Snack machine wiring issue

[divot]

I have a snack machine where 3 of the shelf's are acting like the home switches are bad- on all selections.

Shelves E F and G. 

I would be surprised if all the switches went bad at the same time. I look at schematic and do not see a common connection for just those 3 shelves. Has anyone had this issue before or an idea where to start troubleshooting. When I test vend any of those selections it does set a fault. I will get and share those asap .

 

 

[divot]

It did not have any diagnostic error codes for those shelf's but it does beep 3 times after I attempt to vend each one. So the VMC does seem to acknowledge it did not receive the home switch signal. 

[AZVendor]

There is one common wire to every motor on a shelf which is the wires you see coming out of the combo driver board.  They go down through every motor and then terminate in the main logic board.  I would say the home switches are likely to be the horizontal wires in the diagram coming from your logic board.

[divot]

Thanks for your help. I was curious which was the switch wire. 

I am thinking the connection between the last working shelf and the first non- working shelf - has a bad / loose harness  connection, the shelf selections seem to be daisy chained together.

All motors are still spinning. So, must still have a connection from each wire. Though, I am guessing the control board looks for a lower ohm when it gets to the home switch. Loose connections would make ohms higher than expected - so control isn't "seeing" home. 

I am not going to be at the machine for a few more days, but that is my best guess. I always assumed the home switch cuts the power to the motor, but that would actually cut the DC circuit. 

Only been working with vending machines since last year. Understanding control board signal processing is not in my skill set. 

[AZVendor]

The switch wire is a signal to the logic board to remove power from the motor.

[cvending]

Check to see if you have a price set for those seletioons.  If they lose their pricing, selections will not vend.

[divot]

I will check that. Though , the issue is not that they are not vending. 

Whenever any selection is purchased or tested in the last 3 shelves- the coil rotates like 2 or 3 times until the control board beeps 3 times and the customer receives 3 items. ( older machine without drop sensors - only home switches). 

Edited October 31, 2023 by divot

[divot]

23 hours ago, AZVendor said:

The switch wire is a signal to the logic board to remove power from the motor.

Right- so do you agree it is probably looking for specific ohm/ resistance and not a total open?

[AZVendor]

I think you either have a wire grounded out or a bad logic board.

[Vendo Mike]

Based on the wiring diagram, it looks like more of a matrix than 1 common to each motor and each motor having it's own supply. Unless multiple shelf wires are cut,  this would lead me to component failure on the board.

[divot]

So, it is possible for just some of the motor inputs on the board to go bad, without them all going bad? 

I was also thinking board, but was unsure of it could happen that way. 

Luckily I have a few written machines with this same  board

 

[Vendo Mike]

It's certainly possible. 

[AZVendor]

Swap boards between machines and find out.  That's how you can troubleshoot this problem.

[vwgo]

I think I can help but first it would help if you told us the model of machine your working on.  USI has made a few different machines.  But if it is a 3155 as in the pic of the schematic then there are a few things to check.  

You can do a motor check through the board.  Count all the motors in the machine then do the motor count on the board.  If they match then the board is seeing everything correctly and it all should be working.  If the numbers are off like you have 50 motors and the board only sees 35 then more than likely a bad wire will kill multiple motors.  Look at the plug where the shelf plugs in.  The wires will crack and break off at the plug from the shelf being pulled in and out for years.   Now if you get a really weird number like 97 then you either have a bad motor or bare wires between motors are touching each other.  I think this is your issue as it will cause motors to run more times or move multiple motors at the same time.  A mouse can get in a chew the wires and when the wires touch you can have these issues.  Normally though there would be signs of mice like eaten food or mouse poop.  If no signs of mice then the bad motor may be the issue.  Sometimes when a motor goes bad it can back feed current and give running on issues.  Also wiring a motor backwards can do this as well.  To find your bad motor first unplug all your shelves but 1.  Then do a motor check.  If you get the correct number then plug in the next shelf and do a motor check.  You will soon get to a shelf that will throw a bad number and then you know what shelf is the problem.  Then unplug each motor on the bad shelf till you start getting the correct number of motors to find the bad one. 

If you are getting the correct number of motors and can't find any bad motors or wiring issues then yes the board could have gone bad.  I tell all my vendors that they should all be using surge protectors these days as there is about $2000 in electronics in the vending machines and sense 2020 all the prices have gone crazy. 

Hope this helps.      

[AZVendor]

So you're a USI distributor.  I hope you don't use the bait and switch selling technique of finding locations yourself and putting too many machines, or new machines, into them and then trying to find buyers for the locations while some random operator runs them for you.

[divot]

It was the board. Machine had been in storage and not powered on for a few years. 

Luckily Vendors Tech had one SM6 available. At first, their price seemed expensive until I realized I couldn't find these boards anywhere online. There was one option locally but that wouldn't be "refurbished" with a warranty. So, even at the price I paid- I'm glad Vendors Tech had one available. 

Would have made more sense to troubleshoot with one of the boards from my other SM6 machines, but they are all in good locations. I didn't want to disrupt them unnecessarily and I also figured if I bought the board from Vendors Tech- the 3155 shouldn't have any control board issues for a minute and I would have a much needed spare SM6 ( once I have it fixed). 

Thanks for the help