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PostPosted: Tue Jun 06, 2017 6:45 pm 
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I have two problem NES controllers, both 004s. One controller does not respond when the dpad is pressed left, and the other controller is completely "dead".

Both appear to have intact traces, so I'm wondering if maybe the IC is at fault in both controllers.

The chip is a HEF4021BP, which i beleive the important numbers are 4021, making it an 8-bit static shift register.

Would any 4021 chip be a drop in replacement? If I simply desolder the old chip and put in a new one, even if the exact naming doesnt match, would it still work? I'm thinking of buying a small lot and trying this. Please let me know what I should be shopping for.


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PostPosted: Tue Jun 06, 2017 7:05 pm 
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Yup. 4021s are a standard part.

( see also )

I've actually also got a NES controller with a dead 4021, which I've desoldered, and haven't gotten around to buying a replacement.


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PostPosted: Tue Jun 06, 2017 8:17 pm 
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Great. So then I could buy any IC that contains "4021" and has the correct number of pins? It doesn't matter what comes before or after the 4021 on the IC label?



Secondary question.....what would cause only one of the inputs to fail? The one controller works with nearly every input. A, B, Start, Select, Up, Down, and Right. Only Left on the dpad is dead. What might have caused that? There's no physical damage to the IC, no rusting, no damaged traces. I don't get it.


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PostPosted: Tue Jun 06, 2017 9:05 pm 
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After 30 years? Who knows... 4000 series parts are somewhat static sensitive, but are relatively quite tolerant of "ordinary" overvoltage (up to 15V), and this one is inside the plastic controller. I don't know how any static buildup would have been induced.

Last time I wrote:
read HCF4020BE as:
  • HCF = manufactured by ST microelectronics
  • 4020 = 14 bit ripple-carry counter
  • B = buffered inputs
  • E = DIP
Each manufacturer uses different suffixes; e.g. some use "N" to mean DIP. The numbers are standardized.

Semiconductors often fail at a scale that's too small to see (as well as covered in epoxy). It's possible that if you decapped the 4021 and looked at it with a microscope, you'd see what went wrong ... maybe. Or maybe you'd actually have to remove the layer of metal at the top and maybe dye the die.


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PostPosted: Tue Jun 06, 2017 9:41 pm 
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Hmm...makes me think that the other NES controllers I have are a ticking time bomb. Good thing 4021s are cheap and easy to find and the replacement process isn't overly difficult. Thanks for the help!


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