Sharp PC-1600 keyboard issues

Josh Dersch derschjo at
Sat Feb 7 13:53:33 CST 2015

On 2/7/2015 11:07 AM, tony duell wrote:
>> 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:
>> 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...

I'm more concerned about disconnecting the membrane from the PCB (the 
PCB is on pg. 41/42, the membrane on 45/46 -- you can see on the lower 
edge the connections made between the two) as I'm not sure how the two 
are held together -- there's a metal bracket on top that sandwiches the 
two together (and is screwed into the "front" of the machine -- see 
parts 20/21 on the exploded disassembly).  I'm afraid if I take the two 
apart I may never get them back together making good contact again.  
Have you dealt with anything like this? Anything I should be concerned 


> -tony
> Thanks as always,
> Josh

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