I'm IW9HGS, Gabriele "asbesto" Zaverio, and this is my ICOM IC-720A Rotary Switch Mod!
I made this mod starting from the F5IKI Rotary Switch Mod, that never worked
to me, I think because I had some problems with transistors and bad
components. So I decided to modify the mod itself, wiping out the PNP
section and the binary count logic, and using a simple 4017 CMOS counter. It
works very well and I think this schematic is simpler than the other. :)
A brief description: the counting pulse from J1-7 is "filtered" using 74HC00
NAND doors; it goes directly into the 4017, that start counting. The 4017
output goes to the 2222 transistor that drive the relay, and also goes to
the diode matrix, to form the L1,L2,L4,L8 binary code needed for the 720's
microprocessor. The 4017 is powered directly to 7.5V, so there's no need to
convert this level to obtain the binary code so the microprocessors can use
it directly (in fact, the 720 uP need about 7V logic levels. I don't know
why)
Many thanks to: F5IKI, that sent me the logic boards to do this mod and some
components; IZ2LSL for helping and supporting me and for the 1N4004 MELF
diodes; WB0GAZ, ON4AZD and udomahr@t-online.de for documentation I found on
the Internet, IRC Channel #retrocomputing on Azzurra.net for support and
happiness, the Ari Fidenza Forum for support and help, and Acme
(olocolors.org) for the LIFETIME TOOLS that really helped me a lot! ;)
Feel free to contact me at the address iw9hgs(at)gmail(dot)com, or via
QRZ.COM! ;)
