Keyboard Membranes Spectrum +

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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PeterJ
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Keyboard Membranes Spectrum +

Post by PeterJ »

Odd question,

Is is normal for all keys to stop working on a Spectrum + or does that signify something else other than the keyboard membrane might be at fault? I have checked the cables are plugged in!

Thanks
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Ast A. Moore
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Re: Keyboard Membranes Spectrum +

Post by Ast A. Moore »

It’s rather odd, but suggest that either the ULA’s keyboard inputs are completely dead (which is not impossible, but very improbable) or that all the diodes in the keyboard matrix have failed at once (also very unlikely).

You can eliminate the membrane from the equation by unplugging it and then running a wire between the two keyboard connectors. Just poke one end of the wire into either pin of KB2 and then poke the other end into each pin of KB1. KB2 selects one of the semi-rows of the keyboard and KB1 selects a key in each semi-row.
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

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PeterJ
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Re: Keyboard Membranes Spectrum +

Post by PeterJ »

Ast A. Moore wrote:
Fri May 22, 2020 2:52 pm
Just poke one end of the wire into either pin of KB2 and then poke the other end into each pin of KB1. KB2 selects one of the semi-rows of the keyboard and KB1 selects a key in each semi-row.
Thank you. That is an excellent idea.
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1024MAK
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Re: Keyboard Membranes Spectrum +

Post by 1024MAK »

Err, yeah, I think he means, take a piece of thin solid core wire (eg an off-cut of telephone or network cable) (with the insulation stripped off each end) and briefly connect any pin in the left hand keyboard socket and any pin in the right hand keyboard socket.

You can test if the rest of the Spectrum is alive: use a Sinclair ZX Interface 2 Interface (or other comparable joystick interface) and err, a joystick, then waggle it!

Sometimes (rarely) the problem is nothing to do with the keyboard or the ULA being faulty, but due to a memory fault causing the machine to lock up.

Mark
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