The output of this chip is to have all the outputs high except the one being addressed, possibly for use as a low side driver for nixie tubes or something, but either way it means that when you switch to a digit you trigger a negative going pulse. Here’s what I mean: the 7442N is a BCD to decimal decoder, meaning that on the 4 bit input you can count up from 0 to 9 and for each combination a different output pin will be enables, but note I didn’t say ‘will be high’. Most strangely of all, the 7442N outputs are inverted from what the clock on the 74LS273 wants. The bottom decimal points are not controllable, but could be by bodging a copy of the top circuit on the bottom. The values are the same so the board designer wasted two resistors on those decimal points as well as the labor to install them. The 2n2222 drives the decimal point through a 470R resistor, not using the resistor pack, but the resistor pack has a spare resistor because it has 8 and the darlington only has 7. There are also a few interesting notes I have on this board design:
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