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How could I make a shot clock count down without the control board?

I came across an old basketball shot clock (Nevco SCD-2, from 1987) , and upon seeing it I instantly thought of new years, It would be an epic countdown. Not to mention the immensely loud buzzer that it contains. Problem is I can't seem to get any info about how the circuitry works (the clock thing is pre-interenet).  The only input (besides power) is a small plug similar to coaxial that I assume sends some kind of pulse that is decoded on board. anybody got any ideas?

Re-design5 years ago
It might be easier to just use the numerals and build you own count down timer.
Take some pictures of the circuit board, and lets take some guesses. I SUGGEST it uses rs232 serial.

Steve