These type of vendors use line voltage (115 volts A.C.) through the switches & the vending relay, solenoids, & other switches ( sold-out microswitch, vending gate "ready" microswitch -switch)down on the vending gate assembly. use caution as they will "bite" you,
take a good look at the vending gate assembly & check for broken brass quick connects on that columns micro-switches, as these machines are famous for brittle/corroded connectors that will snap in half for no apparent reason other than to drive you crazy!
the sold-out micro-switches are also "daisy chained" just like the section buttons as mention before, there are also some "vending gate ready" micro-switches that enable or disable will disable a particular column and give you the symptoms you've mentioned...I've seen a lot of this type of problems
you can find the female quick-connects ( which are smaller than a "standard" 1/4" quick connect) at Radio-shack. have fun!