• Published on | Feb 16, 2007 | by Chris Osborn

Wow this holds a lot of cans!

Last night when I got home the first thing I did was tinker with the Pepsi machine some more. I got out the flashlight and searched all over looking for the thermostat control (still haven't found it). While searching I found the rod linkage that goes onto the narrow slot. Didn't find any cams, although I'm considering trying to fabricate them. I have a drawing on the inside of the door that shows what it looks like.

I'm not sure how old the machine is, but it's largely an electro-mechanical contraption. The only electronics in it are the coin mech/coin changer. Because it's EM and has a lot of switches, I had been thinking that the large slots hadn't been able to reset because of the two missing cams and their switches not being able to close properly. The theory I had was that the open switches would lock out the rest of the motors.

Looking closer at how the mechanics worked I realized that it was designed so that only one of the two side bars could ever be up at a time so that wasn't why the cans were falling out. I carefully balanced a can on the bar that was up and it stayed, so I put another above and staggered to the other side, and it stayed too! The slot is also deep enough to hold two cans end-to-end, but I still wasn't sure if that was correct or not. There's another rocker bar in the middle, but it didn't appear like it would block a back can. I went ahead and loaded it up though and stacked them high enough to push the sold-out lever, closed the door and inserted a quarter. It promptly rejected my quarter even though the sold-out light for that selection was off.

Here's a crude drawing of how the cans are loaded, in case like me, you just got a machine and you're puzzled by how to stack them.

Not knowing how long it would be before I came up with another idea (and concerned that the cans might freeze and burst) I took the cans back out and went back to examining the schematics. After going over the schematics some more and tracing the wiring (and again looking for the thermostat), I found the credit relay was missing. A quick perusal of the web and eBay showed that it was a fairly standard relay module, so I pulled out the 12V relay I had in my MAME cabinet to see what the pinouts were. Comparing the numbering on the bottom of the relay to the numbering on the schematic I quickly figured out how to jumper the plug to bypass the need for the relay temporarily. I held down the sold-out lever, pushed the button on the front of the machine, and instantly the motor came to life!

Watching the mechanism turn and flip the bars back and forth was quite fascinating. It still didn't look like the rocker bar in the center would block a back stack of cans, but the only way to find out was to try it. I grabbed an empty can since I was going to be doing this test with the door wide open and didn't want full cans of soda smashing into the ground. I stacked the can on the bar, held the sold-out lever, pushed the button and out dropped the can! Neat! But this time after the can dropped the mechanism kept spinning. Uh-oh. Releasing the sold-out lever stopped it, but as soon as I pressed it again the motor started up again. I kept checking the cam, looked around for other switches that might be checking to make sure a can dropped, and then realized the button on the front of the machine had become stuck. I popped it back out and all was back to normal. I then tried the empty can in the back part of the stack and sure enough, it fell down and stayed in place, and then the rocker bar swung a little further on the next button press and the can came down.

Now I understand what they mean by the slot has to be primed when it was empty. It's sort of a 4 state machine, although it really can be left in only 2 states: "front can just dropped" and "back can just dropped." If it's in the "front can just dropped" state then the next time it goes to drop a can it will think there's a can back there and will drop nothing. After a load of a completely empty stack it's a good idea to cycle it once to make sure the cans are where it thinks they are.

When I discovered the missing relay I was thinking that I would see if the electronics store had a replacement. But now that I know how it works I think I will leave it off and leave a jumper in place so that the machine will always be on "free play." Much better than having to set the price to a nickel or something and leave a tray of coins on top of the machine.

Now if I could just get the machine in the house!

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