Hi all
Plugged my ZX81 in and it is pulling from the bottom and cant see the text but something seems to move when a key is depressed is this a sign of a faulty ULA.
Many Thanks
Sinclair ZX81 is this a ULA issue
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Re: Sinclair ZX81 is this a ULA issue
That looks indeed like an ULA issue.
- 1024MAK
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Re: Sinclair ZX81 is this a ULA issue
Is this via the TV/RF/UHF output? Sometimes some TVs just don’t like the output from the ZX81. If the TV has fine tuning, see if you can adjust it. If you have another TV, try that.
And yes, it could also be a problem with the ULA or with the ceramic resonator (this is used to control the master oscillator in the ULA, it is used for all the timing including the timing for the video generation).
Mark
And yes, it could also be a problem with the ULA or with the ceramic resonator (this is used to control the master oscillator in the ULA, it is used for all the timing including the timing for the video generation).
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.
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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- Posts: 30
- Joined: Sun Apr 11, 2021 5:31 pm
Re: Sinclair ZX81 is this a ULA issue
Is that the tiny capacity linked to pin 35 on the ULA?
- 1024MAK
- Posts: 5103
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Sinclair ZX81 is this a ULA issue
The identification on the silk screen printing on the board is ‘X1’, it looks like a rectangular capacitor, but it has three legs/pins. One two pins are electrically connected on the board, one goes to 0V/GND. the other connects to capacitor C6, and then C6 connects to pin 35 on the ULA.
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.
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.