Sharp PC-1600 keyboard issues

[tony duell]

> The PC-1600 powers on and mostly behaves normally after an "All Reset"
> but the keyboard is having trouble; here are the symptoms:

When one of my PC1500s showed similar symptoms, it was, alas, a defective
I/O pin on the I/O controller ASIC. Fortunately in the case of the PC1500 the
same I/O controller turns up in the peripherals so I took one from a dead
printer/cassette interface. 

But it would certainly be worth taking it apart and cleaning it.

> I've found the Technical Drawing set here:
> http://www.sharp-pc-1600.de/Schaltpl%8ane%20A3/Technical_Drawing_DINA3.pdf
> which makes it obvious that the dead home-row keys are related to the
> KIN3 line from the keyboard matrix; I note that the keyboard signals are
> brought to the edge of the PCB and connected to a membrane layer which
> contains additional circuitry, including what looks to be an IC that
> does the keyboard decoding.  My first guess would be dirty contact

That may well be the CPU.

> between the PCB and this membrane (esp. since the lines in question are
> close to a hole in the battery compartment where the aforementioned
> 30-year-old batteries were...) but I'm a bit nervous to disassemble and
> clean this without knowing how it's held together.  Anyone have any
> experience here? Any tips?

The exploded diagram on the last page of those schematics suggests to me 
that it is built very much like the PC1500. On that machine you take off the
battery cover and batteries and undo all the screws on the bottom. The case
separates, you unfold it on the FPC. There are a couple of brackets to remove, 
then lots of screws and the keyboard PCB just lifts out. The only gotcha is that
the key buttons are all loose in the top case so don't drop it or turn it over...

-tony


Thanks as always,
Josh