NES - Player 1 controller not working. (NES PCB ISSUE)

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calima
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by calima »

Also, extension cables are cheap, for destructive purposes.
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Ben Boldt
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Ben Boldt »

So where do we go from here? You thoroughly proved that it must be a problem somewhere on the motherboard. Have you checked continuity of all controller #1 traces from the connector pins to the chip’s pins where it connects?
Drag
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Drag »

Other than continuity, you'd need an oscilloscope to check to see that the correct signals are actually reaching the controller port. I still suspect /INP 0 might not be right. Shorting it to ground made the console freeze because it activated the buffer, which would've interfered with the CPU trying to access ROM/RAM.
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by unregistered »

Fiskbit & calima,

Great ideas! :D

I was just thinking of all the used nes controllers purchased from GameStop… some of them don’t work and are kept just bc I paid a little money for them… I stated, “you could…” bc that’s something I’d do. (Yes, NES controllers are simple to fix; but, once fixed, they last me a looong time.) Obviously, it’s much simpler to cut the cord in half and strip the severed end; than to take out 6 screws, from the rectangular ntsc nes controller at least, test with the contacts and then replace the 6 screws.

AND, that destroyed useful cable can be stored and quickly used again.


Buying an extension cable is good, except for the buying-part taking searching, gas, time, and/or money. However, great ideas shared! 👍 :) Sry, was just explaining my purpose.
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Ben Boldt
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Ben Boldt »

Drag wrote: Sun May 22, 2022 9:58 am Other than continuity, you'd need an oscilloscope to check to see that the correct signals are actually reaching the controller port. I still suspect /INP 0 might not be right. Shorting it to ground made the console freeze because it activated the buffer, which would've interfered with the CPU trying to access ROM/RAM.
This really is a confusing issue to me. I have gone back and read more carefully. I find it strange that you have 2 of these NES that seem have the same problem raizenkohakus. Also, you seem to have more experience with this than most people. Are you repairing NESs a lot and over a period of time happen to have found 2 of them with the same problem? Or do you just have 2 NES and both broke in this same way? It seems coincidental that both break this way. Wondering if there is a common problem that breaks it. If so, maybe your new buffer chips broke too the same way? Just seems very unlikely that you have 2 of them with this problem.

I also see now where you did test a lot of the continuity. Hmm. What exact chip did you replace the 40H368 buffer with? Did you use 74HC368? 74LS368? Since the original part is CMOS (40xx, 74HCxx), it might work only marginal if you used TTL (74LSxx, 74Sxx). Also, sometimes these chips come damaged especially if they are old stock or pulls (AliExpress, eBay, etc.) Have you tried swapping the buffer chips and making sure problem doesn't move to controller #2? If it doesn't follow the buffer chip, I have to agree with Drag, it sounds like something wrong with /INP0, hopefully not broken CPU. But I do not know how you can break 2 CPUs like that, just very strange.
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Drag »

If /INP0 is indeed the fault, then it must be stuck HIGH, because we observed that the console froze when we shorted it to GND (forcing it low). If you can somehow see if /INP0 is toggling on the red wire, we could rule it out, but if it's stuck HIGH all the time, then that's the issue. If /INP0 is toggling the way it should, then it might be D0 (on the port side, not the CPU side) like maybe the capacitor is shorted to ground or something. I don't know how the capacitor would've gotten damaged though, unless PAL NES's are prone to damaging voltages being plugged into the controller ports or something.

And it's indeed strange that two NESes have the same fault.
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by unregistered »

Drag wrote: Sun May 22, 2022 5:49 pm I don't know how the capacitor would've gotten damaged though, unless PAL NES's are prone to damaging voltages being plugged into the controller ports or something.
Damaging voltage being plugged into a PAL NES’s controller port… like the voltage from a multimeter’s continuity test?

Hmmm… if that’s what you mean, then it’s good to understand that a multimeter sends DC voltage. At the same time, capacitors only respond to AC voltage. I’ve been taught that capacitors are often used in circuits to block DC voltage from reaching AC-only electronic parts.


That’s why measuring resistance on a guitar’s Tone potentiometer requires measuring underneath the capacitor soldered to the Tone pot. “Underneath” means placing the meter’s tips on the pot’s lugs; measuring using attached wires severely confuses the multimeter’s displayed values bc the Tone capacitor, in the middle, halts the DC current sent from the multimeter’s red cable tip.
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Ben Boldt
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Ben Boldt »

What you are saying is true for a capacitor in series. This is considered a high-pass filter, meaning that high frequencies can get through, and low frequencies (and DC) don’t get through. The higher the capacitance, more lower frequency is allowed through.

