ZX81 upgrade for ZX80

[Pierre]

I have 2 ZX80s of which both were upgraded with a ZX81 ROM and fitted with the ZX81 keyboard overlay. The one I got with the original ROM and converted it back to original and the other I kept with the upgrade. Is it worthwhile to keep it in the upgraded state or should I get the other also back to original? The other question is would there be a market to sell the ZX81 upgrade ROM and keyboard overlay. I also have the original 3KB RAM pack and a ZX80 16K RAM pack. The 16K one has ZX80 printed on it, the first one I have seen as they normally does not state ZX80 on the RAM pack. I can only assume that it was in the beginning of the ZX80s. The 16K RAM pack is faulty, but it look like standard issue 1 model, so I presume it will be one or more of the 4116 chips. The voltages test all OK.

Pierre

[RWAP]

The ZX80 is worth substantially more in its original state = ie without the zX81 overlay (sheet of plastic?) and ZX81 ROM, but the problem is having an original ZX80 ROM to put back into it.

You can use an EL-2364 Flash EPROM (we sell these for £15 plus postage with the ZX80 ROM on it) but that is not original, so may impact the value to collectors.

The overlay and ROM upgrade etc does have a value more as a collectors piece, so is worth listing on its own - you should supply it with the upgrade instructions and the ZX81 manual.

I have today sent one of these upgrade ROMs to SirMorris, so he can check if there is any difference between that and the actual ZX81 ROM - does anyone know?

[poglad]

No idea, sorry. What kind of material is the keyboard overlay made out of? Is it just paper?

[1024MAK]

I wonder if the upgrade ROM has the same bug as the first ("old") ZX81 ROM...

Mark

[sirmorris]

Soon find out..

[Moggy]

I wonder if the upgrade ROM has the same bug as the first ("old") ZX81 ROM...

Mark

As it was released before or at the same time the bugged 81's appeared it's a good bet that the sqrt bug is there, I can't see Sinclair releasing " good rom" upgrade for the 80 then klutzing it for the 81.

Besides according to maths guru Frank O'Hara even the new rom doesn't hold its FP numbers correctly.
ftp://ftp.worldofspectrum.org/pub/sincl ... 600025.jpg

A simple bit of basic seems to confirm this.

10 PRINT 1/2
20 IF 1/2 = .5 THEN PRINT "SUCCESS"
30 IF 1/2 <> .5 THEN PRINT "FAILED"

[poglad]

Ah... the days when Sinclair magazines actually contained some real meat.

[sirmorris]

I can confirm that the upgrade ROM is identical to the original ZX81 unimproved ROM as available here!