Atari Stunt Cycle video problem

jcjcjcjc131313

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I've been working on this Stunt Cycle board for a while and I'm down to the last issue, but I'm stumped. Hoping someone here has an idea based on the attached screenshots. As the cycle leaves the 2nd roadway off the left of the screen, a black area moves up from the road, goes back to looking normal, and then another black area moves up from the 3rd road as the cycle comes back onto the screen. This shouldn't be too hard to track down, but I've hit a wall. Any help is appreciated!

Thanks!
 

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I have this machine but haven't needed to do any board fixes. Last posts I saw around here about repairs were from @GothGirl and @Brick Top (possibly about the same machine?)

What I'm understanding from the pics is that each time the motorcycle is on a level but not being displayed the black line occurs. Maybe not on the top row?. The motorcycle graphic ROMs are OK, you can see the correct image when its called, but when they're not being called this other 'image' is being generated in possible horizontal locations for the cycle.

My guess is the horizontal window circuit, when not being fed the correct image parts from the roms, is feeding garbage into the shift registers which then display it at all possible positions. Id look at section 3.4.5 (page 9) in the manual detailing how the data is selected from the ROMs and check those chips. Id start by testing A4 (7474) and B4 (74107) which appear to send the pulses which choose the image parts from ROM. Wild ass guess but if there's a flip-flop involved anywhere Id test it first.

@lilypad19 might have a better guess?
 
VWINDOW looks ok... prob an issue with C4 / E4 / A4 on down the line to MS1/MS2

B4 should be fine since the line counters are getting reset at the right times, and the issue is prob only when H8/H9/H10 are high.
 
Spent a few more hours on this trying to chase it down, but still no luck. Otherwise the game plays fine. I did notice that in a two player game, player 1 gets the black area coming up from the road like in the pictures, but player 2 (with the black cycle) gets the opposite - a white blur that moves up in exactly the same way. Still haven't give up yet though!
 
Spent a few more hours on this trying to chase it down, but still no luck. Otherwise the game plays fine. I did notice that in a two player game, player 1 gets the black area coming up from the road like in the pictures, but player 2 (with the black cycle) gets the opposite - a white blur that moves up in exactly the same way. Still haven't give up yet though!

That confirms that the generation of CYCLE and /CYCLE is the problem... which goes back to everything I said before.
 
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