Super Nintendo Troubleshooting Guide

This guide covers fault-finding on the Super Nintendo Entertainment System and its Japanese equivalent the Super Famicom. Its figures come from Nintendo's own service literature for the machine — the Playtronic Manual Técnico do Super NES and the Japanese Famicom / Super Famicom / Game Boy service manual, both hosted on this wiki. Where a figure is not in one of those, it is not given here.

For preventive care, the connector work and the GPM board changes see Super Famicom Maintenance Guide; for capacitor values by board revision see Super Famicom Capacitor Replacement Guide.

Super Famicom Box, the Satellaview and the unreleased CD add-ons are not covered.

Discharge C67 before you open it

Nintendo's first disassembly instruction is not about screws:

Before disassembling, switch the console's power supply ON with the AC adapter disconnected, in order to discharge capacitor C67. This capacitor is known to discharge during maintenance, causing damage to components.

C67 is the reservoir on the DC input and it holds its charge after the adapter is out. Flicking the power switch with nothing plugged in empties it through the console's own load. On a GPM board there is no C67 — Nintendo deleted it in that revision — but the step costs nothing and you do not always know which board you have until it is open.

Power

The NTSC and Japanese consoles take 10 V DC at 850 mA, centre negative. Centre negative means the centre pin is 0 V and the outer sleeve is positive. PAL consoles take 9 V AC and rectify it on the board. The two are not interchangeable in either direction.

The supply is unregulated. The Famicom-family HVC-002 adapter, which the Super Famicom also uses, is specified by Nintendo to read DC 13.5 ± 1.5 V off-load, and Nintendo's power-circuit block diagram labels the 7805's input arm 13–14 V. A high off-load reading is normal and is not a reason to replace the adapter.

Power test points

Where	Expected	Note
Adapter, no load	12.0–15.0 V DC	Nintendo's figure is 13.5 ± 1.5 V
Plug polarity	Centre 0 V, sleeve positive	A centre-positive supply of the right voltage will destroy the console
F1	Continuity	A 1.5 A SSTR axial fuse. Both Nintendo parts lists carry it
U12 (7805) input	13–14 V off-load, sagging under load	U12 is the regulator on SHVC-CPU boards; on 1CHIP and SNN boards the same part is at U9
U12 output — Vcc	5.0 V DC	The only regulated rail in the machine. The CPU, PPU1, PPU2 and APU all run from it and nothing else
Vs — unregulated	~7 V by Nintendo's figure; near 9 V by measurement	Feeds only the audio amplifier. The console runs without it, silently

There is no +12 V rail and no 3.3 V rail in a Super Nintendo. If you are probing for one, stop. "IC601" is not a designator on any of these boards either — the regulator is U12, or U9 on the later single-chip boards.

Clocks and reset

Nintendo's own description of the timing section: a 21 MHz master clock goes to the CPU, to PPU1 and PPU2 and to connector P1. The CPU divides it by 6, 8 and 12 to give 3.58, 2.68 and 1.79 MHz; the CPU core runs at 3.58 MHz, address-mapped transfers at 2.68 MHz, and DMA always at 2.68 MHz regardless of address.

The exact master frequency depends on the region and the wrong figure will send you chasing a fault that is not there:

Master clock by region

Region	Frequency
NTSC (North America, Japan)	21.47727 MHz
PAL (Europe, Australia)	21.281370 MHz
PAL-M (Brazil, Playtronic)	21.453666 MHz

Nintendo's Brazilian manual specifies the TC1 adjustment at 21.453666 MHz because it is a PAL-M manual. Do not apply that figure to an NTSC or European machine.

The reset section is a 4 MHz oscillator (X2), a 74HCU04 hex inverter, the CIC and the reset switch. Nintendo gives the acceptable 4 MHz range as 3.8 to 4.2 MHz. The CIC's reset is applied to PPU2 first, which introduces a delay, then passed to PPU1 and only then to the CPU — both PPUs must be running before the CPU is released.

That ordering is diagnostically useful: a fault that holds PPU2 in reset stops the whole machine, and looks identical to a dead CPU.

On a GPM board the 4 MHz oscillator was removed along with C67, and Nintendo's manual states the timing and reset sections differ there.

Nintendo's order of suspicion

Where Nintendo's fault tree names a component, it names these:

• F1, the 1.5 A fuse — dead console.
• U12, the 7805 — dead console, or a 5 V rail that is low or absent.
• X1, the 21 MHz oscillator — no picture, or a picture that cannot be brought into adjustment at TC1.
• X2, the 4 MHz oscillator — the CIC cannot run, so the console will not start.

If TC1 cannot be adjusted or the adjustment will not hold, Nintendo's replacement sequence starts with the oscillator at X1.

Symptom table

Symptom	Work through, in order
Completely dead — no LED	Adapter off-load reading and polarity → DC jack and its solder joints → power switch → F1 continuity → U12 input and output.
LED on, black screen, no sound	Clean the 62-pin connector and the cartridge edge, and retest with a second cartridge. Then 5 V at the CPU and both PPUs → 21 MHz at X1 → 4 MHz at X2, within 3.8–4.2 MHz → reset released. Remember the reset order: PPU2, then PPU1, then CPU.
Picture, no sound	The audio amplifier runs from the unregulated rail, not the 5 V rail. Check that rail before suspecting the sound module. A console with a healthy 5 V rail and a dead unregulated rail plays silently but otherwise normally.
Wrong or missing colours	Nintendo prints a dedicated colour-fault tree; it is reproduced on Super Famicom Maintenance Guide. Check the AV lead and the television first.
Picture cannot be tuned, or drifts	TC1, against the region-correct master frequency. If it will not hold, X1.
Corrupted sprites or backgrounds, Mode 7 wrong	VRAM, then PPU1 and PPU2. A PPU that fails only on Mode 7 effects is a documented pattern, so test a Mode 7 title before clearing the PPUs.
Freezes, or works only with the cartridge pressed	The 62-pin connector. Nintendo supplies it as two service parts, an upper and a lower half, so a damaged one can be replaced.
Power cuts out when a cartridge is removed	Not a fault on earlier consoles. The power switch carries an anti-eject lever that rides in a notch in the cartridge; on cartridges with a diagonal notch it switches the console off as the cartridge comes out. Nintendo deleted the lock bar on GPM machines and replaced it with a warning label.

Probing, safely

• Do not measure ICs with a multimeter or a signal tracer. Nintendo's own handling notes say plainly that the test voltage a meter applies will damage the device, and that if you must measure an IC's resistance you should use the lowest range and accept the risk.
• The power switch harness is polarised. Nintendo marks + and − on the switch body and specifies the red lead to + and the black to −. Reversing it is a self-inflicted fault created during reassembly.
• The front unit's FFC goes in one way round. The unprinted side is the contact face; the blue-printed side is not. Fitting it reversed gives dead controller ports on a console that is otherwise fine.
• The console opens with six security screws in the lower case, taking a 4.5 mm Gamebit driver. The sound module, where fitted, comes off with two screws and lifts vertically.

Thermal checks

After a minute or two, a device markedly hotter than its neighbours is usually shorted internally. Freeze spray is the complementary test. The 7805 is meant to run hot — it is dropping 8 V or so at whatever the console draws, and that is where the heat goes.

Related pages

• Super Nintendo Entertainment System
• Super Famicom Maintenance Guide
• Super Famicom Capacitor Replacement Guide
• Nintendo Super NES Technical Manual (Playtronic, Rev. 01-94)
• Nintendo Famicom Service Manual
• SNES Schematic
• Recommended Tools