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Super Nintendo Entertainment System Audio Circuit Repair

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SNES audio mixer, mute and output stage (Donaldson redraw)
The mixer, mute and output stage of the NTSC GPM and RGB boards, from Jonathon W. Donaldson's redraw. Audio enters at the left and leaves through Q16 and Q17 at the right.

When a Super Nintendo Entertainment System plays a picture with distorted sound or none, Nintendo's diagnostic table names, most likely first, the sound module, its connector P5, the CPU (U1), the amplifier (U10) and Q18.[1] On the original board the sound processor, DSP, digital-to-analogue converter and sound RAM sit on a plug-in sound module; later boards carry the same circuit on the main board. The DAC's output goes through an op-amp amplifier, which also mixes in audio from the cartridge slot and the expansion port, to the stereo pins of the Multi Out; the RF modulator and the expansion port get a mono mix.[2] The amplifier runs from the unregulated Vs rail, not the 5 V logic supply, so a console with a dead Vs rail plays games normally in silence.[3]

The checks below follow the audio from the DAC to the Multi Out on the NTSC GPM and RGB boards, which the redraw covers, one stage at a time.[4]

Symptoms

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Sound faults and where to start
Symptom Start at
No sound at all, picture normal Vs (stage 1)
No sound through the Multi Out, sound on RF The output stage and Multi Out pins (stages 5 and 6)
One channel missing The pre-amplifier and mixer section for that channel (stages 3 and 4)
Distorted sound The sound module on an SHVC-CPU-01 (Nintendo's first suspect), then stages 2 to 5

Nintendo's own triage is to retest the console with a known-good sound module before repairing the board.[5] Its self-test cartridge puts the sound module first and the CPU second for an APU error.[6]

Safety

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The console runs on the adapter's low voltage. Discharge C67 before opening it by switching on with the adapter disconnected.[7] Measure voltages, not resistances, on the ICs: Nintendo warns that a meter's resistance ranges can damage them.[8]

Tools and parts

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  • A multimeter and an oscilloscope. A scope shows whether audio is present at each stage while a game plays music.
  • A cartridge that plays continuous music on its title screen.
  • For an SHVC-CPU-01, a known-good sound module. Nintendo Japan priced the module as a replacement assembly.[9]
  • Replacement parts as the fault shows: LM324 op-amp, 2SC2412 transistors.[4] Nintendo's SHVC-CPU-01 parts list has an LM358 amplifier and ten 2SC2412 transistors.[10]

The signal path

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SNES audio DAC and pre-amplifier (Donaldson redraw)
The DAC U17 and the two pre-amplifier sections. ROUT (pin 6) feeds U100D, whose output is pin 14; LOUT (pin 11) feeds U100C, whose output is pin 8.
Audio path on the NTSC GPM and RGB boards
Stage Part Left Right
1 Vs supply from Q18 Feeds the LM324 and the output transistors Q16 and Q17
2 DAC U17 (uPD6376) LOUT, pin 11 ROUT, pin 6
3 Pre-amplifier (LM324) U100C, output pin 8 U100D, output pin 14
4 Mixer (LM324) U100A, output pin 1 U100B, output pin 7
5 Output follower Q17 Q16
6 Multi Out P4 Pin 11 Pin 12

Source: the redraw.[4] The mixer adds the cartridge and expansion-port audio to the DAC's, which is how cartridges with their own sound chips are heard.[4][2]

Procedure

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Opening the console

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Open the console and expose the main board as on the cartridge connector guide. On an SHVC-CPU-01, the sound module is held by two screws on its far side and lifts straight up.[7] Refit the controller board and the power switch lead so the console can be run with the board exposed.

