Atarians Flippers- Strange Pulsing

[Bill_Sacto]

Hi,

I hope someone can help me figure this out. I just picked up an Atari Atarians and it works fine except... when the flippers are energized and held energized- the solenoids start to pulse, on/off/on once per second for about a 1/4 second. I traced the circuit back through the drive transistor, through buffer, back to a 9334 Addressable Latch. The signal out of this latch, going back to the solenoid is a square wave, 60ish Hz @ around 10mv. I don't get this...

 

I don't understand what is causing the solenoids to pulse this way. It doesn't seem to me that it could be related to the signal I found at the 9334 (60 Hz). But I don't really understand that signal either.

 

Does anyone else have an Atari pinball? Do your flippers pulse?

 

Thanks for the help!

 

Bill

[Atariman]

That's peculiar... I've never seen that behavior on my other Atari pinball machines (although, they could be a little different - I, unfortunately, don't own an Atarians machine). The only issue I've got that sounds similar is with my Hercules machine - the flippers will occasionally stick in place for a short time after releasing the button.

 

Kind of a long shot, but have you tried replacing the solenoid? I wonder if it has something to do with the diode that is on it... Sorry for the potentially less-than-useful response - I haven't had a lot of time to troubleshoot my machines yet (hopefully I'll have more time this summer).

[Atariman]

Thought of one other thing - I wonder how feasible it would be that the solenoid is drawing too much current (for whatever reason) and is causing the solenoid driver to thermally shut down. Since I doubt they would've had anything built in to protect against this, I could see it causing the flipper to flutter like that as it oscillates between its working state (after it cools off a bit after shutting down) and its thermally shut down state... Just a thought.