SNES / Super Famicom Repair Reference

The Super Nintendo (SNS-001) and its Japanese twin the Super Famicom (SHVC-001) are two of the most repairable 16-bit consoles you will meet, but they hide a trap the NES does not: the same model number covers wildly different boards, and which board is in front of you decides the diagnosis, the picture quality you can expect, and every mod choice. So this page starts with board triage, then works through the faults. It is written for someone comfortable opening the console and using a multimeter; where a step needs more, I say so.

One rule up front that saves the most time: identify the board before you theorize about the fault. A bright vertical line means one thing on a multi-chip board and is fixed a different way on a 1CHIP. A too-bright, ringing picture is a defect to chase on one board and stock behavior to leave alone on another.

Which board you have, and why it decides everything

The case tells you almost nothing beyond original (001) versus New-Style (101). The board is the real unit of identification, and it is silkscreened next to the cartridge slot. There are three families:

• Multi-chip, the community “2-chip” or “3-chip” boards. Separate S-CPU, S-PPU1 and S-PPU2 chips. Revisions SHVC-CPU-01 (the earliest Super Famicom, with a plug-on sound module), SNS-CPU-GPM-01 and -02, SNS-CPU-RGB-01 and -02, SNS-CPU-APU-01, and the PAL SNSP-CPU-01 and -02. These apply a baked-in horizontal blur to RGB that a clean buffer cannot undo.
• 1CHIP. Nintendo fused the CPU and both PPUs into a single S-CPUN ASIC in 1995. Silkscreen SNS-CPU-1CHIP-01, -02 or -03 (and the PAL SNSP-CPU-1CHIP variants). These carry a plain “SNS1CHIP” marking near the slot and output inherently sharp RGB.
• New-Style / Jr, board SNN-CPU-01, used in the SNS-101 and Super Famicom Jr. Same S-CPUN silicon as a 1CHIP in a small shell. Composite-only from the factory, but equals or beats 1CHIP picture once RGB is restored.

Telling them apart without full disassembly: the 101 is smaller and rounder, with a circular reset button and power slider and no eject button. On a PAL unit, pull the bottom expansion-port door; a 1CHIP shows a plain area behind it while a multi-chip board shows a dot pattern. On North American units, a serial beginning UN3 raises the odds of a 1CHIP but never proves it, because late multi-chip (APU-01) boards also turn up in those cases. The only definitive method is to read the silkscreen: remove the metal plate under the cart-release lever to expose the full revision string and the main chip.

There is also a set of in-game debug menus (Final Fantasy Mystic Quest, The Lion King, and a couple of others) that print the CPU and PPU die revisions, but Nintendo stopped incrementing those numbers once the boards consolidated, so they do not distinguish the late revisions. Read the silkscreen.

Why it matters for the picture: every S-CPUN board (all 1CHIP revisions and the Jr) outputs markedly sharper video than any multi-chip board. Within the multi-chip group SHVC-CPU-01 is the best by a hair and APU-01 is the worst. Within the 1CHIP family, do not use the sub-revision as a proxy for quality; the one review that tested many units found awful-looking -02s and phenomenal -03s, with the spread tracking component condition rather than revision.

A chart will lie to you about the U10 op-amp

One identification detail is worth a specific warning because the sources disagree. Starting somewhere in the multi-chip run, Nintendo replaced the discrete quad op-amp at reference designator U10 with its own integrated mixer, marked S-MIX. ConsoleMods says that swap began with SNS-CPU-APU-01; Console5’s per-board lists and the board photographs I have seen put S-MIX at U10 a revision or two earlier, on SNS-CPU-RGB-01. There is no chart that resolves it. Read the actual marking on the 14-pin chip at U10 on the board in front of you rather than infer it from the revision string. That is a good habit for this platform generally: the factory substituted parts, depopulated circuits, and omitted caps in ways that make any “this revision always has X” claim risky.

