20 Aug
2006
20 Aug
'06
4:59 a.m.
At 13:30 20/08/2006, Jules Richardson wrote:
Is this a machine that's been subjected to a
ZX81 upgrade kit or something? I wasn't aware that such a thing existed.
Yes. Keyboard overlay and new ROM was common
about the time the ZX81 came out, for all those
who had just stumped up ?100 for the ZX80 (there
was only a year between them..)
I have a ZX80 with ZX81 ROM but sans
overlay... (It actually is a ROM for a ZX81, and
works fine with the exception of 'SLOW' (i.e., no
flicker) mode. The hardware is basically the
same. (And no ZX80 ROM that I can find..)
Now, the keyboard overlay's actually removable,
revealing a pristine original ZX80 legend
underneath. However, two black press-fittings
attach it to the PCB at the corners of the front
edge - are these press fittings there on all
ZX80s, or have these been added in order to secure the overlay in place?
Without getting mine out and checking, ISTR that
the ZX80 came with a plastic push-plug thingy at
each case corner to hold it all together. If you
have just just this, going through the corner of
the keyboard PCB and locking it to the case
underneath, then it's probably original.
The machine came with a "ZX 16K RAM" module
(red
lettering) which I assume is later and more in
keeping with a ZX81? Separately though I do have
a module marked as "ZX80 16K Byte RAM Pack"
(white lettering). Question is, are they
interchangeable and the lettering was altered -
or does the ZX80 variant map memory to a
different location than the later red-lettered
type? (I'm assuming that the expansion bus
pinouts didn't change between ZX80 and the later machines!)
ZX RAM packs were completely interchangeable, the
pinout, and the memory allocations were the
same. I think ROM mapped to 0-16K, RAM at 16K+
The "original" RAM pack for the ZX80 was a thin
affair in the same construction (plastic covers
either side of a small PCB with push pins to hold
together) which held up to six socketed
2114's. You could buy in various memory
configurations, and add the extra 1K, 2K or 3K as required yourself.
The 16K RAM packs I think only came out at the
time of with ZX81 and were dynamic RAM. (The
originals were all static.) I think Sinclair
branded 'ZX80' (rather than ZX or ZX81) packs are
quite rare, as the ZX81 ones worked just
fine. There were lots of third party RAM packs
aimed at the ZX81. - I had a 32K one, plus an
extra ROM board that gave me lots of fancy
alternate graphic characters.. (mapped to the
8K-16K region, in place of a mirror of the system ROM)
I've also got a ROM marked as: "ROM contents
copyright 1980 Sinclair Research Ltd" - is this
the original ZX80 ROM (and the ROM in the
machine is an upgrade), or is this likely something else entirely?
Highly likely that it's the original ZX80 ROM ... try it!
Curiously there are a few stray fibres glued to
the underside of the PCB - presumably these are
a left-over of cheap PCB manufacture and
Sinclair's horrible quality control! :-)
no idea; never had mine apart that far .. It may
be whomever upgraded it had it apart at one point
too, and these got picked up then?
Rob