All --
I?m finally getting around to building the JS-1 joystick replica and
using a D+7A board I got a few months ago. I have the JS built but now I?m
trying to recalibrate the board per the instructions on page 4 and I?m
having trouble getting it to read the right values.
The calibration procedure, basically, starts with putting 2.54v on an
analog input and using a short program to read the input and display it on
the front panel output port of my IMSAM. There are two problems. When
reading the A/D and displaying the input, bit7 is stuck ON. The second
problem is that I can?t get the input to read the maximum positive of 7Fh
(excluding the seemingly stuck bit7).
The version of the schematic I downloaded isn?t a very good scan, and
doesn?t seem to be the same revision as my board (because the adjustment
pots have different reference numbers). There are a few common chips that
touch bit7 (like the LS367) which I can swap, but the others, like the
AM2502 successive approximation converter, isn?t as common.
So before I go swapping chips, does this board have any common failure
mode I should be looking for?
Thanks!
Rich
--
Rich Cini
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator
http://www.altair32.com
http://www.classiccmp.org/cini