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Both shift keys have stopped working

Posted: Thu Nov 17, 2016 7:35 pm
by bsdnazz
so I'm assuming there's a hardware fault in the keyboard.

The CAPS LOCK and SHIFT LOCK keys work as expected but when I press SHIFT-A I get nothing which A gets me an A or a depending on the state of the CAPS and SHIFT LOCK keys.

Power to the motherboard is fine and the problem happens when cold or after running for a while.

Any obvious things I should check?

Re: Both shift keys have stopped working

Posted: Thu Nov 17, 2016 8:02 pm
by CMcDougall
do you have another beeb /keyboard working at hand? if so swap to confirm.

funny both Shifts are gone :? , might just be bad luck, so batter them 100x, then it will (or one) will work.
then it is the keyswitch/s need a good clean out, so take to bits and scrape the brown/black gunge off.

also try cleaning or take off/on the keyboard ribbon connector....

Re: Both shift keys have stopped working

Posted: Thu Nov 17, 2016 11:02 pm
by bsdnazz
I'll be going back into the loft to get the other, older Beeb to do a keyboard swap at the weekend I think.

I did also reseat the keyboard cable a good few time. More mechanicals at the weekend too.

Re: Both shift keys have stopped working

Posted: Mon Nov 21, 2016 8:18 pm
by bsdnazz
A different (not new but older with the DIP switches) keyboard works fine so it looks like I have a keyboard fault on the B+64's keyboard.

With the faulty keyboard when I power on the Beeb there's the usual start up beep and the cassette led comes on. There's a short pause and then a constant beep which stops very shortly after pressing 3 (no fewer) keys on the keyboard.

Testing various combinations of the CAPS LOCK and SHIFT LOCK keys gets the following results (and not just for the A key):
  • CAPS LOCK off; SHIFT LOCK off
    • A key generates lower case a
    • Shift A generates nothing and the cursor does not move
  • CAPS LOCK off; SHIFT LOCK on
    • A key generates upper case A
    • Shift A generates upper case A
  • CAPS LOCK on; SHIFT LOCK off
    • A key generates upper case A
    • Shift A generates upper case A
  • CAPS LOCK on; SHIFT LOCK on
    • Not valid as the two keys toggle each other
Any thoughts as to what might be wrong with the keyboard?

Re: Both shift keys have stopped working

Posted: Mon Nov 21, 2016 9:55 pm
by bsdnazz
It might just be lack of use.

Looking at the keyboard schematic I looked at which horizontal and vertical scan lines the shift keys are on and tried other keys on those lines. They mostly worked but were not perfect - not every key stroke registered. I've been trying various combinations and things are improving. Right now even the shift keys are working.

The keys are now working pretty reliably except for the ESCAPE key which might have had a hard life.

Perhaps it's the Beeb's way of asking for more attention!

Re: Both shift keys have stopped working

Posted: Mon Nov 21, 2016 11:31 pm
by 1024MAK
The Beeb keys just like a good bashing :lol:

Mark