Common problems and fixes

Won’t load, freezes mid-game, or works only after reinsertion

This is the single most common fault, and it is almost always the cartridge interface rather than a chip. Start by cleaning the cartridge edge contacts with high-purity (99 percent) isopropyl alcohol and a lint-free swab, then retest two or three known-good carts. If several clean, known-good carts all misbehave the same way, the fault is the console-side 62-pin connector.

Here is where I part ways with the manufacturer. Nintendo’s own service literature is explicit that the 62-pin connector should not be cleaned, it should be replaced. I understand why they wrote that, but I do not follow it and I would not tell you to either. In my experience I have never met an SNES connector I could not clean back into reliable working order, and these connectors are not easy to source, with more than one physical type across the revisions to match on top of that. So I treat cleaning as the fix, not a stopgap: clean the console-side leaves the way you clean a cart edge, inspect them under a loupe for bent or spread contacts and gently re-tension any that need it, and reflow the connector’s solder joints on the underside, which is a common cold-joint spot. Replacement is my last resort, for a connector that is physically broken or too far gone to re-tension, not my first move. If you do replace one, note there is more than one physical 62-pin connector across SNES revisions; match the part to your board.

Dead: no light, no picture, no sound

Rule out the adapter before you open the case, and get the power spec right, because this is a console people kill with the wrong brick.

• NTSC (US SNS-001 and Japanese SHVC-001) takes 10 V DC, at least 850 mA, center-negative, unregulated. Meter an unknown brick before plugging it in: a center-positive supply is the wrong polarity here. (You will see 9 V quoted in some places; the OEM figure is 10 V DC and a 9 to 10 V DC center-negative supply is safe.) The North American jack has an inner pin specifically so a 9 V AC NES adapter cannot be inserted.
• PAL (SNSP) is different: it takes AC from the same brick as the PAL NES and rectifies it on the board, so the PAL jack tolerates either polarity. Do not feed a PAL unit a DC supply and expect it to behave like an NTSC one (more on that under the SCART hazard below).

With the adapter confirmed, the community’s reported order of no-power causes puts the DC power jack first: its plastic center post cracks with age and the joint fatigues, giving intermittent or dead power. It is a mechanical fault, and a common one. Reflow it first, and replace it if the post is loose or broken. For a replacement you have two good options: harvest a jack off a dead donor board, or buy a modern clone part for about 15 to 20 dollars. The clone is visually distinct from the original but a close match, and perfectly cromulent for getting the job done. Fair warning on the removal, though: getting the old jack off cleanly is genuinely hard without good equipment. It is a big, heat-sunk, through-hole part anchored into a ground plane, so plan on a powerful iron, a solid hot-air station, or both, and do not try it with a cheap pencil iron. This is also a job that is much easier to watch than to read, so find a good video of a SNES power-jack swap before you commit to your first one. The next suspect is the fuse, F1: 1.5 A, 125 V, fast-blow. It is a Pico axial part on the original consoles and a tiny SMD part marked F1 on the New-Style / Jr. Two things matter about it. Never fit a slow-blow substitute, because the fuse exists precisely to catch a wrong or overvoltage supply and a short to ground. And a blown fuse rarely fails on its own, so find the cause (wrong PSU, a shorted surge absorber, a downstream short) before you fit a new one and watch it pop again.

Nintendo’s own no-power priority list runs F1, then the series diode D1, then the T1 line filter, then the 7805 regulator (U12), then the VA1 surge absorber, then Q18, then the power switch (P3). The surge absorber (a small MOV) is the part nobody thinks of: a shorted VA1 pops the fuse instantly and repeatedly and looks like “the fuse keeps blowing.” Lift a leg to check it before you go hunting a downstream short.

Powers on but the screen is black or a solid color

This is the classic “it turns on but does nothing.” Work it in order:

1. Confirm the reset button is not physically stuck down, which by itself blanks the screen.
2. Boot a flashcart (an FXPak Pro or Everdrive). If the flashcart runs but a region-correct retail cart does not, the problem is the lockout chip, not the silicon (see region and lockout below).
3. If nothing runs, split CPU from PPU. The cleanest field test is a Super Game Boy with a known-good Game Boy game: no picture at all points at a dead CPU, while a working SGB border with a game that will not load points at the PPUs. A burn-in test ROM on a flashcart is better still, because it prints an explicit “CPU FAIL” line and exercises the RAM and PPUs directly.

