Sega Repair Viper Night Drivin' (Sega, 1998) Slam Tilt issue

Larrik

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Hi, first post here. I'm pretty new to pinballs, just having got my first 3 last month (along with some other vintage arcade machines).

I'm working on repairing two of them, but I'll stick to one for now:

I have Sega's Viper Night Drivin' game. It generally works fine, with a few weird behaviors at times. The most frustrating thing, though is that the ramp leading to the 3 "piston" bumpers in the back right field will often (but not always) trigger a slam tilt when the ball passes through it. I dismantled the actual slam tilt sensor on the coin door in a vain attempt to fix it. I don't see any other sensors in the machine nor in the manual.

I've read that sometimes wires can get crossed when they are on the same circuit, but the ramp and the slam tilt are no where near each other on the diagram (very different col/rows). I'm kind of at a loss on this one.
 
forgot to ping @pinballdaveh :)
Your info is correct about the switches being nowhere near each other in the switch matrix.
Have you tried going into self test switch test mode and watch the display of what switches show closed when you roll the ball thru the opto lane?
Possible problems
The opto may be clean but is going bad and might be sending the wrong info to the decoder chip on the cpu board.

Opto alignment is important and is explained in the manual.

Opto devices need 5 volts to work. If the voltage at the opto is too low a problem might happen.

Problem on the cpu board, bad component Or corrupted game rom.
 
Thank you!

I did not try the self test switch mode, no. Thanks for the list of causes. Google has not been friendly here.

I'll check it out soon and see what I can dig into (I have to move the machine into an area with a higher ceiling to really work on it, so it's a bit of a time investment).
 
Checking in here, I haven't fixed it yet, but a few of those steps were a bit beyond me. In switch test mode I didn't see anything surprising, and the opto voltages looked good. I tried re-seating the opto anyway. I couldn't trigger the slam tilt after the fact with my hand or throwing the ball at it, but when I closed it up and tried it for real it came back.

Right now the opto is just unplugged for a bit.

Giving some credence to it being a ROM issue, the machine does occasionally fire off extra balls. I assumed at first it was because I'm using the original glo-balls which are in rough shape, but in one game it just fired off 2 extra balls with a few seconds in between for no apparent reason.
 
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