Sinclair ZX80 questions

Jules Richardson julesrichardsonuk at
Mon Aug 21 14:29:10 CDT 2006

Tony Duell wrote:
> I bought an MK14 back when it was current. That put me off Sinclair for 
> life...

Out of interest, what was so bad about them that wasn't typical of that class 
of machine around that time? Admittedly without having been involved at the 
time, it seems with hindsight that there were an awful lot of similar machines 
around that sort of era with odd design quirks, very limited power, 
poor-quality PCBs etc.

>> I was hooked... Mind you I had the same hassle with my Acorn Atom kit too,
>> many owners of expanded Acorn Atom systems will tell you of the roasting
>> regulator on their boards.
> I seem to remmember you were supposed to fit a zecond regulator (7805) 
> and cut a link if you expaneded the Atom. Then each regulator powered 
> about half of the machine.

The construction guide says: "both regulators and a heatsink should be fitted 
to all Atoms". I've never seen one with only a single regulator, but doubtless 
a few individuals building from kits tried it. The manual gives the minimal 
system with 2KB of memory as around 750mA draw, so that's within the 
capabilities of some 7805 variants and not others...

More common is that the regulators have been bypassed or removed entirely and 
an external supply is used. It's rare-ish to find an Atom with regulators and 
heatsink still intact (maybe 25% are like this).  Rarer still is to find an 
Atom using an external supply where someone's actually done as the manual says 
and indicated on the back that the machine's wired for 5V regulated input 
rather than 8V unregulated - I expect there are a lot of toasted Atoms still 
floating around!



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