28 Mar
2002
28 Mar
'02
3:33 p.m.
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
The text
refers to 2x2114 or a 4118 installed in the UK version and a
2K option for export - possibly there are 2 versions of the board?
OK, I've pulled my ZX81 apart. The PCB claims to be 'Issue 1'. So, fit L2 if you install a 6116 (A10 on pin 19). Fit
L1 if you install a
4118 (I am not sure what pin 19 is, I can't find a
4118 data sheet, but
at least one schematic I have calls it 'E', presumably an active high
enable signal). Fit either or no links if you install 2 * 2114s. Never
fit both links, or you'll short A10 to the +5V rail.
Today I checked out about two dozen ZX81/TS1000s. They've been piling up
in a box and today I finally got to them. Here's what I found:
All of the 1K boards had two 2114s and no jumper installed.
All but one of the 2K boards had a single 2016 and L2 was installed.
One 2K board had a 6116 and L2 was installed. The board was operational
and appeared unmodified.
I replaced a socketed 2016 on a working board with the 6116 pulled from the
above-mentioned board,
and the board still worked.
So I think it's safe to say that L2 is required for a single-RAM-chip
board, and that a 6116 is a drop-in replacement for a 2016.
Never did see a 4118. Perhaps the use of it would change things,
jumper-wise.
Glen
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