Issue 1 ZX81, some keys not working - keyboard looks ok, also RAM packs don't work

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Ravenger
Posts: 9
Joined: Tue May 11, 2021 5:27 pm

Issue 1 ZX81, some keys not working - keyboard looks ok, also RAM packs don't work

Post by Ravenger »

Hi, I've got a rather battered Issue 1 ZX81 that I'm considering restoring (I already have another fully-refurbed one I bought from Ebay)

It powers up OK, but some keys don't work - HJKL and NEWLINE.

I opened it up and checked the keyboard connectors and they look ok - no obvious breaks, so I'm not sure that getting a replacement keyboard would fix it.

Also If I connect a RAM pack to it (I know the RAM pack works) then it shows a blank screen. I've tried two different RAM packs with the same result.

Any ideas?
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BarryN
Posts: 67
Joined: Thu Nov 09, 2017 11:34 pm

Re: Issue 1 ZX81, some keys not working - keyboard looks ok, also RAM packs don't work

Post by BarryN »

Ravenger wrote: Thu May 20, 2021 4:08 pm Hi, I've got a rather battered Issue 1 ZX81 that I'm considering restoring (I already have another fully-refurbed one I bought from Ebay)

It powers up OK, but some keys don't work - HJKL and NEWLINE.

I opened it up and checked the keyboard connectors and they look ok - no obvious breaks, so I'm not sure that getting a replacement keyboard would fix it.

Also If I connect a RAM pack to it (I know the RAM pack works) then it shows a blank screen. I've tried two different RAM packs with the same result.

Any ideas?
You could test the keyboard issue by unplugging the keyboard and carefully shorting the wires that would be connected on the keyboard matrix by those keys and see if the "key presses" register. For the ram pack issue, clean the expansion connector and test the connections. A blank screen means the ram test is probably failing.
bola_dor
Posts: 277
Joined: Wed Oct 02, 2019 5:32 am

Re: Issue 1 ZX81, some keys not working - keyboard looks ok, also RAM packs don't work

Post by bola_dor »

HJKL NL is D7.
wiring-terminals.png
Test it using a thin insulated wire connecting the keyboard contacts in the board socket from the large one to any one in the smaller one. You should see the characters appear in the screen.

D7 and RAM CS lines are one near each other in the back connector. It surely is a coincidence but doble check nothing is wrong there..
Ernesto
ZX80, TK83, CZ1000, CZ1500, TK85, CZ2000, CZ1000Plus, CZ Spectrum, TK90X 16Kb, CZ Spectrum Plus, TS2068, Sinclair QL. TS 1016, TS1040. And more to come :D
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