Super Nintendo Troubleshooting Guide
This guide provides detailed, component-level troubleshooting for the Super Nintendo Entertainment System (SNES). It covers all major motherboard revisions (SHVC, SNS-CPU, SNS-RGB, etc.) and notes differences between NTSC and PAL models where relevant. Common failure symptoms, diagnostic procedures, and fixes are outlined for:
- Power supply faults
- No video / black screen
- RAM (Work RAM, Video RAM) issues
- Video encoder (S-ENC, BA6592F, S-RGB) faults
- Audio (SPC700, S-DSP, S-SMP, DAC) faults
- CPU (Ricoh 5A22) faults
- PPU (Picture Processing Unit) faults
- Controller port and input issues
- Cartridge slot and connection problems
Diagnostic techniques (visual inspection, voltage and signal probing, chip substitution, thermal checks), voltage test points (+5 V, +12 V), and critical signals (RESET, clock, data/address lines) are all explained.
Note: This guide does not cover Super Famicom Box, Satellaview, or SNES CD add-ons.
Diagnostic Tools & Techniques
[edit | edit source]Visual Inspection
[edit | edit source]- Remove the top cover; inspect for burnt, cracked, or bulging components, corrosion (especially near the cartridge slot and AV port), and cold solder joints—notably around the power jack, voltage regulator, and controller ports.
- Re-solder any suspect joints to resolve intermittent power or input issues.
Thermal Checks
[edit | edit source]- After 1–2 minutes of power-on, gently touch (or use an IR thermometer) on major chips (CPU, PPU1, PPU2, S-ENC/S-RGB, RAM).
- Chips that are hot to the touch (much hotter than others) may be internally shorted.
- Use freeze spray or compressed air: if the system behaviour changes when cooling a specific IC, that chip is likely faulty.
Power & Signal Probing
[edit | edit source]- +5 V DC: Confirm at voltage regulator output and at Vcc pins of major ICs (CPU, RAM, PPU, etc.).
- +12 V DC: Present only on some early models (for video encoder); check at regulator and relevant ICs.
- RESET: Should pulse low briefly at power-on, then remain high (5 V).
- Clock signals: Check for 21.47727 MHz (NTSC) or 21.28137 MHz (PAL) at crystal and CPU/PPU clock pins.
- Data/address bus activity: Use logic probe or oscilloscope to confirm activity on CPU, RAM, and PPU pins during power-on.
Chip Substitution
[edit | edit source]- Swap socketed chips (where applicable) one at a time with known-good parts:
- CPU (5A22)
- PPU1/PPU2
- Work RAM (SRAM)
- Video RAM (VRAM)
- S-ENC/S-RGB video encoder
- For surface-mount chips, use a donor board or hot-air rework for replacement.
Common Symptoms & Solutions
[edit | edit source]| Symptom | Possible Cause | Diagnostic Steps | Solution |
|---|---|---|---|
| No power / no LED | Blown fuse, faulty power supply, bad power jack, failed voltage regulator | Check fuse for continuity; measure voltage at power jack and regulator input/output | Replace fuse, repair/replace power supply, re-solder or replace jack/regulator |
| No video / black screen | Bad cartridge connection, failed CPU/PPU, faulty RAM, video encoder fault, broken trace | Clean cartridge slot; check for clock/reset at CPU; probe video encoder output; inspect for broken traces | Clean slot, reflow/replace encoder, repair traces, swap suspect chips |
| Distorted or no audio | Faulty S-SMP/SPC700, S-DSP, DAC, bad caps, broken AV port | Test audio at AV port; inspect caps; probe S-SMP/SPC700 pins for activity | Replace caps, reflow/replace audio ICs, repair AV port |
| Random freezes / crashes | Failing RAM, intermittent cartridge connection, overheating ICs | Run with known-good cartridge; probe RAM for activity; check chip temps | Replace RAM, clean slot, improve cooling, replace overheating chips |
| No controller response | Bad controller port, broken traces, failed CPU or input buffer | Test with known-good controller; inspect port and traces; check CPU input pins | Reflow/replace port, repair traces, swap CPU if necessary |
| Corrupted graphics / sprites | Bad VRAM, PPU1/PPU2 fault, video encoder issue | Probe VRAM/PPU pins; check for bus activity; try chip cooling | Replace VRAM, swap PPU chips, replace encoder if needed |
Notes on Major Components
[edit | edit source]- CPU (5A22): Handles main processing; failure causes no-boot or erratic behaviour.
- PPU1/PPU2: Video output; faults cause graphical glitches or no video.
- Work RAM (SRAM): 128 KB; failure causes crashes, freezes, or corrupted operation.
- Video RAM (VRAM): 64 KB; faults cause graphical corruption.
- S-ENC / S-RGB: Video encoder; failure causes no video or distorted colours.
- S-SMP, SPC700, S-DSP: Audio subsystem; faults cause missing or distorted sound.
- Voltage Regulator: Converts input to +5 V (and +12 V on some boards); failure causes power issues.
Test Points & Voltages
[edit | edit source]| Location | Expected Voltage |
|---|---|
| Power jack (center pin) | +9 V DC (unregulated) |
| Voltage regulator output | +5 V DC |
| CPU/PPU Vcc pins | +5 V DC |
| AV port pin 3 (composite video) | 1–2 V (video signal) |
| AV port pin 8 (audio) | 0.5–2 V (audio signal) |
Warnings
[edit | edit source]- Always power off and unplug before working inside the SNES.
- Be careful not to bridge pins or damage traces when probing or soldering.
- Some chips (especially PPU1/PPU2) are not socketed and require advanced soldering skills to replace.