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 Post subject: Controller false inputs
PostPosted: Tue May 15, 2018 11:57 pm 
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I have a few (3) controllers that are giving false inputs on the start button. Sometimes on its own an sometimes shortly after A or B is pressed (not sure if this is coincidence). All of them have the exact same issue. I tried opening the controllers, but I don't see anything obvious that could cause this. Any ideas on what the cause could be and if i should try to fix them or just get new ones?


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PostPosted: Wed May 16, 2018 12:50 am 
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Sounds a lot like the "APU DMC conflict glitch": https://wiki.nesdev.com/w/index.php/Sta ... ict_glitch

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PostPosted: Wed May 16, 2018 1:22 am 
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I would have guessed the same thing if this happened on all of my controllers. The 4th controller is fine and doesn't cause any issues. All the other controllers did this in games that don't even use DMC.

EDIT: Didn't the wiki page say that this is fixed on the PAL NES?


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PostPosted: Wed May 16, 2018 4:42 am 
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Yes, to the best of my knowledge, PAL units don't have this problem.

Some questions:
-So only 3 out of several other controllers have this problem?

-A and B gets interpreted as start. What about select? Considering that (a) select is not always utilized, and (b) it comes between A, B, and start when you decode the serial output of the controller:

Code:
BUTTON_A = %10000000
BUTTON_B = %01000000
BUTTON_SEL = %00100000
BUTTON_START = %00010000
BUTTON_UP = %00001000
BUTTON_DOWN = %00000100
BUTTON_LEFT = %00000010
BUTTON_RIGHT = %00000001

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PostPosted: Wed May 16, 2018 5:18 am 
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Seems like one of the wires is having bad contact.
It happened with me, one time it was a wire that was getting broken inside the cable, other was the cable connector that was rusty.
To be sure this is the cause of the problem is easy, just test the cable for continuity.


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PostPosted: Wed May 16, 2018 10:52 am 
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An important detail I forgot to add is that the false input on start doesn't happen immediately after A or B is pressed. It usually has a delay up to few seconds. Usually it is around half a second. Not sure if this changes the suspicion on what could be broken though.


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PostPosted: Wed May 16, 2018 11:22 am 
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I assume this happens across any number of games used? Do other buttons respond correctly? What happens if you push start to unpause and hold it? Sorry for all the questions, just looking for a lead/things to rule out.

Besides checking for continuity, you could monitor signals with probes an oscilloscope along with a simple test program on the nes. Maybe one that strobes and reads per second rather than all at every 60hz tick. Maybe that could help identify some lead.

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PostPosted: Wed May 16, 2018 10:28 pm 
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Now that I tested the controllers again they seemed to work correctly again. What I did yesterday was that I opened the controllers and washed the buttons and the rubber pads. This also seemed to fix issues in the controllers where you had to push the button harder than normal to get the correct input.


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