Non working ZX81

Discussions about Sinclair ZX80 and ZX81 Hardware
colday
Posts: 25
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday »

Anyone able to confirm if the readings I posted are accurate?
I have many 8 bit computers.
8x BBC's, 4x Amstrads, an Electron, a C64 and...
4x ZX spectrum rubber key and...
2x ZX81's.
Plus some 8bit consoles...
colday
Posts: 25
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday »

I guess not then. Ok, no worries. I'll figure something out.
I have many 8 bit computers.
8x BBC's, 4x Amstrads, an Electron, a C64 and...
4x ZX spectrum rubber key and...
2x ZX81's.
Plus some 8bit consoles...
User avatar
1024MAK
Posts: 5101
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Non working ZX81

Post by 1024MAK »

colday wrote: Mon Oct 14, 2019 8:12 pm I guess not then. Ok, no worries. I'll figure something out.
Sorry, I’m rather busy at the moment (work). I got up at 07:00 this morning for a meeting in city far from home. And have just got on the train home. I’m also rather busy for the rest of the week.

If you don’t have an answer by the weekend, I’ll try to find time to connect my oscilloscope up to a ZX81 and post up an image of the waveform and take some voltage readings with a multimeter.

The signals on these pins are high frequency DC pulses, so the actual results depends on the type of multimeter used.

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.
colday
Posts: 25
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday »

Thanks Mark.

It's appreciated as I really want to get this zeddy up and running.

Quite frustrating when it's just sitting there and I have no idea what to do next.

Is there a document anywhere with specs for the ULA and PIN outputs etc?

I'm thinking I may create one if not as would be useful for reference.
I have many 8 bit computers.
8x BBC's, 4x Amstrads, an Electron, a C64 and...
4x ZX spectrum rubber key and...
2x ZX81's.
Plus some 8bit consoles...
User avatar
mrtinb
Posts: 1906
Joined: Fri Nov 06, 2015 5:44 pm
Location: Denmark
Contact:

Re: Non working ZX81

Post by mrtinb »

I was given this page from a forum member:

https://www.worldofspectrum.org/hardware/rep3.html
Martin
https://zx.rtin.be
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
colday
Posts: 25
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday »

Martin.

A quick scan read and that looks good. I shall have a bit more of an in depth read. Thanks muchly!

Edit: So having read it, it looks like I need a logic probe...

More expense.

Can I grab a cheap one from China? Or should I look at buying a branded one?
I have many 8 bit computers.
8x BBC's, 4x Amstrads, an Electron, a C64 and...
4x ZX spectrum rubber key and...
2x ZX81's.
Plus some 8bit consoles...
User avatar
mrtinb
Posts: 1906
Joined: Fri Nov 06, 2015 5:44 pm
Location: Denmark
Contact:

Re: Non working ZX81

Post by mrtinb »

I bought the cheapest from China.
Martin
https://zx.rtin.be
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
colday
Posts: 25
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday »

mrtinb wrote: Wed Oct 16, 2019 9:49 pm I bought the cheapest from China.
:D
I have many 8 bit computers.
8x BBC's, 4x Amstrads, an Electron, a C64 and...
4x ZX spectrum rubber key and...
2x ZX81's.
Plus some 8bit consoles...
User avatar
1024MAK
Posts: 5101
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Non working ZX81

Post by 1024MAK »

A post with a useful collection of pin outs (including Z80, ULA, ROM, RAM) for ZX81s is linked to in my sig. below...

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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