SOLVED: It was the belt and/or the lower pulley and a loose connection..... somewhere.
I just opened the machine right up, and carefully inspected and seated each connection. Inside the cabinet, under the playfield, and inside the backboard. I gently pressed on every ribbon and wire connector and joiner on every board and gently pressed in each wire that looked like it may be loose. I didn't find anything that seemed like the obvious fault. I found one old repair with a sinlge heavier wire spliced onto the lighter original wire by finger twisting and electrical tape that was loose, and soldered into the UDC connector. The connector looked fine so I cut out the twisted together join and made a fresh wire join with a solder splice and reused the same wire and connector. I also reinsulated the heavier wire with a bit of heat shrink over a couple of tiny nicks in the insulation. I straightened anything that looked like it could be connecting with another circuit. I moved any wires that looked like they may be close enough to be sending any interference or noise to another circuit. When I closed it up and turned it on it all worked perfectly. The electrical interference on the dot matrix screen has completely gone and the display is perfect. The Caster's Club is working perfectly through all cycles. It is popping balls into the reel and ejecting them onto the playfield exactly as it should.
I'm kinda annoyed with myself because I read months ago that the problem was probably the drive belt on the reel. I even had a new spare belt and lower pulley in my repair box, but I hadn't changed them because they looked to be working fine. This time I could notice the belt was a little warped, so I spent half an hour and changed the belt and pulley and "Whoa! Looks like you got one on there Ace!"
Summary:
Multiple problems with the Caster's Club/Reel Assembly/multiball feature. Intermittent distortion/interference on dot matrix screen.
*Ball not registering (delayed timing) when seated in Caster's Club. Fast Cast registering: Yes. Ball ejected into rail to reel assembly: No (Would eventually pop up, sometimes after another ball was in play)
*Reel compartments not aligning with the rail from the Caster's Club. Sometimes causing multiple balls to stack in the rail and/or become lodged in the same reel compartment and cause the reel to jam under motor power with the second ball wedged between the first ball, the reel compartment, and the playfield rail.
*Reel constantly spinning when trying to eject/find balls from the reel compartment causing the balls to be stuck in the reel or eventually pop out (it should only move about 1/6 of a rotation to eject a ball).
*Balls being ejected erratically from the reel "Whooooooooooa!", immediately or randomly during game play even though there was only one ball (locked) in the assembly.
*Quantity of balls in play not registering during multiball causing extended play on ball after it should have ended.
*Multiball starting at random times during play.
*Reel test showing one opto constantly closed and one constantly open with multiple errors generating.
*On screen fault displayed after game play: Check switch 37, Check switch 38 (opto 1 and opto 2)
*Intermittent distortion/interference/signal noise on dot matrix screen. Visible on first test pattern (solid line moving left to right across screen) and page generation test as missing dots. Causing some screens to be completely unreadable, including the test/adjustments/set up screens, the in game score screens, and the Fish Finder screen. Distortion (like static) appearing across game screen in time with the topper fish flapping about.
Work previously conducted:
Replaced all optos (transmitters/receivers, white & black) - No noticeable effect/problem not resolved.
Solution:
*Checked positioning of optos and wiring against photos in this thread posted by Northerndude. They should be the same as pictured, with the black ones positioned under the reel assembly and the white ones on the outside of the reel assembly. Mine were correct.
*Cleaned the optos with a cotton tip and some Mr Sheen (furniture/multi surface cleaner and polish, also works great on the playfield). The optos looked clean and no significant grime appeared on the cotton tip (I do not think this was the problem).
*Replaced the drive belt and lower pulley on the reel assembly with new spares. (Disconnect the ball rail from the reel bracket & remove the back plate from the playfield surface. Loosen the top two mounting bolts on the light board (under the playfield) and move it aside to access the mounting bolts for the reel assembly. Disconnect the opto cable UDC connectors from the opto board. Disconnect the reel motor power supply connector from the power supply board. Remove the reel assembly mounting bolts and rotate the reel position until you can remove the entire assembly through the underside of the playfield (It should come through freely without being forced). Unbolt and remove the opto bracket. Loosen the locating grub screw on the lower pulley shaft and remove the nut, remove the retaining clip on the reel, and slide the reel, belt and pulley off the mounting shafts. Inspect the reel and upper pulley for damage (replace if damaged). Clean the reel and the mounting shafts with playfield cleaner (I use Mr Sheen). Inspect the motor wire connections and the UDC connectors. Fit new lower pulley. Fit new drive belt and fit reel onto mounting shaft. Refit the lock/nut and tighten grub screw on the lower pulley shaft and the retaining clip and washer on the upper reel shaft. Clean the optos and refit the opto bracket to the reel assmebly. Refit reel assembly to machine in the reverse order of removal. Reconnect the the opto and power supply boards.)
*Conduct detailed visual inspection of all wiring and connections and ensure all connectors are undamaged and firmly seated on boards with all wiring firmly fitted into connectors. Ensure there are no crushed diodes/capacitors etc and gently straighten any that may be folded over, no loose, damaged or unconnected wiring, no wiring connecting with board surfaces that could be creating electrical field interference.
Result:
*Caster's Club/Reel Assembly/Multiball feature running perfectly through entire sequence. All issues resolved.
*Dot matrix screen solid, crisp and clear on all screens. All issues resolved.
*Reel test is functioning with no errors and showing the opto switches opening and closing in sequence through the circuit test.
*The display test is clear on all screens and displays "RAM OK"
Conclusion:
*This issue was most likely caused by a worn/stretched/loose drive belt on the reel assembly and complicated by a loose connection or electrical field interference somewhere on the boards.
Recommendation:
* Replace the drive belt and lower pulley
* Clean the optos
* Check and correctly seat all wiring, connectors, and joiners.
I have just played about 30 games without a single issue. It's fixed!
[Full disclosure: To my great shame, this problem has been going on for years, not months, I've had it turned off all year and have spent years with the spring removed from from the Caster's Club gate to stop the gate dropping and playing without the multiball feature, because I just couldn't figure it out. If anyone would like more info on the above, I am more than happy to help out. I will probably only be on Pinside when I have a problem, so please also email me ([email protected]) and if I can answer a question, I will. In the meantime, if Madonna calls, tell her I've gone fishing and she should leave a message.]