A problem my new keyboard

[frontenac]

Hello, everyone.

I'm writing to you today since my understanding of electronics is insufficient to fix my problem.
I discovered computers on a ZX81, and it was a pleasure to rediscover this fantastic machine.

I upgraded it with a VLA81, composite mod, and ZXPAND+.
I then had the wild idea of adding a physical keyboard (thanks, Adam, for the PCB - https://www.pcbway.com/project/sharepro ... 46a1b.html ; you did an excellent job).
I wired this keyboard straight to the ZX81 motherboard.
It works almost perfectly.

When my new physical keyboard is not connected, the original keyboard operates normally.
BUT,
when I use the new physical keyboard and CONNECT the ZXPAND+, I no longer have access to SHIFT-S, SHIFT-D, SHIFT-F, and SHIFT-G
(but the keys “SHIFT, S,D,F and G” are working normally).

I don't understand my mistake.
Do you know what is wrong?

Thank you for your time!
David

[1024MAK]

when I use the new physical keyboard and CONNECT the ZXPAND+, I no longer have access to SHIFT-S, SHIFT-D, SHIFT-F, and SHIFT-G
(but the keys “SHIFT, S,D,F and G” are working normally).

Some questions:
Do you mean SHIFT-S, SHIFT-D, SHIFT-F, and SHIFT-G don't work on the ZX81 membrane keyboard, don't work on the new keyboard or don't work on either keyboards.

What happens if the membrane keyboard is disconnected?

Mark

[frontenac]

hello there!
i have made some more testing...
Then i dicovered that it's not related to the zxpand+ board.

SHIFT-S, SHIFT-D, SHIFT-F, and SHIFT-G don't work in both keyboards when they are connected together at the same time.
"LPRINT, SLOW, FAST and LLIST" works with the membrane keyboard when i unplug my physical keyboard.

Something is sadly not working with my project

David

[1024MAK]

It may be extra stray capacitance. Hence my questions earlier.

Mark