Nintendo Entertainment System Controller Repair
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The standard controller of the Nintendo Entertainment System has one integrated circuit, a 4021 CMOS 8-bit shift register with parallel inputs and a serial output. Each of its eight inputs is held high by a 45 kΩ resistor and goes to ground through an open contact surface on the PCB; pressing a button pushes a conductive pad onto that contact surface and grounds the input. The console reads the buttons by sending OUT0 to load the register and CUP clock pulses to shift the eight bits out on DO.[1] The faults are almost all mechanical: worn or dirty pads and contacts, a broken cable, and less often a failed 4021.[1] By 2002 Nintendo's service centres no longer repaired the standard controller; its manual lists it among accessories that are not cost-effective to repair and exchanges it instead.[2]
Symptoms
[edit | edit source]| Malfunction | Probable cause | Nintendo's repair procedure |
|---|---|---|
| Slow response | Worn contact pads | Inspect the pads for damage or excessive wear |
| Slow response | Dirty or damaged contact surfaces on the PCB | Inspect the contact surfaces for contamination or damage |
| Random or no response | Worn contact pads | Inspect the pads for damage or excessive wear |
| Random or no response | Defective 4021 | Remove the 4021 and test it |
| Random or no response | Defective cable | Test the cable for electrical integrity |
| Random or no response | Defective PCB | Inspect the PCB for cracks or damaged traces |
Source: Nintendo's workbook, which also tells the servicer to take the controller apart and inspect the housing, cable, contact pads, PCB and button actuators for damage and dirt before starting any repair.[1] One repairer found that a faulty 4021 made a controller mix up buttons, so that pressing jump paused Super Mario Bros. 3.[3]
If a known-good controller also fails in the same port, the fault is in the console: Nintendo's table for the NES-001 lists the 40368 buffers, the CPU, the protection arrays DA1 to DA4 and RA1 and RA2 for input port errors. See the Nintendo Entertainment System Troubleshooting Guide.[4]
Tools and parts
[edit | edit source]- A small Phillips screwdriver and a container for the screws.[5]
- Isopropyl alcohol or distilled water, cotton swabs, a microfibre cloth or paper towel, and a pencil eraser.[5]
- Soap and warm water for the shell and buttons.[5]
- For electrical repairs: a soldering iron, a desoldering pump and a multimeter.[3]
- Replacement parts where needed: rubber pads, a controller cable, or a 4021 shift register. Dreamcast.nu fitted an MN4021B.[3][1]
Procedure
[edit | edit source]Disassembly
[edit | edit source]- Unplug the controller from the console.
- Remove the six screws from the underside and lift off the back.[5][1]
- Lift the cable off the posts it is wrapped round as a strain relief, then lift out the circuit board.[5]
- Lift out the three rubber pads that sit under the board, and the buttons if you are washing the case.[5]
Cleaning
[edit | edit source]- Inspect the pads, the board's contact surfaces, the cable and the case for damage and dirt.[1]
- Rub the circular contacts on the board gently with a pencil eraser, then wipe the board with alcohol on a cotton swab. Do not sand the contacts; it wears them and can damage the board.[5]
- Clean the carbon contacts on the underside of the rubber pads with a little alcohol or distilled water on a cloth or swab. Do not use anything harsher, which can degrade the rubber.[5]
- If a button still misbehaves after cleaning, rub its pad's carbon contact two or three times across a sheet of plain paper. This wears the contact, so do it only when needed.[5]
- Replace any pad that is torn or broken.[3]
- Wash the case halves and buttons in soap and warm water and let everything dry thoroughly, about an hour.[5]
Replacing the cable
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Nintendo numbers the five cable positions on the controller board as follows.[1]
| Position | Signal | 4021 pin |
|---|---|---|
| 1 | GND | 8 |
| 2 | CUP (clock) | 10 |
| 3 | OUT0 (latch) | 9 |
| 4 | DO (data out) | 3 |
| 5 | VCC | 16 |
- Before desoldering the old cable, use the multimeter to note which pin of the plug each of the five board positions connects to.[3][1]
- Desolder the old cable from the board.[3]
- Find which wire of the new cable goes to which pin of its plug with the multimeter. The colours differ between cables, so do not go by colour.[3]
- Solder each new wire to the board position whose plug pin matches your notes from the first step.[3]
Replacing the 4021
[edit | edit source]- Desolder the 4021 from the board; a manual desoldering pump is enough.[3]
- Fit the new 4021 the same way round as the old one, with its pin 1 matching, and solder it in.[3][1]
Reassembly
[edit | edit source]- Push the buttons back into the front case.[5]
- Lay the rubber pads over the buttons, carbon side up.[5]
- Lay the board on the posts over the pads, chip side up.[5]
- Route the cable round the posts as it was before.[5]
- Fit the back and refit the six screws. Tighten them only until the case holds together.[5]
Testing
[edit | edit source]- Nintendo tested controllers in either port with its NES Joystick Test Cartridge, pressing every button separately and together; each button's area on the screen turns from red to green while it is pressed.[1] Without that cartridge, plug the controller in and test every button in a game.[5]
- To find a dead button with a meter, connect the controller to a console that is switched on and measure the 4021 input for that button against ground. The 45 kΩ pull-up holds it high, and pressing the button should pull it low.[1]
| Button | 4021 pin |
|---|---|
| A | 1 |
| B | 15 |
| Select | 14 |
| Start | 13 |
| Up | 4 |
| Down | 5 |
| Left | 6 |
| Right | 7 |
If the pin goes low when the button is pressed but the console still does not see it, suspect the 4021 or the cable; if it does not go low, clean the contact and the pad again or replace the pad.[1]
Related pages
[edit | edit source]- Nintendo Entertainment System
- Nintendo Entertainment System Troubleshooting Guide
- Nintendo Entertainment System General Maintenance
- NOA Independent Servicer Technical Training Workbook
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Nintendo of America, NOA Independent Servicer Technical Training Workbook, Rev. 11/90, "NES Controller Operation", p. 8; controller exploded view, p. 9; "Controller PC Board Schematic", p. 10; "Controller Testing and Troubleshooting", p. 11 (PDF pages 14 to 17). Hosted as File:NES WCS HQ.pdf; see NOA Independent Servicer Technical Training Workbook.
- ↑ Nintendo of America, Authorized Service Center Manual, revision June 2002, chapter 2, "Accessories": "The following are not cost effective to repair", including the NES Standard Controller, P/N 21637 (p. 15). Hosted as File:Nintendo Authorized Service Center Manual June 2002.pdf.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 Dreamcast.nu, "NES controller repair", 25 April 2021. Six screws in the back; cleaning plastics with soap and water and the PCB with alcohol; replacing rubber pads; replacing the cable, identifying the new cable's wires with a multimeter because colours vary between cables; replacing the MN4021B, and the mixed-up buttons it caused.
- ↑ Nintendo of America, NOA Independent Servicer Technical Training Workbook, Rev. 11/90, "Malfunctions and Probable Causes", "Input Port Error", p. 54. Hosted as File:NES WCS HQ.pdf.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 Dave Farquhar, "Fix NES controllers yourself", The Silicon Underground, updated 22 January 2025. Tools; six screws on the underside; the cable wrapped round posts as a strain relief; three rubber pads under the board; cleaning the board contacts with a pencil eraser and alcohol and not sanding them; cleaning the pads with alcohol or distilled water and rubbing them on paper; washing the shell; drying for about an hour; reassembly order and cable routing; not overtightening the screws.