On the underlying cause, the repair community is fairly unified, and I want to frame this as their reported experience rather than a guarantee: once the connector and solder joints are excluded, the black-screen SNES is reported to be “nearly always” a dead CPU, with the early S-CPU / CPU-A revisions the fragile ones and VRAM a distant second. I flag that as a strong community pattern to test against, not a diagnosis to skip the testing for.

There is one case people miss, and it is worth checking early on the right board. A dead audio subsystem can present as a black screen, not merely as silence, because the CPU waits on the sound system’s boot handshake, and Nintendo’s own fault table ranks a defective sound module second for a solid-color screen, above the CPU. On most SNES boards the sound chips are soldered down, but on the original Super Famicom board (SHVC-CPU-01) the whole sound section is a plug-on module, the SHVC-SOUND daughtercard, carrying the S-SMP, S-DSP, sound RAM, DAC, and amp. On one of those, check that module first: confirm it is present, fully seated, and making clean contact. A bad connection or a bad module will either keep the console from working at all or crash it the instant a game initializes sound. In my recollection a burn-in cart may run without the module until you enter its sound test, though I would not swear to that. This is the one board where reseating and cleaning a sound module is a real, cheap first move.

The rework itself (hot-air swapping a 100-pin QFP) is routine; sourcing a good donor chip is the hard part. A CPU/PPU test socket soldered to a known-good donor board lets you swap-test a suspect chip without desoldering it, and since the S-CPU and both PPUs share the same package, one socket covers all three. It is the highest-leverage bench purchase for diagnosing dead multi-chip boards at volume.

A bright vertical line down the center of the screen

Mostly a multi-chip fault, worst at power-on and in dark scenes (Super Metroid is the canonical test). It is a voltage sag on the 5 V rail during DRAM refresh, from insufficient bypass capacitance, and it is a console fault, not a cable fault. Confirm it strengthens in dark content, then fix it one of two ways: replace the stock 7805 with a higher-current linear regulator (an ST L78S05CV-DG, 2 A) and bump the small cap on its output to 22 uF, or add a 470 uF / 16 V electrolytic across the regulator with the negative stripe to the center pin (step up to 1000 uF if 470 uF is not enough). On a 1CHIP or any board carrying an RGB bypass amp, the bypass fixes the line on the RGB output; the regulator fix is the one that also cures composite and S-video.

Left audio channel louder than the right

A design defect on the early boards only, not aging. Nintendo tied both voltage- reference pins of the NEC uPD6376 audio DAC to a single shared 47 uF capacitor where the datasheet calls for a separate cap on each, and the resulting per-channel mismatch makes the left channel hotter. It affects SHVC-CPU-01, both GPM revisions, both PAL SNSP multi-chip revisions, and SNS-CPU-RGB-01. Later boards switched to the single-reference uPD6379A DAC, which makes the imbalance structurally impossible, so they are simply unaffected. The fix is to isolate one reference pin and give it its own 47 uF cap to ground. On the SHVC-SOUND module the relevant trace runs under the chip, so you lift a pin rather than cut a trace. If you ever replace a dead late-board DAC, mind the suffix: the 6379 and 6379A latch opposite channels, so the wrong part gives you swapped stereo that passes a mono bench test and comes back as a return.

Corrupt or scrambled graphics while the game keeps running

Distinct from a black screen. On a multi-chip board this points at the video RAM (the discrete SRAM at U4/U5) first, which is cheap and socketable, then the PPUs. Mode 7 titles (Super Mario Kart, F-Zero) expose early-stage PPU faults that ordinary games hide. Before opening the console, rule out the cartridge: Nintendo’s cart-side fault table lists a dirty edge connector, the program ROM, and the cart’s own enhancement chips as causes of “confused video,” so test a few known-good carts first.

