Non working ZX81

Discussions about Sinclair ZX80 and ZX81 Hardware
colday
Posts: 13
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday » Sat Oct 12, 2019 8:28 am

Anyone able to confirm if the readings I posted are accurate?

colday
Posts: 13
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday » Mon Oct 14, 2019 8:12 pm

I guess not then. Ok, no worries. I'll figure something out.

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Non working ZX81

Post by 1024MAK » Mon Oct 14, 2019 11:09 pm

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

colday
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Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday » Wed Oct 16, 2019 9:19 pm

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.

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mrtinb
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Re: Non working ZX81

Post by mrtinb » Wed Oct 16, 2019 9:27 pm

I was given this page from a forum member:

https://www.worldofspectrum.org/hardware/rep3.html
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

colday
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Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday » Wed Oct 16, 2019 9:43 pm

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?

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mrtinb
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Re: Non working ZX81

Post by mrtinb » Wed Oct 16, 2019 9:49 pm

I bought the cheapest from China.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

colday
Posts: 13
Joined: Sun Aug 18, 2019 8:28 pm

Re: Non working ZX81

Post by colday » Wed Oct 16, 2019 10:05 pm

mrtinb wrote:
Wed Oct 16, 2019 9:49 pm
I bought the cheapest from China.
:D

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1024MAK
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Re: Non working ZX81

Post by 1024MAK » Thu Oct 17, 2019 12:15 am

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

Mark

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