Sometimes Screen lifts up when pressing keys

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AmintaSpectrum
Posts: 18
Joined: Tue Jul 04, 2017 12:12 am

Sometimes Screen lifts up when pressing keys

Post by AmintaSpectrum »

Hi all.

This is a problem I’ve got with several Zx81 of mine. If a press some keys, sometime the screen ‘lifts up’ showing this horizontal black line. If i reposition slightly the video cable the problem temporary goes off and then goes back.

This happens either with composite mod, either without. I’m mounting vla81 as Ula.

Thanks in advance,

Davide
7A425EEE-9DDF-4158-8219-ED45847C1B8F.jpeg
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BarryN
Posts: 151
Joined: Thu Nov 09, 2017 11:34 pm

Re: Sometimes Screen lifts up when pressing keys

Post by BarryN »

AmintaSpectrum wrote: Sun May 23, 2021 8:12 pm Hi all.

This is a problem I’ve got with several Zx81 of mine. If a press some keys, sometime the screen ‘lifts up’ showing this horizontal black line. If i reposition slightly the video cable the problem temporary goes off and then goes back.

This happens either with composite mod, either without. I’m mounting vla81 as Ula.

Thanks in advance,

Davide

7A425EEE-9DDF-4158-8219-ED45847C1B8F.jpeg
Something is loose. Do you have an expansion plugged in?
AmintaSpectrum
Posts: 18
Joined: Tue Jul 04, 2017 12:12 am

Re: Sometimes Screen lifts up when pressing keys

Post by AmintaSpectrum »

No expansion, same problem on several Zx81, can be the Philips Monitor?
bola_dor
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Re: Sometimes Screen lifts up when pressing keys

Post by bola_dor »

Just to check... be sure you are not in FAST mode..
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1024MAK
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Re: Sometimes Screen lifts up when pressing keys

Post by 1024MAK »

AmintaSpectrum wrote: Sun May 23, 2021 9:48 pm No expansion, same problem on several Zx81, can be the Philips Monitor?
Definitely worth trying different cables and a different monitor/TV.

Mark
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AmintaSpectrum
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Joined: Tue Jul 04, 2017 12:12 am

Re: Sometimes Screen lifts up when pressing keys

Post by AmintaSpectrum »

How could I switch between SLOW and FAST mode?
bola_dor wrote: Mon May 24, 2021 1:27 am Just to check... be sure you are not in FAST mode..
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1024MAK
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Re: Sometimes Screen lifts up when pressing keys

Post by 1024MAK »

The default on switch on for a ZX81 is SLOW mode, also known as compute and display.

To switch to FAST mode, use the FAST function on the F key. In this mode the machine will only produce a video picture when it is waiting for user input just like how the ZX80 works. If it is running a program, the display will blank (normally to black on a CRT display). The advantage is that the program runs much faster.

To return to SLOW mode, use the SLOW function (on the D key).

Note that the setting IS NOT retained between resets/power off/on, so a ZX81 will always start up in SLOW mode.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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