A caution from my own bench on this symptom. A burn-in or diagnostic cartridge passing every test is weaker evidence than it feels like. I have had a console clear a full diagnostic cart, run most games correctly, and still corrupt graphics reliably on specific titles, and the fix was a CPU swap. Diagnostics exercise a subset of the machine; a game exercises whatever it happens to use. If a fault reproduces perfectly on the same titles every time, trust the repeatability over the diagnostic result.

Snow or analog video artifacts

A picture that is fundamentally there but crawling with snow, speckle, or other analog artifacts is worth separating from a dead or garbled screen, because the cause is often not the console at all. The first thing I do is swap in a known-good genuine cartridge. If the artifacts clear with a good cart, the console is fine and the cartridge is the problem.

The usual culprit is a cartridge with no bus interfacing at all, which the cheapest reproduction and flash cartridges skip entirely. Running lower-voltage memory against the SNES’s 5 V cartridge bus with nothing in between puts marginal signals on the bus and dumps switching noise into the rails the video circuitry shares, and that shows up in the picture as snow or artifacts. 1CHIP consoles in particular tend to be the least forgiving of marginal cartridge-bus signals.

This cost me a lot of bench time: I once suspected three SNES consoles in a row of bad video output before working out that the cartridge was the problem. I have since opened five flash cartridges and photographed what each one puts between the edge connector and the chips, including the one that caused this. See Flash Carts, Clones and Bootlegs: What Is Actually Inside Them.

1CHIP and Jr: too bright, ringing edges, and specific game glitches

These are inherent behavior of the S-CPUN, not faults, and chasing them as defects is a waste of a bench hour. All 1CHIP consoles output RGB that runs hot (too bright and washed out) and shows mild edge ringing. The community fixes are tuning, not repair: three 750 ohm resistors into the RGB via holes brings brightness to spec (1.2 kohm on the Jr), and a larger value for the on-board cap at C11 reduces the ringing.

The ringing fix has a trade-off that listings never mention, so I will: the S-CPUN’s DAC already responds poorly to rapid writes of the brightness register, which produces darkened top-of-screen scanlines and wrong fade effects in a known set of titles (several Capcom games, Air Strike Patrol’s missing plane shadow, Rudra’s warped text boxes). The larger C11 cap slows the DAC’s settling and makes that worse. So it is a taste-and-trade-off mod, not a strict upgrade. On original carts an FXPak’s firmware brightness patch mitigates the underlying glitch (with its own caveat: it can break games that DMA to that register, like Star Fox, so it ships off and is enabled per game).

No RGB sync on a CSYNC cable (1CHIP-03), and the PAL sync hazard

The SNS-CPU-1CHIP-03 revision ships with its composite-sync output circuit depopulated, so a CSYNC (pin 3) RGB cable gets no stable sync while a sync-on-luma cable works perfectly. That split is the -03 fingerprint. The easy answer is a sync-on-luma cable with no mod at all; the proper restore repopulates the missing sync components, and the cleanest path for a modded unit is an RGB bypass board that carries its own sync circuit.

Separately, and this one can cost you equipment: a PAL SNES puts 12 V on multi-out pin 3 for SCART autoswitching, where an NTSC unit puts a TTL sync signal. Connecting an NTSC CSYNC cable to a PAL SNES can damage your gear. Take sync from luma (pin 7) or composite (pin 9) on PAL. And if a PAL unit “stopped auto-switching the TV to 4:3,” suspect that someone ran it on a DC supply: the 12 V comes from a doubler that only reaches 12 V on the correct AC input, and sits around 7.5 V on DC, too low to trigger the switch. That is not a board fault.

Cosmetic: yellowed shells and hidden corrosion

The ABS shells yellow over time from UV and the bromine flame retardant in the plastic, and it is purely cosmetic. Retrobrighting brings the color back for resale. While the shielding is off, check under the RF can for corrosion that has not yet become an electrical fault; neutralize and clean it before it eats a trace.

I use the same corrosion process described in my restoration and testing writeup, then re-validate function separately.

