I would then bang the machine around and see if you can introduce a fault as suspected when your pulling the door handle.

U2 and U83 are the same chip.  U3 and U70 are also the same chip.  Doing the initial ram clear is the easy part.  The machine settings are a lot more complicated.  The clear/set chips should have a designation on them that tells which iteration they are.  An example would be 6.03.04

What I do is open the door, turn on the power switch, press the little white Test button until I see a [10-0] in the Winner Paid window.
At that point, turn the Jkpt/Reset key three times to change that to [13-0] and close the door.
The zero will flash rapidly back and forth between a zero and a 1 if the door optics are aligned.

This has been showing for quite a while.  I'm attaching some pictures of the boards in the upper box.
The first two pictures are the boards that I took to Dallas and they checked them out and said they were good.  The last picture I did not take this board.  Is this the power supply?

Top photo is your Dotmation screen.  They're rugged but fragile.  If taken care of nicely, they tend to last quite a while and slowly degrade over time with burn-in and out gassing.  There are no replacements for them.  You may see 192x64 led reproductions for certain pinball machines that used the same style and size screen but they are not compatible. 

Second photo is the controller for the screen.  Strong board, never seen one fail to date.

Hi, All:

While I was trying to get more info about the "Bally 831" hopper on ebay, ie, measurements and photos from the seller, the thing sold, so I have lost that option.  I've been burned making hasty decisions to buy stuff on ebay, and this time my caution may have caused me to miss exactly what I needed.   I'll keep trying the vendors posted on the home page, but, so far, most of the responses I get amount to "good luck".

Something that I don't have yet is an actual part number of the hopper mechanism to search for.  Since my machine is very rare, it would be better to search for the hopper part number.  Can anyone be of any assistance in that regard?  I think we have established that my machine is likely model 1072, but I gather that hoppers from several machines will work if I change the payout disk.  (Which I gather is also a very uncommon type).  I think I can make one from a good drawing if it comes to that.

Meanwhile, I'm going to move the machine to storage, as it is badly in the way on my workbench.

Best

Mike