Super NES sound module lifted out (Nintendo ASC manual)
The plug-in sound module of an SHVC-CPU-01 being lifted out

Stage 1: Vs

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  1. Run a game and measure Vs, at the emitter of Q18 or the collectors of Q16 and Q17. Nintendo gives Vs as about 7 V; the redraw's sheet note says 9 V.[2][4]
  2. If Vs is missing while the 5 V supply is present, check Q18, R76 and C64; see the power circuit guide.[4] Nintendo lists Q18 last among the causes of distorted or missing sound.[1]

Stage 2: the DAC

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  1. With music playing, look at LOUT (pin 11) and ROUT (pin 6) of U17 on the scope.[4]
  2. If both are flat, the fault is before the DAC: the sound processor, DSP, sound RAM or DAC. On an SHVC-CPU-01 these are on the sound module, which Nintendo replaces first; reseat it and try a known-good module.[1][5] On the boards without a module, Nintendo's order continues with the CPU.[1]

Stage 3: the pre-amplifier

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  1. Follow each channel through its filter to the pre-amplifier output: U100C pin 8 for left, U100D pin 14 for right.[4]
  2. Audio at the DAC but not at a pre-amplifier output points at that LM324 section or its filter parts (R99 and R101 to R105, C74 to C79).[4]

Stage 4: the mixer and mute

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  1. Check the mixer outputs: U100A pin 1 for left, U100B pin 7 for right.[4]
  2. If audio reaches the mixer inputs on both channels but neither output, look at the mute circuit. Q14 and Q15 sit on the mixer inputs and are switched by the MUTE line, which Q13 makes from the S-DSP's /MUTE output; the redraw notes that Q13 inverts the signal.[4]
  3. A single dead channel with the other working points at that channel's half of the LM324, its 1 µF input capacitor (C26 left, C23 right) or its mute transistor (Q15 left, Q14 right).[4]
SNES Multi Out connector P4 (Donaldson redraw)
The Multi Out connector P4: audio left on pin 11, right on pin 12, ground on pins 5 and 6

Stages 5 and 6: the output

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  1. Check the emitters of Q17 (left) and Q16 (right), then pins 11 and 12 of the Multi Out.[4][3]
  2. Audio at the mixer output but not at the emitter: the transistor or its 1 kΩ emitter resistor (R65 left, R58 right).[4]
  3. Audio at the emitter but not at the Multi Out pin: the 1 kΩ output resistor (R70 left, R67 right) or the track and pin.[4]
  4. The RF output carries a mono mix of both channels through further resistors, so sound on RF with nothing on the Multi Out narrows the fault to the Multi Out side.[2][4]

Testing

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  1. Play a cartridge with stereo music and listen to each channel separately on the Multi Out.[5]
  2. Run Nintendo's console test, which checks the stereo output in A/V mode and the RF output on channels 3 and 4.[5]

Board differences

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Audio circuit by board
Board Difference
SHVC-CPU-01 Sound processor, DSP, DAC and RAM on the plug-in SHVC-SOUND module on connector P5;[2][4] Nintendo's parts list has an LM358 amplifier,[10] and the redraw's note puts an LM2904 on the module as pre-amplifier and another on the main board[4]
SNS-CPU-GPM-01/02, SNS-CPU-RGB-01/02 The circuit traced above, on the main board[4]
Cost-down boards Sound processor, DSP and RAM combined in the S-APU, and an S-MIX A at U10, which fullsnes takes to be the sound amplifier.[3] The redraw does not cover these boards

