide. It has
a plug-in connector on each end, and is held in place by two screws.

The replacement procedure:

Open the lid of the laptop. Remove the three screws at the bottom of the lid,
as the screen is facing you. These screws are concealed by round black paper
"stickums," which you have to peel off before you can get to the screws.

Now you will remove the "bezel." This is a narrow rectangular frame of
black plastic that conceals the edges of the screen within the lid. With
the three holding screws removed, use a narrow screwdriver or blunt knife
blade to lift the bottom of the bezel up slightly. Then pull the bezel
toward you with a *gentle* side-to-side rocking motion. If you are lucky,
you won't break more than one or two of the plastic retaining hooks that
hold the bezel to the lid. (A broken hook or two won't matter.)

With the bezel removed, you can see the inverter board, mounted just below
the screen in the lid. You have already removed the center retaining
screw holding the inverter board when you took off the bezel. You need
to remove one more screw, the one on the left side of the board.

There are two cable connectors to the inverter board, one on each
side. The two-wire connector on the right side removes easily, but put
a mark on it with a pen before disconnecting it so you can keep the
correct polarity when you reconnect it to the new board. To pull out the
connector on the left side, you will have to remove the screw holding
the cable. This screw is located to the left, about 1/2" off the side
of the inverter board.

With the retaining screws removed and the cables disconnected, the bad
inverter board lifts right out. Install the replacement inverter board
with the same orientation as the old one. Put in the screw on the left
side (*not* the center screw yet, this one will go in through the bezel).
Reconnect the cables, carefully observing polarity. Replace the cable
retaining screw on the left.

At this point, you may wish to test the display by plugging in the
power supply. Careful not to touch any of the exposed circuits with the
power on.

With power off, replace the bezel. It slips back on by pressing it
forward and down, toward the top of the lid. The only tricky part here
is lining up the brightness control slide-switch on the inverter board
with the slide-switch on the bezel. Move the slide all the way to the
left on both the inverter board and the bezel before replacing the bezel.

Make sure the screw holes in the bezel line up with the holes in the
lid and inverter board. Some slight jiggling may be necessary. Replace
the three screws.

If you have had the foresight to save the black paper "stickums,"
you can stick them back over the screw holes. (I lost two of these
"stickums." Does anyone know where I can get replacements?)

The repair job is now complete. Total time is maybe 20 minutes.

Note: You will *not* need to remove the lid for this repair. Removing
the lid complicates matters greatly and adds at least an hour to the
repair time.