The Sinclair QL Forum

There is continuity between those pins on mine, too, so that's probably ok. Mine did work when I last checked (just not all keys).

Do you have 2x socketed HCF4066BE chips on the component side? I suppose you could re-socket them and check they are clean. There is a single electrolytic cap too, that you can also check. The rest is resistors and diodes. I just found another couple of cracked solder joints on mine.

Yes, I have those ICs which I have cleaned and reseated. I will replace the capacitor tomorrow.
I have noticed that all the keys show continuity between the top pin and bottom left. However, keys 5 & 6 on the numeric keypad show continuity between all three points. Is that correct behavior?

With them not depressed? No, they shouldn't all be shorted if the key isn't pressed. Stuck keys could well be the issue I imagine. Remove those 2, see if it then works.

Chr$ wrote: Wed Apr 05, 2023 8:09 pm With them not depressed? No, they shouldn't all be shorted if the key isn't pressed. Stuck keys could well be the issue I imagine. Remove those 2, see if it then works.

Yes, with the keys not depressed. I realized I made a mistake. The top and bottom right (not bottom left) all show continuity but with those two, there is continuity between all three.

I will attempt to remove those two keys...

I have now removed a total of 6 keys that exhibited the strange behavior of showing continuity between all three points...Unfortunately, it has made no difference at all.

I am now considering removing them all and replacing them with better key switches.

Chr$ wrote: Tue Apr 04, 2023 9:29 pm They have a ribbon cable coming out of them with a long flat PCB at the other end that just plugs into the 2 k/b connectors on the QL motherboard. I have one and have replaced all the keyswitches with clicky ones (available new, brand Futaba).

Would you mind posting a link for the Futaba key switches you used?
Thanks

These (clicky upgrade):

https://www.pollin.de/p/futaba-eingabet ... tch-420905

Or these if you want original non clicky:

https://www.pollin.de/p/futaba-eingabet ... f-n-421526

Chr$ wrote: Fri Apr 07, 2023 11:06 am These (clicky upgrade):

https://www.pollin.de/p/futaba-eingabet ... tch-420905

Or these if you want original non clicky:

https://www.pollin.de/p/futaba-eingabet ... f-n-421526

Thank you.
I attempted to purchase and was told they don't ship to the UK
I will look for an alternative supplier.

I can forward them on. I bought 100 (clicky) and also have 11 spares. Thought it would be a good idea to keep some spares as you never know how long they will be available. They were the only source I could find.

Chr$ wrote: Fri Apr 07, 2023 11:40 am I can forward them on. I bought 100 (clicky) and also have 11 spares. Thought it would be a good idea to keep some spares as you never know how long they will be available. They were the only source I could find.

That's very kind of you, I was going to buy a 100 too so I can replace all the key switches.

However, I am not convinced my problem is the keyswitches as I tested them desoldered from the board and they worked as expected: a contact between the top and bottom right pin when depressed.