HP48GX-repair: keyboard-to-PCB interconnect, how to repair?

[peter dingemans]

G'day everyone,

A while ago my 48GX died; it wouldn't turn on, unless I pressed quite
hard on the keyboard overlay, above the B/C-keys on the top row.

I've opened it up now (destroyed a SMD-resistor, which I've repaired);
between the keyboard and the PCB, I can see an interconnect between
these two. My guess is that there's a bad contact between these (loose
solder, or too low pressure on the contacts).

Now, my problem is: how to get to this interconnect. I can't figure
out how to further disassemble the HP48 without doing lots of damage
to either the keyboard OR the LCD. The metal frame under the keyboard
and the LCD-frame seem to be of one piece; is this correct? If so, I'm
really at a loss on how to disassemble. I've found plenty of
descriptions on the net on how to open up a HP48, but none that have
disassembled it much further....

So, does anyone know how to make this interconnection 'open' for
repair? Or, has anyone had a similar problem and what did you do?

Hope anyone can help,

Grtz,

Peter Dingemans,
The Netherlands.

[Veli-Pekka Nousiainen]

"peter dingemans" <peter_d...@hotmail.com> wrote in message
news:195e9be4.04063...@posting.google.com...

> G'day everyone,
>
> A while ago my 48GX died; it wouldn't turn on, unless I pressed quite
> hard on the keyboard overlay, above the B/C-keys on the top row.
>
> I've opened it up now (destroyed a SMD-resistor, which I've repaired);
> between the keyboard and the PCB, I can see an interconnect between
> these two. My guess is that there's a bad contact between these (loose
> solder, or too low pressure on the contacts).

Too low pressure => the foam is dead, replace with, say paper?
[VPN]

[Maurizio Faccio]

> Now, my problem is: how to get to this interconnect. I can't figure
> out how to further disassemble the HP48 without doing lots of damage
> to either the keyboard OR the LCD. The metal frame under the keyboard
> and the LCD-frame seem to be of one piece; is this correct? If so, I'm
> really at a loss on how to disassemble. I've found plenty of
> descriptions on the net on how to open up a HP48, but none that have
> disassembled it much further....
>

If you can ensure the pressure putting something (a piece of rubber
between the PCB and the plastic case, that press the PCB over the LCD
for example), that is the approach.

Further disassemble the 48, may cause damages that cannot be repaired.
And you cannot warranty the procedure will gave you success. This is
my experience in disassembly the 48, and the level that i have
arrived. I guess that you don't need walk over all the steps (and you
don't want to do it because in each step you walk, the damage will be
worst).

The next step is turn the metal pieces that keep the PCB in its place.
That metal pieces are delicate and may damage when turn it. The
pressure that they ensure is reduced in each disassembly. So you can
start having troubles with LCD display (loose lines, etc)

Next step. The LCD is glued to the metal frame. If you remove, you may
insert it in the wrong place, and probably appears strange things in
the display (or not appear normal things in it :-). Be careful not to
damage the LCD, when you unglue it.

Next step. Disassemlby of the keyboard. The method that i use is cut
the plastic buttons that mantain the keyboard in its place (maybe 20
or more). The
reassembly that I do is literaly sewing it with copper wire.