The SHVC-SOUND module also carries two 47 µF electrolytics, C50 and C51; see the Super Famicom Capacitor Replacement Guide.[11]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, p. 2-28 (console diagnostic table, "distorted or no sound": sound module, connector P5, U1 CPU, U10 amplifier, Q18, in order of priority), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, p. 2-2 (sound section: a sound module holding the sound processor (SMP), the DSP, a D/A converter and two 256K RAMs, and a sound amplifier; the amplifier takes inputs from the expansion connector P6, the 62-pin connector P1 and the sound module; its left and right channels use LM358 op-amps whose outputs become the stereo output of the multi-out connector P4; the RF modulator and expansion connector outputs are mixed to mono) and p. 2-1 (Vs, 7 V unregulated, used by the sound amplifier), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  3. ↑ 3.0 3.1 3.2 Martin Korth, fullsnes (retrieved 2026-10-25). "SNES Power Supply": the audio amplifier runs from the unregulated supply, and the console works without it but makes no sound. "SNES Audio/Video Connector Pinouts": Multi Out pin 11 audio left, pin 12 audio right, 5 V peak to peak; pins 5 and 6 ground. "SNES Chipset": cost-down boards with the S-APU (S-SMP, S-DSP and sound RAM) at U2 and an S-MIX A at U10, described as "maybe sound amplifier?". Community reference.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 Jonathon W. Donaldson, Super Nintendo (NTSC) Revision 2 Motherboard (w/ Revision 1 SHVC-SOUND connector), community redraw, rev. 1.5, 24 February 2014, hosted at SNES Schematic as File:Snes schematic.pdf. Covers SNS-CPU-GPM-01/02 and SNS-CPU-RGB-01/02. Audio: U17 uPD6376 DAC (LOUT pin 11, ROUT pin 6); pre-amplifier LM324 sections U100C (left, output pin 8) and U100D (right, output pin 14) with 22 kΩ filters; analogue mixer U100A (left, output pin 1) and U100B (right, output pin 7) summing APU, cartridge and expansion audio through 1 µF capacitors C23 to C28 and 10 kΩ resistors, with 24 kΩ feedback and a reference from VS through R50 33 kΩ and R51 24 kΩ with C61 10 µF; mute transistors Q14 and Q15 switched by MUTE, derived by Q13 from the S-DSP's /MUTE (pin 39); emitter followers Q16 and Q17 on VS; outputs through R66 to R71 to the mixed audio, mono and RF feeds; Multi Out P4 pin 11 Audio-L and pin 12 Audio-R. Power: Q18 2SC2412 with R76 1.8 kΩ and C64 33 µF feeding VS. Note on the sheet: the first-revision board has two LM2904 dual op-amps, one on the SHVC-SOUND module as pre-amplifier and one on the main board as post-amplifier, and connector P5 is the SHVC-SOUND connector. Not a Nintendo document.
  5. ↑ 5.0 5.1 5.2 5.3 Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, p. 2-23 (console test procedure: test the stereo output in A/V mode, and before any repair to the PCB retest with a known-good sound module and a known-good upper 62-pin connector), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  6. ↑ Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, p. 2-24 (console tester self-test 1: replacement priority for an APU error, sound module then CPU), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  7. ↑ 7.0 7.1 Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, p. 2-14 (discharge C67 with the adapter disconnected; sound module held by two screws on its far side and lifted straight up), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  8. ↑ Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, pp. 8-1 and 8-2 (do not test ICs with a multimeter or signal tracer), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  9. ↑ Nintendo, ファミコン・スーパーファミコン・ゲームボーイ サービスマニュアル (Famicom / Super Famicom / Game Boy Service Manual), 1992, p. 15 (Super Famicom repair price list: item 2, sound module; item 3, sound module exchanged for an IC fault), hosted at Nintendo Famicom Service Manual.
  10. ↑ 10.0 10.1 Nintendo / Playtronic, Manual Técnico do Super NES, Rev. 01/94, p. 2-6 (SHVC-CPU-01 parts list: LM358 SOP, transistors 2SC2412 ×10, sound module) and p. 3-3 (GPM parts list: transistors 2SC2412 ×10), hosted as File:Manual Tecnico do Super NES Rev 01-94.pdf.
  11. ↑ Altomare, snes-capacitors, GitHub (retrieved 2026-10-25). SHVC-CPU-01: C50 and C51, 47 µF 10 V radial, on the SHVC-SOUND module, with at most 8 mm between the board and the shield.
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