Hello,
So I'm designing a circuit based on
this schematic, attempting a SNES/NES dual-purpose controller, basically. I have everything wired up correcty on my breadboard (after quadruple-checking, trust me!), and yet after every troubleshoot, the same thing keeps happening.
The test cart: SMB World. The intro, within seconds, goes to the game select screen on its own; sometimes it selects a game and then selects 1 or 2 player, sometimes it goes to player select and then back, sometimes the selection cursor moves on its own. Obviously buttons are firing on their own. There is a very brief time window in which I can give an input command on my own, and the correct buttons do the correct things.
Map screen: I'll explain what happens in 2-player mode, as more buttons are utilized in the map. The map screen won't be on for one second after fade-in before a button command fires on its own. Sometimes it's B to start the level I'm on; sometimes it's Select to bring up the player switch menu; sometimes it's Down; and sometimes it's Start to bring up the map view mode. Inputting any direction will simultaneously fire Start.
Gameplay: This is where all hell really breaks loose. More often than not, the level will begin with Mario/Weegee crouched down. He'll remain crouched for about 5 seconds, and no buttons or directional inputs will work during this time. Atter that, there will be a very brief time window (1-5 seconds? it varies) in which I can input button commands, and they all seem to work, from what I can tell after numerous test cycles. Then what happens is what I can only presume is several/all buttons firing at once, usually Start and Select firing first in a split-second "one-two" manner, which pauses and immediately exits the level; this will happen on its own, even if I press no buttons. The process then repeats over and over from the map screen.
I tested all leads, the ICs and even the breadboard rows, and even tried swapping in new ICs. I've tried swapping the yellow (CLK) and red (DATA) wires, thinking maybe the colors were switched. I've tried disconnecting leads, one by one--even the +5V rail, and the only thing that seems to have an effect is disconnecting DATA (which results in no input commands fired and no response from any buttons) and disconnecting pin 8 of the first IC (the top one in the schematic) from GND (B still works, and pressing any of the directions will fire other simultaneous commands, but no other button seemed to work). I also tried removing the resistor networks. None of these methods seemed to identify a clear problem nor get me any closer to a solution.
What would cause this behavior? The common pattern seems to be [Down for 5 seconds with input disabled...input enabled for a very brief moment...multiple buttons firing at once, starting with Start and Select...repeat].
P.S.: For some of you reading this right now: yes, this means exactly what you think it means.
