Master 128 keyboard odd problem

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MikeKee
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Master 128 keyboard odd problem

Post by MikeKee » Sun Sep 16, 2018 3:10 pm

Hiya all.

Long time no post, and when I do it's usually about my Elk.

However,I got hold of a Master 128 and it has a keyboard problem: the Caps Lock, Num Lock work fine (toggling the lights) and CTRL+BREAK will beep and reset. However, none of the other keys work at all, nothing appears on the screen.

Any ideas?

Cheers

Mike

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AndyF
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Re: Master 128 keyboard odd problem

Post by AndyF » Sun Sep 16, 2018 3:46 pm

Assuming the keyboard connector is correctly positioned (I only mention this as I had one once where it was not!) , is it the later/rare? 'membrane' type keyboard ?

These afaik are more likely to fail as the membrane 'flat thing' is the same type of thing used in Amstrads, Spectrums etc. You'll know if it is by the key depression feel, it will not feel anything like any other Elk/Beeb keyboard at all.
Andy

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Coeus
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Re: Master 128 keyboard odd problem

Post by Coeus » Mon Sep 17, 2018 7:07 pm

MikeKee wrote:
Sun Sep 16, 2018 3:10 pm
However,I got hold of a Master 128 and it has a keyboard problem: the Caps Lock, Num Lock work fine (toggling the lights) and CTRL+BREAK will beep and reset. However, none of the other keys work at all, nothing appears on the screen.
That's odd. Faults affecting individual keys are common, either from defective switches, defective solder joint, or breaks in the tracks near the switch due to flexing over time. Also, as the keys are arranged in a matrix, a fault on one row or column can leave a whole set of keys not working but that is not normally the whole keyboard except for a couple of keys.

The break key is unusual because it is actually "reset" to the processor and not part of the normal key matrix at all. Normally shift and ctrl are also a little odd because there are on a special row that does not generate an interrupt to the processor. Instead, when the OS processes one of the other keys it checks the state of shift/ctrl to see which code to generate.

Inspecting the circuit diagram might be a next useful step.

tom_seddon
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Re: Master 128 keyboard odd problem

Post by tom_seddon » Mon Sep 17, 2018 7:18 pm

Could there be a ROM that's doing *FX2 1 (select RS423 input) on startup? - when I do *FX2 1 on my Master, the keyboard apparently stops working, but CAPS LOCK and SHIFT LOCK still do their its thing.

If you do T+BREAK, you should get the tape filing system selected, which I think is something that's sorted out before any ROMs initialise, so the keyboard should still be usable at that point.

--Tom
Last edited by tom_seddon on Mon Sep 17, 2018 7:20 pm, edited 2 times in total.

Coeus
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Re: Master 128 keyboard odd problem

Post by Coeus » Mon Sep 17, 2018 7:26 pm

tom_seddon wrote:
Mon Sep 17, 2018 7:18 pm
Could there be a ROM that's doing *FX2 1 (select RS423 input) on startup? - when I do *FX2 1 on my Master, the keyboard apparently stops working, but CAPS LOCK and SHIFT LOCK still do their its thing.
That's an interesting idea. It had crossed my mind that the issue might be further down the line and not in the keyboard but well done for working out how that might happen.

I thought T-Break was actually for the Teletext adapter and Space-Break was cassette but the principle holds good. If you can change filing system with other keys held down at break (D for DFS, A for ADFS etc.) that would prove the keyboard works.

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