Repairing a snapped-off edge connector

Reddit user Hungry4Italy posted a SHVC-BJ1M-20 board, a 1994 battery-backed save cart, with the whole gold-finger strip separated from the board across its full width. Not cracked, not lifting at one corner. Off, in one piece. Both photographs here are his, used with permission; the original thread is on r/snes and is worth reading for the replies as well.

He got it working again.

Not my greatest solder job, but after using 2 part epoxy and a clamp to repair the broken piece, I scratched the PCB to expose the copper and soldered the joint. Epoxy is extremely strong and it all works now.

Epoxy carries the load, solder carries the signal. Solder has no useful mechanical strength across a break that a cartridge slot works on every insertion, so the joint cannot do both jobs. Scratching back to bare copper on each side of the break is what turns thirty-odd interrupted traces into conductors again.

Cartridges from the first few generations are simple. The parts are large, most of them are through-hole, and the traces are wide enough to see and wide enough to put an iron on. Nothing on this board sits at a pitch that needs a microscope. People will tell you a repair like this is not economical, and they are usually right. With enough effort it can still be done.

One thing to get right if you copy it: keep the joints flat. A proud blob on a cart edge spreads or scores the console’s 62-pin leaves, and you find that out later, on other carts. He went back and reduced the ones he had built too high after another commenter raised it. Keep them at the top of the finger area, away from the leading edge, and test the repaired cart in the console you care least about.

It broke because the cart was knocked while it was inserted, and the crack grew from there over months before it finally let go.

I have not done this repair myself, so I cannot tell you how it holds up over a few hundred insertions or whether the epoxy minds a warm console. If your cart is a common one, a donor board and a ROM transplant is less work.

Region, 50/60 Hz, and SFC to SNES conversion

Region is two separate barriers that need different fixes, and confusing them wastes effort.

The first is cartridge shape. Japanese, PAL and Korean carts use the rounded shell; North American and Brazilian carts use the blocky one. All regions share the exact same cartridge connector and pinout. A US console physically blocks Japanese and PAL carts with two plastic tabs at the back of the slot, which you can cut out or replace with a tab-free insert (use the insert on anything with collector value).

The second is the lockout chip (CIC). All NTSC consoles (Japan, Korea, US, Brazil) use the same F411 family; all PAL consoles use F413. The consequence people miss: a Japanese cart in a US console is only blocked by the slot tabs, not by lockout, because both are NTSC F411. So playing imports on a US machine can be purely mechanical, with no CIC mod at all. A true region change (PAL to NTSC or the reverse) is where you defeat or replace the lockout. The modern answer is a drop-in region-free CIC board (SuperCIC and similar), most of which also add a switchless 50/60 Hz toggle. Keep a CIC-on mode available: some SA-1 titles (Super Mario RPG, Kirby Super Star) detect a disabled CIC and refuse to boot, so ship a switch, never a permanent disable.

A 50/60 Hz switch changes only the video timing, not the color encoding. A PAL board forced to 60 Hz can still show black-and-white on a color-fussy set, because you have not converted PAL color to NTSC color, only the refresh rate. The fix for that is a display that syncs both, not more soldering.

That shared NTSC lockout is also what makes the Super Famicom to SNES conversion worthwhile: drop a cheap, plentiful Japanese 1CHIP board into a US shell and it plays US carts natively with no CIC or 50/60 Hz mod, because the only thing that ever blocked those carts was the slot tabs in the shell. Four things actually bite: match the shell generation to the board (the earliest four-foot SHVC-CPU-01 cases do not interchange with the later two-foot cases), deal with the cart-slot tabs, ship the correct 10 V DC center-negative brick wound for local mains, and do not attempt this with a PAL board (its on-board AC rectifier and 12 V doubler make it a poor fit for a US shell and supply). If you sell a converted unit, disclose it: it is a genuine Nintendo board in a genuine Nintendo shell, but the case serial will not match the board revision inside, which is exactly the check a knowledgeable 1CHIP buyer runs.

