I have a route with a USI 3015a snack machine with a Coinco BA32SA dollar acceptor.  Everything has worked pretty well over the years but about a week ago, people have been unplugging the machine because it starts making a noise like an alarm style buzzing supposedly.  I have never heard the noise myself.  I have reports that the machine will not accept dollars and change does not register on the display, which is usually blank once the buzzing starts.

When I get to it, I reset the unit (unplug, wait a few seconds, replug), try a BUNCH of test vends with dollars, coins, and multiple combinations thereof to include getting change, etc.  While I am at the machine, of course, everything works fine.  It supposedly usually takes anywhere from 4-6 hours before it fails.

A couple of the times I restarted the machine, the display showed "EXACT CHANGE ONLY" instead of my custom message.  One time, after a restart, the display froze on that "EXACT CHANGE ONLY" and I had to restart it again.  One of the times I came in and the machine was still plugged in but had failed, there was just the number 4 on the display.  I did not notice any flashing LEDs or anything else out of the ordinary inside.

I took apart the Coinco and cleaned it as best I could.  All the motors seem to be working fine.  I also checked all the connections and they seem to all be connected and tight.

The fluorescent bulb was flashing as well, but it is almost more like the bulb needs to be replaced rather than it being something associated with the issue, but what do I know.

I have checked both the manuals for the USI and Coinco without any hint as to where to go from here.

Any advice or help on this would be great!