I started on my new ZX-81 replacement board (kit) ZX81+38

Discussions about Sinclair ZX80 and ZX81 Hardware
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mahjongg
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by mahjongg »

Finalized the PCB
Image

also uploaded production files to github:
https://github.com/mahjongg2/ZX81plus38 ... LICENSE.md

more pictures here:
https://revspace.nl/ZX81plus38_simple_t ... s_finished
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1024MAK
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by 1024MAK »

👍 8-)

Mark
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by McKlaud »

Looks great and thank for sharing.
Claudius
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GTS1000TX
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by GTS1000TX »

This looks very cool. Some Atari folks designed new boards for Its 8bit line. I wanted to build one, but could not justify the expense. Was going to be over $500 to build one myself. The wife would kill me. But this appears more affordable. And I just happen to have a Timex Sinclair 1000 that may have a bad PLA chip. Looking forward to your bill of materials list.
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marste
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by marste »

@mahjongg very very nice project, compliments!

regarding jumpers, would it be nice to have one switching from the 4k ZX80 ROM to the 8k ZX81 one (and also slow mode)?
(with the 16kbyte ROM both fit at the same time and is a matter of switching just address bit 13)
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mahjongg
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by mahjongg »

The latest version (the one uploaded to GitHub) has exactly those jumpers, on the bottom side, so you can still change them even after soldering in a ROM socket. And yes, one of the jumping options is to use the old original ROM, the default is to use a modern OTP, in 8 and 16K variations.
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mahjongg
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by mahjongg »

Due to corona, I still have not built a prototype board myself, but in the meantime several people are trying to get their version working, and a few small errors have cropped up. The main problem is that two address lines (A13 and A14) on the expansion connector have switched, so I have to repair that with a PCB revision, but unless you want to use an expansion device, like a printer, or sound device, or something like that, it probably won't matter.
Also I have found that I made a mistake in the footprint of the RCA connector, if you try to use the RCA connector in the BOM, you will find that the plug points inwards, instead of outwards. This solvable by using a slightly different (more simple) RCA connector, the CLIFF FC68391.
I hope to receive a PCB and some parts soon, so I too can start building a prototype, even though my makerspace is in partial lockdown, and I must be careful with money, as my company has fired me (with lack of work and covid as an excuse). and I have still a couple of years to go before my pension.
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mahjongg
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by mahjongg »

in the meantime I have made a new layout and am now at revision 1,6, Details can be found at GitHub, and at www.revspace.nlm in the projects section.
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1024MAK
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by 1024MAK »

Thanks for the update :D

Sorry to hear that you have been made redundant. I hope you are able to cope and I wish you good luck in the hunt for a good new job.

Mark
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mahjongg
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Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Post by mahjongg »

Thanks Mark. I'm managing...
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