Mods worth knowing

RGB is already good on a stock NTSC SNES, which is the platform’s happy surprise, so the mods here are about matching the output to a modern display and about recovering the sharpness the multi-chip boards throw away. I do not reproduce anyone’s install guide or schematic; this is an orientation with pointers to the real instructions.

• The governing fact: a multi-chip board’s blur cannot be undone by a neutral buffer or RGB bypass. It needs an active deblur or sharpener. A 1CHIP or Jr is already sharp and needs only cheap tuning. The most common overclaim in SNES listings is that an RGB bypass “fixes” 2-chip blur; it does not.
• Multi-chip sharpening. The low-cost open path is the Torapu / Buttersoft filter mod (a per-channel op-amp and RC network built from cheap parts), documented in amaiorano’s per-revision build guides. The open THS7376-based SNEdge is an active sharpener, fab-it-yourself under an open-hardware license (NTSC tested, PAL still experimental). The turnkey commercial option is Voultar’s Edge-Enhancer, the one board that also cleans composite and S-video.
• RGB bypass and cleanup for all revisions. borti4938’s open SNES RGB Bypass (THS7374) comes in base, CSYNC and CSYNC-plus-S-video variants; the licensing across borti’s boards is mixed, so check the repo before you build or sell. RetroSix’s CleanRGB fixes the DC offset at the console so a purely passive cable works.
• 1CHIP tuning: the 750 ohm brightness resistors and the C11 ghosting cap described above are the near-mandatory cheap wins on any 1CHIP RGB unit, with the C11 trade-off in mind.
• Dejitter is a scaler-specific fix, not a picture upgrade. It matters only if the buyer runs a simple line-doubler that mishandles the SNES’s shortened scanline, and it can cause composite or S-video flicker on some boards, so leave it off by default. marqs85’s and borti4938’s dejitter designs are the references.
• Digital audio (S/PDIF) taps the sound DSP for a bit-exact optical or coax output. Two limitations to disclose: Super Game Boy audio and MSU-1 soundtrack audio are generated outside the SNES sound chips, so neither appears on the digital output.

One mod to never do or ship: the old 2-chip “YPbPr” component mod. ConsoleMods keeps its guide only for historical reasons and warns it can damage the video encoder. Use an HD Retrovision transcoding cable if you want component out.

If you would rather buy an SNES with the RGB and region work already done, everything I restore is in the shop.

Recap and parts

The SNES is not a routine-recap console, and the mass-leak advisories that exist for a Game Gear have no SNES equivalent. Its electrolytics are small audio-coupling and decoupling caps, not switcher caps under ripple stress, so the community consensus (which I share here as the sensible default) is to recap on symptoms: muffled or weak audio, audible bias noise, bulging or leaking cans, or as belt-and-suspenders on a resale unit you already have open. The one genuinely age-sensitive area is the SHVC-SOUND module on the earliest Super Famicom, whose caps sit inside a shielded module you have to pry open.

Practical notes:

• Board-specific cap kits exist (Console5 sells them per revision, leaded or SMD), and the cap values and designators differ by board, so identify the revision first. Read the value off the can and the silkscreen before you desolder; the published cap maps are a single-origin reference, good but worth cross-checking against the physical part.
• There is a documented conflict over whether the big 1000 uF reservoir cap (C67 / C58 depending on board) is even populated on North American boards. One source says it is factory-omitted on US units; the NTSC schematic shows it present. Do not assume a missing bulk cap on a US board is a prior repair, and do not assume it is there either. Look at the pads. If they are empty, populating that cap is essentially the same intervention as the vertical-line “add a bulk cap” fix.
• Fuse F1 is 1.5 A, 125 V, fast-blow: a Littelfuse 251-series Pico axial on the original consoles, a Littelfuse 451-series Nano SMD on the New-Style / Jr. Never a slow-blow.
• The 7805 regulator (U12) runs hot by design, dropping 10 V to 5 V linearly, and the heat alone is not a fault. If you replace it, keep it linear. Switching drop-in modules run cool but can inject rolling lines into the picture, and this is not a 5 V-only console: the raw input rail also feeds the video and audio circuitry through a transistor follower, so do not follow the common “run the regulator from 7.5 V to reduce heat” advice here, and do not skip the regulator and feed 5 V straight in.
• A few Japanese discrete parts and the Nintendo-custom mechanical parts (the DC jack, the 62-pin connector) have no distributor part number. Order them from a retro-parts vendor or harvest a donor. On a fleet, the worst board is your parts stock.

