The chips used on Andrew Kay's 3174 interface board are no longer in production; they must be procured through sources like eBay. Any chip you buy is either NOS or removed from equipment after use. I bought mine as NOS.
The DS8340 chip has noticeable grey oxidation on the pins of the chip. When I soldered the chips onto the PCB I visually checked every connection to see a bright properly formed solder surface, using a stereo microscope. However, when I tested connectivity I found that the +5V pin of that chip, while appearing to be soldered properly, was not in fact connected to the rest of the board. The oxide on the pin left a thin insulating area around which the solder flowed.
I used some flux and resoldered the pins to make sure I had a good connection, after which I went back to testing.
VERIFYING THAT SOFTWARE ON LAPTOP AND INTERFACE BOARD ARE COMMUNICATING
Andrew provides a simple script that issues a reset to the interface board. This produces a message back from the board giving the software version number. That worked fine.
VERIFYING THAT WE CAN TALK TO THE 3178 TERMINAL
Alas, when I then tried to run other example scripts, such as to read the terminal ID string or to poll the terminal and see its response, the software again failed with an 'invalid message request' error.
NEXT STEPS
I need to start probing the interface board, using my oscilloscope, to make sure I am seeing reasonable things occurring. This includes monitoring the coax connector signal and even the crystal oscillator that produces the clock for the chips.
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