Source for 8-bit static shift registers for NES controller - Page 1
Forum section: electronics / repair

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: December 11, 2019, 12:58:19 am
content: I'm looking to repair a few NES controllers (and eventually make my own 3rd party controllers), and I need near identical pin-for-pin replacements for the CD4021BC IC to do it (corrosion seeped up the leads of the IC and got into the chip and damaged it permanently). As far as I know, these chips are obsolete. Does anyone know where I (and any other person looking to repair NES controllers) can find replacements, or worst-case scenario, alternative/different part number replacements?Also, I do have SIL4021BE ICs which essentially do the same thing, but they have CMOS protection on the inputs unlike the CD4021BC. Would this chip work in place of the original, or would it not function properly due to that slight difference? (I'm a bit afraid of trying it in fear that I'll kill something in my NES due to swapped pin(s) I might not have seen).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 11, 2019, 01:35:40 am
content: CD4021BE is readily available. I don't think they're using them in any odd way, standard types should suffice.Tim

author: fzabkar
author_rank: Super Contributor
timestamp: December 11, 2019, 01:45:46 am
content: Early CMOS logic was prone to latch-up failure if the input voltage exceeded either supply rail. I suspect that the SIL4021BE may have latch-up protection in the form of two diodes. I think you should be safe.Alternatively, there is always NTE (search for "4021B"):https://www.nteinc.com/specs/4000to4099/pdf/nte4021B_BT.pdfhttps://www.nteinc.com/search.php

author: edavid
author_rank: Super Contributor
timestamp: December 11, 2019, 01:49:32 am
content: As mentioned, CD4021BE is still in production, you just had the part number wrong:https://www.findchips.com/search/cd4021beYou can also use MC14021BCP, which is exactly the same part - it's no longer in production, but still readily available. (Maybe you got the two part numbers confused?)Also, why do you think a SIL4021BE is any different from any other 4021? I find that highly unlikely.

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: December 11, 2019, 02:07:13 am
content: Quote from: edavid on December 11, 2019, 01:49:32 amQuote from: fzabkar on December 11, 2019, 01:45:46 amQuote from: T3sl4co1l on December 11, 2019, 01:35:40 amOh, that's a relief. And yeah, maybe the part number is obscured or scratched up a bit, or maybe even modified by Nintendo for some reason (as they have done that before - modifying chip numbers to meet their service parts stock numbering / listing system).I guess the reason I'm a bit skeptical about using alternatives is because with logic chips, one wrong digit on a part number could accidentally identify a totally different chip function.I'll try the SIL4021BE. I'll also order up those parts you guys mentioned via the links. Thanks!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 11, 2019, 04:03:46 am
content: FWIW, my controller has a Matsushita (Panasonic) MN4021B. Who knows what age, but probably contemporary (80s).A bit amusing they didn't even put in a supply bypass capacitor, let alone anything else ESD or EMC related, but the choice of CD4000 (a fairly underpowered family, especially at 5V supply) is pretty deliberate, I would say.You certainly wouldn't want to substitute a 74HCxxx, but that wouldn't be pin-compatible anyway (hrm, would it?).Tim

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: December 11, 2019, 11:41:09 pm
content: Quote from: T3sl4co1l on December 11, 2019, 04:03:46 amThat's interesting. The controllers must have gone through several revisions that involved IC supplier changes. Possibly because NEC was expensive and high-quality, so they sacrificed quality for price and went with a cheaper IC.Quote from: T3sl4co1l on December 11, 2019, 04:03:46 amYou aren't wrong there. My controller has two unused, naked pads between VCC and GND where an (electrolytic?) capacitor would be placed. I think that they DID add in a capacitor during the first few revisions, but removed it in later revisions to conserve budget. If I added my own capacitor, I wonder if that would make any difference...EXPERIMENT TIME!!Quote from: T3sl4co1l on December 11, 2019, 04:03:46 amI mean, if I decided for whatever reason to use one of those series chips in my own controller design, I wouldn't mind rerouting a few traces. But I think that for the sake of keeping it original, I'll just go with a similar part with identical pin layout. I tested the controller experimental prototype board I built at school using an OEM IC from one of my working NES controllers, then with the SIL4021BE I had laying around, and it worked exactly the same. (I replaced where the IC would go with an IC socket so I can swap out ICs and test various chips' functionalities, thus why I called it an "experimental" prototype board. I'm using it to find what chips will work in my own controller designs. It's actually a pretty nifty board, I'll send a pic of it when I can if you are interested).Also, I just opened up my Genesis controller, it actually uses a 74HC157N. So the irony is incredible hereThough, that is curious... It looks to be a quad 2-input multiplexer. I wonder why they would use a multiplexer in this controller... Unless... They're using it to switch the data between a corresponding wire when a certain button is pressed. Why couldn't they just use transistors or just have done like the Atari and straight up used the buttons to short the voltage to the output?