This problem has got me totally thrown
When I picked up the game, I did the usual stuff when I get an untested special.
After fixing the monitor, testing the voltages and regulators, upon power up, the game boots into attract mode just fine.
The problem appears when you start a game. The paddle itself is positioned all the way to the right (in Test Mode the value reads as a 00), and no manipulation of the paddle potentiometer has any effect. I instantly thought to myself that it was the LM319 comparator, but the scope says otherwise.
The voltage ramp is working, and the pot itself is working to give the comparator output a nice square wave. When moving the paddle, the square wave does change.
Onto testing the 74LS132, I checked that SENSE1 is working right, and I get a clean pulsing signal, that again changes when the pot is turned.
I followed the signal to /NMI where the CPU gets the signal just fine.
But still, the paddle itself doesn't move. The only thing I find odd is that the SENSE1 example in the manual doesn't exactly fully match what I see on my scope.
The example shows that with the pot input at +5v, high should only pulse for a very small amount of time, but when I max out my pot to get the same effect, it's high for a slightly longer duration. Lowering the pot voltage increases the duration of the high pulse, but I cannot get it to pulse high for that small amount of time shown in the manual.
I'm wondering if I'm out of range for the pot to be read. I don't know what would cause that, or if I'm totally off base with that idea. Has anyone had any experience working on this kind of issue?
Seems like a simple enough circuit, but it's got me.
When I picked up the game, I did the usual stuff when I get an untested special.
After fixing the monitor, testing the voltages and regulators, upon power up, the game boots into attract mode just fine.
The problem appears when you start a game. The paddle itself is positioned all the way to the right (in Test Mode the value reads as a 00), and no manipulation of the paddle potentiometer has any effect. I instantly thought to myself that it was the LM319 comparator, but the scope says otherwise.
The voltage ramp is working, and the pot itself is working to give the comparator output a nice square wave. When moving the paddle, the square wave does change.
Onto testing the 74LS132, I checked that SENSE1 is working right, and I get a clean pulsing signal, that again changes when the pot is turned.
I followed the signal to /NMI where the CPU gets the signal just fine.
But still, the paddle itself doesn't move. The only thing I find odd is that the SENSE1 example in the manual doesn't exactly fully match what I see on my scope.
The example shows that with the pot input at +5v, high should only pulse for a very small amount of time, but when I max out my pot to get the same effect, it's high for a slightly longer duration. Lowering the pot voltage increases the duration of the high pulse, but I cannot get it to pulse high for that small amount of time shown in the manual.
I'm wondering if I'm out of range for the pot to be read. I don't know what would cause that, or if I'm totally off base with that idea. Has anyone had any experience working on this kind of issue?
Seems like a simple enough circuit, but it's got me.