For capacitors in parallel, it’s different. Usually for every chip, there is a small 100nF capacitor in parallel with the power, I.e. +5V and GND. This capacitor actually stabilizes the power going to the chip. A small capacitor in parallel, like 100nF, is good for removing high frequency noise. (This may be called a “bypass cap”.) A large capacitor in parallel is good for removing low frequency ripple. (This may be called a “bulk cap”.) If this bypass capacitor you describe was to open up, the controller would still work, but you may get occasional glitches. If this capacitor shorted, since it is in parallel with the 5V and GND, it actually short out the entire NES and it won’t turn on. The capacitor or a circuit board trace may get hot and burn in this case since there isn’t a fuse in the NES. This is why I do not believe that the symptoms are telling us that there is a bad capacitor.
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raizenkohakus
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by raizenkohakus »

Ben Boldt wrote: Sun May 22, 2022 4:11 pm
Drag wrote: Sun May 22, 2022 9:58 am Other than continuity, you'd need an oscilloscope to check to see that the correct signals are actually reaching the controller port. I still suspect /INP 0 might not be right. Shorting it to ground made the console freeze because it activated the buffer, which would've interfered with the CPU trying to access ROM/RAM.
This really is a confusing issue to me. I have gone back and read more carefully. I find it strange that you have 2 of these NES that seem have the same problem raizenkohakus. Also, you seem to have more experience with this than most people. Are you repairing NESs a lot and over a period of time happen to have found 2 of them with the same problem? Or do you just have 2 NES and both broke in this same way? It seems coincidental that both break this way. Wondering if there is a common problem that breaks it. If so, maybe your new buffer chips broke too the same way? Just seems very unlikely that you have 2 of them with this problem.

I also see now where you did test a lot of the continuity. Hmm. What exact chip did you replace the 40H368 buffer with? Did you use 74HC368? 74LS368? Since the original part is CMOS (40xx, 74HCxx), it might work only marginal if you used TTL (74LSxx, 74Sxx). Also, sometimes these chips come damaged especially if they are old stock or pulls (AliExpress, eBay, etc.) Have you tried swapping the buffer chips and making sure problem doesn't move to controller #2? If it doesn't follow the buffer chip, I have to agree with Drag, it sounds like something wrong with /INP0, hopefully not broken CPU. But I do not know how you can break 2 CPUs like that, just very strange.
No, I bought a NES console from eBay which turned out to have the issue on Port 1, then I thought to myself to buy a motherboard to replace it, the motherboard I bought turned out to have the exactly same issue, then, trying to rule out circuits one by one on the motherboard I have started replacing what was easier: the buffer chips.

I have used SN74LS368AN TI (Photo attached) and I have changed botch Port 1 and Port 2 to verify whether the chips actually work. The new chip worked on Port 2 but Port 1 kept going with the same issue.


Would you recommend a specific game to test any "fluctuations" in button presses? Maybe I can reproduce the controller-in-and-out test using a game that could sense better, I am currently using "teenage mutant ninja turtles", I could possibly try "Robocop".


Pressing on the Pin 36 pin, reading the nesdev wiki I can understand:

2A03:
/OE1 PIN 36 goes active (zero) when A0-A15 pins = $4016,
Pin 34 CPU- R/W = 0, and Pin 31 - M2 (PHI2) = 1.


Could shift register demux chip U3B 74HC139 cause Port 1 to stop working?

L.E: I have ordered a cheap 20MHz Hantek 6022BE Oscilloscope to check signals. It may not work as U6 goes up to 22MHz but the 100MHz scopes were way out of my league.
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Ben Boldt
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Ben Boldt »

raizenkohakus wrote: Sun May 22, 2022 11:52 pm I have used SN74LS368AN TI
74LSxx series (i.e. TTL) has a lower V(IL) voltage, meaning that a logic low input has to be less than 0.8V, as opposed to the original CMOS chip, where logic low input only has to be lower than 1.3V. But since your original CMOS chip also had the same problem, this probably isn't the issue.
raizenkohakus wrote: Sun May 22, 2022 11:52 pm L.E: I have ordered a cheap 20MHz Hantek 6022BE Oscilloscope to check signals. It may not work as U6 goes up to 22MHz but the 100MHz scopes were way out of my league.
The NES has to bit-bang the controller, so you can expect that the toggles are a lot slower than the clock speed of the CPU. There will be several instructions per toggle, so it probably slow it down by ~10x or so, just guessing. You may not be able to see details like rise time and fall time of the signal, but it will provide very useful information. For example, if the signal is stuck always high, or not going low enough for V(IL), this will probably be easy to see.
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raizenkohakus
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by raizenkohakus »

1) I have had a play with the scope and I have tested pins 35 & 36 of U6 (all the way to the buffer pins) for /OE1 and /OE2) and can't say that I have found any differences, so this particular signal seems fine..

2) I have looked at the DATA pin on the green connector ports on the PCB. It seems that the controller is being detected on both ports ( i can see spikes being triggered)

3) Next step is probably to rule out the diode packs by buying new ones.
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Controller-insertion-data-pin.png
OE1-2.png
unregistered
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by unregistered »

@Ben Boldt,

Thank you so much! 😀 It’s interesting that a capacitor in parallel with power will adjust the power quality entering a chip! Really cool to know! :)


For those interested:

series == “daisy-chained” items

parallel == if you wanted two resistors in parallel, you’d just twist each side(of the resistors)’s pins together; then solder each set of twisted-pins into the circuit


(The math to determine resistance of resistors in series is different from that math used for resistors in parallel; so series and parallel use is a basic necessary construct for circuits.)


Sry raizenk, I’ll be quiet; have nothing to add.


FINAL-EDIT: Ben Boldt, you said when a capacitor is in parallel with +5V power and ground, the capacitor adjusts the power sent to a chip. Is the +5V a DC power? AC comes from the wall.

https://en.m.wikipedia.org/wiki/Alternating_current
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Ben Boldt
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Re: NES - Player 1 controller not working. (NES PCB ISSUE)

Post by Ben Boldt »

What can the problem be? The signal looks good like it should work.
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