After a successful run with the 380Z RM released this, a smaller cassette based
machine built round the 4 mhz Z80A processor with 32k of memory. Originally
produced in a black steel case (apparently the tool used to make the plastic
cases was dropped!) with a 40 character TV interface, it was later expanded
to have an 80 column monitor output and 64K RAM. Once the moulding problems had been sorted
the white plastic cased version was released, and by this time there was also
a hi-res add-on card that allowed colour output - the original was monochrome
only. The only peripheral I can remember being released was a floppy drive even
though the base hardware wasn't designed for one - in CBM style all comms were
done using a high speed serial link.
This was the last Z80 machine RM produced; the followup was the high-spec PC-186.
When I got this machine I thought it had been cannibalised and wasn't happy poking
around with PSUs so I left it alone. Cut to 2017 and there had been chat on a collector's mailing list about the necessary voltages
and they matched some new PSUs I'd bought for anything that had 4116 DRAMs in, ie needed +5V, +12V and -12V.
After reassembling I tested the PSU and was surprised to see it was good, just needed the output adjusting.
The ROMs were OK so I cleaned and reseated the socketed chips and.... it NEARLY worked.
The Z80 was running, the boot ROM was being selected and there was CAS and RAS at each RAM chip.
Black flickering screen output though. Looking at the schematics for the video circuit it reminded me of the
Grundy Newbrain, it was easy to trace backwards from the
input to the modulator and test all the video generating chips on the way with my new BitScope Micro -
a handy portable oscilloscope and logic analyser. It showed that the video output from a 74LS166 shift register was missing -
all the inputs were good and the truth table on the datasheet showed there SHOULD be an output.
Whip it off with the desoldering station, fit a socket and new LS166 and we're in business!