20 Aug
2006
20 Aug
'06
7:24 a.m.
Rob O'Donnell wrote:
Yep, there are five larger white plastic clips holding the case together, then
two smaller black ones for the overlay - it does indeed look like the PCB was
pre-drilled for these, so I assume that they're present even on an ZX80
without an overlay. I was just thinking that I'd rather take the machine back
to ZX80 spec, so not having extra holes drilled in things as part of the
upgrade is a bonus :-)
:-) It does seem to be the original - BASIC keywords are mapped to the ZX80
keyboard layout, whereas with the other ROM they map to the slightly different
layout of the upgrade overlay.
They look more glued 'into' the PCB though. At first I thought it was just
stray junk and was about to clean them off - but if it was like that from the
factory I'll leave them as-is :-)
That machine works, anyway, after a fashion - but I can't get a nice clear
picture on the couple of TVs that I'd tried so far, so it's possible that
there's a fault in the modulator somewhere. But it's evidently OK otherwise
and doing things as expected... (I *think* I've got a spare UM1233 somewhere
if I can find it, in which case it'll be easy to swap it in and try it)
Out of interest, anyone know how many ZX80s were sold as kits? This one's a
factory-built one, complete with original ZX80 PSU. The heatsink for the
regulator gets pretty hot, and that's even without the RAM pack plugged in...
cheers
Jules
At 13:30 20/08/2006, Jules Richardson wrote:
Thanks - not something I'd heard about before. I've had a couple of ZX81s in
the past (later ones, issue 3 and 5 I think) but never had a real look at a
ZX80 before.
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..) 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. ZX RAM packs were completely interchangeable, the
pinout, and the memory
allocations were the same.
That's good to hear!
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.
Interesting. Just whipped the lid off this one and it is DRAM as you say (8 x
4116 ICs).
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?