Test every unit with an enhancement-chip cartridge (Star Fox for Super FX, Super Mario RPG for SA-1) before you list it. Those carts are the only ones that use the outer pin groups of the slot and the only ones that load the 5 V rail hard, so a board that is marginal on power or has dirty outer contacts will pass a Super Mario World smoke test and fail for the buyer.

The data behind all of this

Everything above is the reasoning; what follows is the raw reference material I work from at the bench, structured so you can actually use it. It is folded by default because there is a lot of it. Expand any row or card for the detail, and note the confidence tag on every line, because a fair amount of this platform’s published data comes from a single source.

Capacitor lists

Per-revision electrolytic maps. The board revision decides the designators as well as the values here (the whole board renumbers at SNS-CPU-RGB-01, and the Jr has a list of its own), so identify the board before you order a kit.

Replacement parts

The non-cap parts an SNES repair actually goes through, including the ones Nintendo’s own no-power tree ranks ahead of the obvious suspects.

Inside the controller

The SNES controller IC is not a jellybean part. Nintendo built the pad two ways, and the service manual documents both.

• Single-IC pads use one 56V520, a 14-bit parallel-in / serial-out shift register in a 20-pin package. Twelve of its parallel inputs go to the carbon contact pads; two are spare.
• Dual-IC pads use two 56W545 8-bit shift registers cascaded. IC-B’s serial output feeds IC-A’s D IN, and IC-A drives the console.

Both are Nintendo house parts. There is no logic-family substitute for either: a 4021 is 8-bit, and nothing common gives you fourteen stages in one package. So a dead shift register means a donor controller, not a parts order. That is the opposite of the NES, whose pad runs on an ordinary CD4021 you can still buy.

The dual-IC button map is the one that shows you the protocol directly. Data shifts toward Q8, so the highest-numbered input leaves first:

• IC-A, PI 1 through PI 8: Right, Left, Down, Up, Start, Select, Y, B
• IC-B, PI 5 through PI 8: R, L, X, A

Shift that out from PI 8 downward and you get B, Y, Select, Start, Up, Down, Left, Right, then A, X, L, R, which is exactly the twelve-bit order software expects.

Power: the pad has no regulator. VDD and VSS come straight from the console through the cable, so every logic level inside swings 0 to 5 V. A healthy console reads roughly 4.75 to 5.1 V at the pad; meaningfully lower points at the console’s regulator, not the controller. If you are interfacing one to a 3.3 V microcontroller, the data line coming back at 5 V is the one that needs level shifting.

Full pin tables for both shift registers and the in-shell cable connector are in the component library below. The house-part problem is easier to see next to the alternatives: Controllers: How Five Consoles Read a Button puts this pad beside the NES, Genesis and N64 designs.

On conductive paint. When a carbon contact pad has genuinely worn through rather than just dirtied, paint is the repair of last resort and it does work. Clean first and be sure: isopropyl only, never an abrasive and never a fibreglass pen, because both strip the carbon layer permanently and turn a dirty pad into a worn one. If paint is warranted, keep it thin and off the surrounding traces: the patches above are thicker than I would like, and a blob that bridges to a neighbouring trace creates a stuck input. Replacement pad sets and silicone membranes are the tidier fix where they exist.

Chip and connector pinouts

The component library: each IC and connector defined once, with an interactive pin diagram where the package is drawable and a folded pin table underneath. The revision badge on each card shows which board or boards it applies to. The Nintendo ASICs carry only the handful of pins the mod literature actually names, because Nintendo never published a pinout for them.