Nintendo Entertainment System Troubleshooting Guide
Fault-finding on the front-loading NES-001 and top-loading NES-101 versions of the Nintendo Entertainment System starts with Nintendo's own material. Its fault table and test procedure for the NES-001 are in its World Class Service technician's workbook, and its consumer leaflet lists the common causes it told owners about; both are reproduced below.[1][2] The Famicom has its own page, Nintendo Famicom Troubleshooting Guide.
For the chip map, test points and cartridge connector care, see Nintendo Entertainment System General Maintenance. For capacitor lists, see Nintendo Entertainment System Capacitor Replacement Guide.
Preliminary checks
[edit | edit source]Nintendo's leaflet gives these causes, most common first.[2]
| Symptom | Most common causes | Action |
|---|---|---|
| Snowy screen | Wrong hookup to the TV | Check the hookup |
| Solid colour or blank screen | Dirty connectors; on a new console, both the VHF and the audio/video inputs connected | Clean the Control Deck connector and game pak edge; use one hookup |
| Scrambled screen | Dirty connectors | Clean the connector and game paks |
| Blinking or flashing screen; blinking power light | Game pak not inserted properly; dirty connectors | Push the game pak fully in and down; clean the connector and game paks |
| No power light | Power button not on; adapter not plugged into the console or a live outlet; non-Nintendo adapter | Check the switch, adapter and outlet |
| Picture fine, no sound | AV cable hookup; some game paks are silent until play starts; TV volume or mute | Check the hookup and TV |
| Picture fine, sound buzzes or is distorted | AV cable hookup; RF switch and AV cable both connected | Use one hookup, not both |
Clean the connector and the cartridge before probing anything; on an NES-001 a bad contact can give a blank screen, scrambled graphics or a reset loop. Do not blow on the cartridge edge.[2][3]
Nintendo's fault table
[edit | edit source]Nintendo's workbook lists these probable causes for the NES-001 control deck, in this order, after a test with its port test fixture and cartridge, Super Mario Bros. and Duck Hunt. It tells the servicer to inspect the board for cracks, damaged components and damaged traces first.[1]
| Malfunction | Probable causes |
|---|---|
| No control deck operation | RF modulator; power/reset switch assembly; PCB |
| Excessive current draw or 60 Hz buzz | RF modulator; IC(s); crushed capacitors; PCB |
| No reset, display normal | CIC; power/reset switch assembly; C8 or C9 (replace C8/C9); PCB soldering |
| Display keeps resetting | CIC; 7404; 4 MHz oscillator; power/reset switch assembly; PCB soldering |
| No power light | 7404; CIC; 4 MHz oscillator; power/reset switch assembly; PCB soldering |
| Input port error (port test cartridge) | 40368(s); CPU; DA1 to DA4; RA1 or RA2; PCB soldering |
| Normal display; no, low or distorted audio | CPU; 7404; RF modulator; PCB soldering |
| Games lock up or jump to other parts of the program | CPU; WRAM; 74139; RA1 or RA2; PPU |
| Solid colour or blank display, no sound | 21 MHz oscillator; CPU; WRAM; 74139; RA1 or RA2; PPU; VRAM |
| Solid colour or blank screen with sound | PPU; VRAM; 74373; CPU; Q2; RF modulator |
| Scrambled video | PPU; VRAM; 7404; 74373; CPU |
On the NES-001, U9 is the 7404 (74HCU04), U10 the CIC, U1 the WRAM, U4 the VRAM, U2 the 74373, U3 the 74139 and U7 and U8 the 40368s. C8 and C9 are on the CIC: C9 (2.2 µF) on pin 3 and C8 (0.1 µF) on pin 7.[1][4]
Power
[edit | edit source]Both the NES-001 and the NES-101 take the NES-002 adapter, rated 9 V AC at 1.3 A.[5] Measure it on the meter's AC range. With no load it reads above 9 V, which is normal for a plain transformer. The console rectifies and regulates the supply itself; game-tech.us has run an unmodified NES-101 from 9 V and 12 V DC adapters as well as the NES-002.[6]
On the NES-001 the rectifier, reservoir and AN7805 regulator are in the RF modulator module. Nintendo's schematic gives the voltages at its connectors:[1]
| Connector | Pin | Signal | Voltage |
|---|---|---|---|
| P3 (RF modulator) | 1 | Video | about 1.45 V DC |
| P3 | 2 | Audio | about 2.55 V DC |
| P3 | 3 | Vcc | about 5 V DC |
| P3 | 4, 5 | PS2, PS1 (supply to the power switch) | about 10.65 V DC |
| P6 (power/reset switch board) | 1, 2 | PS1, PS2 | about 10.65 V DC |
| P6 | 3 | Vcc | about 5 V DC |
| P6 | 4 | Reset | about 0 V DC |
| P6 | 5 | Power LED | about 3.2 V DC |
Compare readings with Nintendo's figures, with the console switched on. On the NES-101 the 7805 is on the mainboard: U9 on the NESN-CPU-01 board, and U7 on the later NESN-CPU-JI0-01 and NESN-CPU-AV-01 boards according to Console5.[7] Then check +5 V at RP2A03 (U6) pin 40, with ground on pin 20.[8]
Blinking power light
