Crane 490 Dead Soda Columns

MIPS

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Kamloops, British Columbia, Canada
I have been asked to investigate a problem with the vending machine at work. It is a SnackCombo unit with the eight slot refrigerated drink option. Functionally the machine runs fine for all of the non-refrigerated selections but only three of the eight drink columns work. Trying one of the non-working ones just gave MAKE ANOTHER SELECTION.
The first fault I found was that there is a 1N4148 zener on the motor board that is inline with the out-of-product switch(it failed open so the column looked to be always empty). I started replacing those on each column and testing on one of the three circuits I knew still worked. That got me seven working motor units until I came across a motor that was seized. (also reads a dead short) It took a moment to try and vend and then displayed MAKE ANOTHER SELECTION. From then on that column circuit even with the known good motor assembly was now dead. Was there a fuse I blew somewhere??
In fact, now that I had sorted that first problem I still had four columns that would refuse to work. I switched the wiring (row E became row F and vice-versa) and the dead columns moved with the cable swap so the best I could think of now was something further down the line was bad.
All the product selections connect to the "Snack Interface" (PCB P/N 1576008) before connecting to the vending controller. On visual inspection it is in excellent shape and a quick test found the capacitors were in range (changed the 10mfd 50v ones anyways) and none of the regulators, transistors or diodes were obviously bad on a diode check. Also no sign of any fuses. Should I assume one or more of the ULN2003AN's have either failed or blown?
 
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