Odd QL Keyboard Problems

[RWAP]

Has anyone ever come across a QL with problems on the keyboard in the bottom left hand corner?

Basically the keyboard all works fine, EXCEPT when you use the left hand SHIFT KEY and Z, or the CTRL + left cursor key.

Both keyings work some of the time (maybe 1 in 10) - sometimes you get no characters, sometimes you just get the lower case z or the left cursor key, and sometimes you get a string of 4 characters...

Using the right hand SHIFT key with Z works as expected....

I swapped the keyboard membrane and rubber mat - exactly the same issue.

Swapped the case top of the QL and things have improved, CTRL left now works fine - SHIFT Z also works in that you always get an upper case Z, but you still sometimes get 3 or 4 repeated characters instead of 1).

I have even swapped the NEC 8409 for a Phillips 8409.

Open to suggestions!

[vanpeebles]

Could it be the socket that the ribbon plugs into? Dirty contacts etc?

[Mr_Navigator]

or dry solder joints

[Mr_Navigator]

Are you able to montor the logic signals changing, pins 1, 2 and 3 on J12 are next to each other electrically and relate to the symptoms.






Images from here https://picasaweb.google.com/1087615291 ... ReCreated#