[edit | edit source]On the NES-001 a blinking power LED with a blank or flashing screen is the CIC lockout chip (U10) resetting the console because it could not talk to the matching chip in the cartridge. A dirty connector causes this as often as an unlicensed cartridge does, and Nintendo's leaflet lists cartridge seating and dirty connectors as the causes.[2][3] If cleaning, reseating and the connector alignment described on Nintendo Entertainment System General Maintenance do not cure it, Nintendo's table points at the CIC, the 7404, the 4 MHz oscillator and the power/reset switch board.[1] Console5 disables the lockout by cutting pin 4 of the chip marked CIC.[3]
The NES-101 has no lockout chip and does not show this fault.[7]
On the 1989 schematic set hosted as NES Schematics, U10 takes RESET on pin 7 and drives the system reset from pin 9, its clock comes from a 4 MHz crystal and sections of U9 on pin 6, and CIC1, CIC2 and CIC10 on pins 1, 2 and 10 go to the cartridge edge.[9]
CPU pins
[edit | edit source]| Pin | Signal | Note |
|---|---|---|
| 1 | AD1 | Audio: both pulse channels |
| 2 | AD2 | Audio: triangle, noise and DPCM |
| 3 | /RST | Reset, active low |
| 29 | CLK | 21.47727 MHz master clock in (NTSC); the CPU divides it by 12 |
| 31 | M2 | The divided CPU clock, about 1.79 MHz on NTSC |
| 35, 36 | /OE2, /OE1 | Read enables for controller 2 and controller 1 |
| 39 | OUT0 | Controller strobe |
| 20 | GND | |
| 40 | +5 V |
From NESdev.[8] The sound generator is inside the CPU; there is no separate sound chip. Nintendo's table lists the CPU, the 7404 and the RF modulator for missing or distorted audio, and the audio reaches the modulator on P3 pin 2.[1]
The 4021 shift register that reads the buttons is inside each controller, so try another controller before probing the console.[10] On the NES-001 the controller data passes through U7 and U8 (40368) and the protection parts DA1 to DA4 and RA1 and RA2, which is why Nintendo lists them for input faults.[1]
Model differences
[edit | edit source]| NES-001 (front loader) | NES-101 (top loader) | |
|---|---|---|
| Cartridge connector | 72-pin zero-insertion-force connector with a spring carrier | 72-pin edge connector, 68 positions populated |
| Lockout | CIC at U10 | None |
| Regulator | AN7805 in the power/RF module | 7805 on the mainboard (U9 on the NESN-CPU-01) |
| Video out | RF and composite A/V | RF only, except a small number of factory A/V units |
| Adapter | NES-002, 9 V AC | NES-002, 9 V AC |
Vertical lines in the NES-101's picture are a characteristic of the machine, not a fault.[7] NTSC consoles use the RP2A03 CPU and RP2C02 PPU; PAL consoles use the RP2A07 and RP2C07, with a 26.601712 MHz master clock.[11]
Related pages
[edit | edit source]- Nintendo Entertainment System
- Nintendo Entertainment System General Maintenance
- Nintendo Entertainment System Capacitor Replacement Guide
- NES-001 Schematic
- NES Schematics
- NOA Independent Servicer Technical Training Workbook
- Nintendo Famicom Troubleshooting Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Nintendo of America, World Class Service Authorized Servicer Technical Training Workbook (running header "NOA Independent Servicer Technical Training Workbook", Rev. 11/90). Hosted as NOA Independent Servicer Technical Training Workbook. Control deck testing procedure, pp. 53-54; "Malfunctions and Probable Causes", pp. 54-55; RF Switch operation, p. 56; Appendix B (unnumbered): control deck schematic with P3 and P6 voltages (PDF pages 93-94) and section descriptions (PDF page 97).
- ↑ 2.0 2.1 2.2 2.3 Nintendo of America, Product Maintenance, Troubleshooting and Service Guide (World Class Service leaflet). Hosted as Nintendo World Class Service NES Product Maintenance Troubleshooting And Service Guide. Maintenance tips and NES troubleshooting table.
- ↑ 3.0 3.1 3.2 Console5 TechWiki, "Improving NES-001 Reliability" (retrieved 2026-10-01).
- ↑ Console5 TechWiki, "Nintendo NES-001" (retrieved 2026-10-01). Chip map and test points.
- ↑ Evan-Amos, "Nintendo-Entertainment-System-NES-Power-Supply.jpg", Wikimedia Commons, public domain. Rating plate: "Output AC9V 1.3A", "for use with NES Control Deck No. NES-001 & NES-101 only".
- ↑ game-tech.us, "NES-101 Power Research" (retrieved 2026-10-01). Power draw of an unmodified NES-101 from the NES-002 9 V AC adapter and from 9 V and 12 V DC adapters; the 7805 bolted to a heatsink and the 1500 µF reservoir.
- ↑ 7.0 7.1 7.2 Console5 TechWiki, "Nintendo NES-101" (retrieved 2026-10-01). NESN-CPU chip maps; no CIC; vertical lines in the video.
- ↑ 8.0 8.1 NESdev Wiki, "CPU pinout" (retrieved 2026-10-01).
- ↑ NES Schematics, 1989 CAD schematic set, sheet 1 (NESMB1.SCH, rev. A, 12 July 1989), author not recorded. Hosted as NES Schematics (PDF).
- ↑ NESdev Wiki, "Standard controller" (retrieved 2026-10-01).
- ↑ NESdev Wiki, "PPU variants" (retrieved 2026-10-01).
