AV Famicom exhibiting ghost inputs

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geraldtjy
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AV Famicom exhibiting ghost inputs

Post by geraldtjy » Tue Sep 08, 2020 2:50 am

Another issue, this time with an AV Famicom, which I hope you all don't mind me asking 😅.

I had been using an AV Famicom for some time, then left it unused for some time, and now when I hook it up it seems like it think the controller is pressing various buttons (a lot of times it's pressing up).

I tested with various controllers and it's the same issue. This did not happen in the past. I tried to just clean the board with IPA and contact cleaner but the issue still occurred.

The NES accepts input from a the controller port in serial, so I don't think any specific pin is shorted.

Any ideas is very much appreciated. 🙏🏻
avfamicominputs.mp4
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lidnariq
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Re: AV Famicom exhibiting ghost inputs

Post by lidnariq » Tue Sep 08, 2020 1:49 pm

Since you already have a flash cart, could you record what happens if you use either rainwarrior's or my joypad test programs?

nocash
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Re: AV Famicom exhibiting ghost inputs

Post by nocash » Tue Sep 08, 2020 4:36 pm

That happens only if the controller is connected, and without pressing any buttons?
Normally the controller should output 8 high bits in that case (same as when no joypad connected at all) (however, with the controller connected, you'll get low bits after the 8th bit).
One guess: The joypad doesn't receive any power.
Other guess: The shift CLK pin outputs noise, causing the controller to shift-out the data too fast.
Don't know why it ends up pressing up. Might be random timing. Or the game cart preferes Up when pressing multiple buttons. The test programs might help there.
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geraldtjy
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Re: AV Famicom exhibiting ghost inputs

Post by geraldtjy » Thu Sep 10, 2020 9:43 am

Thanks for the responses. I'll try the test programs on my flash cart over the weekend.

And yes, it happens only when the controller is connected, and without having to press any buttons.

The joypad still 'works' (i.e. you can still use the dpad and buttons, but it will also exhibit other random inputs that were not pressed)

Considering it's a serial input my assumption was there's some timing issue with the controller input. Not sure how I would resolve that. I would try to post the out come of the tests over the weekend.

geraldtjy
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Re: AV Famicom exhibiting ghost inputs

Post by geraldtjy » Sat Sep 12, 2020 9:32 am

lidnariq wrote:
Tue Sep 08, 2020 1:49 pm
Since you already have a flash cart, could you record what happens if you use either rainwarrior's or my joypad test programs?
Found some time to give it a shot. I've attached the videos of the program - you can see that there's no issue when there's no controller, and when the controller is plugged in it's displaying random inputs. I've tried with various controllers and have the same issue.

Still at a loss as to what I can do about this 😅
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controller_random.mov
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no_controller.MOV
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lidnariq
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Re: AV Famicom exhibiting ghost inputs

Post by lidnariq » Sat Sep 12, 2020 10:36 am

Maybe the contacts inside the controller jack are making a bad connection?
If you try running my test program with the controller in the other jack, does it produce the same blinky dots but six rows lower?

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Jeroen
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Re: AV Famicom exhibiting ghost inputs

Post by Jeroen » Sat Sep 12, 2020 10:54 am

This is just a quick theory as I don't have a lot of time to dive into it:

https://console5.com/techwiki/images/7/ ... -Ports.png

This is the nes controller port schematic, if some of the diodes DA1, DA2 etc went short circuit, it could be that when the controller pulls down the data line, it also pulls down the data clock line etc. To test this you can remove the diodes and see what happens. (It's only for esd/overvoltage protection, so it won't hurt to test this way.)

geraldtjy
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Re: AV Famicom exhibiting ghost inputs

Post by geraldtjy » Sun Sep 13, 2020 10:12 am

Tested again with 2 controllers connected - Both controls seem to exhibit random inputs irregularly, although it seems to happen more frequently on the player 1 controller.

Thanks for the suggestion on the diodes. I might try that out when I can find the time. I still hope to get this solved since I still like the AV Famicom the best.

That said I will probably be looking to NESRGB mod a French NES first and see how that goes. 😬 Hoping the NESRGB will bypass the entire B&W issue I'm currently facing with it.
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Jeroen
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Re: AV Famicom exhibiting ghost inputs

Post by Jeroen » Sun Sep 13, 2020 12:26 pm

Just for the record, you're using a pal controller on an ntsc unit? (There's some compatibility issues with the reverse)

The fact that it's both controllers worries me, as they have little in common other than the CPU. Which would suggest a damaged CPU.

Do you have any measuring instruments like an oscilloscope?

edit: I did some more research and remember that the av famicom consolidated a few chips: https://i.imgur.com/czHVCzG.jpg
the "jI0" ic

So if anything broke, there's a good chance it's that chip.

lidnariq
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Re: AV Famicom exhibiting ghost inputs

Post by lidnariq » Sun Sep 13, 2020 12:50 pm

It really feels to me like it's a contact problem: that the metal contacts inside the jacks on the front are making a bad contact, and you're picking up electrical noise - hence why both controllers often flicker at the same time.

I don't suppose you have an expansion port controller (for the DA15 jack) also?

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