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zx80 clone which is the best most accurate?
Posted: Fri Jun 22, 2018 1:10 pm
by cypher007
thinking of building a zx80 clone, preferably from a kit. I have a 3D printer so can print a case.
ive seen some by eastern European developers and others. just wondered whats the best bet?
are original zx80's still crazy money? any non working ones worth buying and repairing? as I have probably enough knowledge to get it running.
Re: zx80 clone which is the best most accurate?
Posted: Fri Jun 22, 2018 3:38 pm
by 1024MAK
There is/was an exact copy of the PCB that was available. You can't get better compatibility than that! Have a look at Grant's wonderful site
here 
In reality, the only difference between a modern clone of a ZX80 and the real thing, is the RAM will be a modern CMOS SRAM chip instead of the old 2114 SRAM chips. The ROM may be a modern CMOS EPROM chip. And the 74 series 'TTL' may be the CMOS 74HCT versions (unless that design uses programmable logic chips). Normally, none of this makes any difference with regards to compatibility.
It's the ZX81 clones that may have slight differences, as different people make slightly different implementations of the replacement logic for the ULA. Or add extra functionality/features.
Yes, real ZX80 machines still go for silly prices on eBay and similar sites. Even if they are non-working, but look good. The only cheap-ish ZX80s are non-working machines that are in a cosmetically poor condition.
Mark
Re: zx80 clone which is the best most accurate?
Posted: Fri Jun 22, 2018 11:58 pm
by mhudson52
I am waiting on the arrival of the reproduction kit sold by Oricfan on Ebay. From what I understand it is based on Grant's design with a couple of corrections made so there should be no issues with compatibility.
Has anyone else on the group built one of his kits before?
Re: zx80 clone which is the best most accurate?
Posted: Sat Jun 23, 2018 12:23 am
by 1024MAK
Is he the guy who did the Jupiter Ace kits? [see
this thread].
If yes, then Phill (Prime) has. I have also.
Mark
Re: zx80 clone which is the best most accurate?
Posted: Sat Jun 23, 2018 12:56 am
by mhudson52
Yes, it is the same guy (Plamen) who did the Jupiter ACE. Hopefully my experience will go as well as yours and Phill's, assuming everything was to your satisfaction.
I can 3D print my own case, but maybe this will get me motivated to get back to work on my vacuum forming project. I have the decal files and water slide printing sheets to make it look nicer.
If everything with the kit is as it should be, I will probably scan the board before any soldering commences in case anyone should want a copy of it.
Re: zx80 clone which is the best most accurate?
Posted: Sat Jun 30, 2018 11:26 am
by cypher007
cheers guys. found some old listings on ebay for it. but no new ones.
im just wondering whats wrong with this original one:
https://www.ebay.co.uk/itm/Sinclair-ZX8 ... SwRNRbH5No
seems cheap for an original.
Re: zx80 clone which is the best most accurate?
Posted: Sat Jun 30, 2018 2:30 pm
by 1024MAK
Looks like a fairly typical example of a ZX80 to me.
The dark, low contrast TV picture is normal when the colour TV used relies on the back porch part of the TV signal to define the black level. As the ZX80 does not produce this part of the signal, the colour TV calibrates itself incorrectly.
Should work fine on a monochrome/ black and white TV, or on a colour TV that can cope with the signal.
Mark