Nintendo 64 Audio Output Repair

Audio section of an NUS-CPU-03 board: the BU9480F DAC (U1), the AMP-NUS amplifier (U2) with pins 1, 7, 8 and 14 numbered on the silkscreen, and the electrolytics C24, C25, C26, C28, C33 and C142

The Nintendo 64 sends stereo sound to pins 11 (left) and 12 (right) of its multi-out connector, P7. On the NUS-CPU-01 to -04 mainboards a Rohm BU9480F DAC (U1) converts the digital audio from the RCP, and an AMP-NUS amplifier (U2), powered from +12 V, drives the two outputs through coupling capacitors. From NUS-CPU-05 the DAC is built into the AVDC-NUS or MAV-NUS video chip, but the AMP-NUS remains: one owner who replaced it was working on an NUS-CPU-09-1 board.

Owners who have lost the sound while the picture stayed good have traced the fault to the multi-out solder joints, to the output and supply capacitors, and to C28 on the amplifier; some have bypassed the amplifier altogether. Designators and values below are from RDC's schematic of the NUS-CPU-03 and -04 mainboards, N64 NUS-CPU-03-04 Schematic; other revisions may differ.

Symptoms

• No sound from either channel, with a normal picture.
• Sound that crackles, plays for a second or two and then cuts out.
• Sound or picture that cuts in and out when the AV lead is moved at the console: a cracked joint at the multi-out.

These look similar but are not board faults:

• The audio leads plugged into the TV's outputs instead of its inputs, a mono TV with only one audio lead connected, or the TV's mono or stereo setting. Some games start their sound only after START is pressed.
• Silence straight after switching on. N64brew notes that audio may not start until about ten seconds after the game is running.
• No picture and no sound with the power LED lit. That is a no-boot fault: see the Nintendo 64 Troubleshooting Guide. The AMP-NUS and the video encoder both depend on the +12 V input (the encoder through the 78M05 regulator U13, which makes +5 V from it), so a missing +12 V rail takes out sound and picture together.

Safety

The console itself runs on the +3.3 V and +12 V that the external AC Power Supply delivers; mains voltage is present only inside that supply. The checks below are made on a running board with its shields off. N64brew notes that with the cover off the console should run without its heat shrouds and heatsinks for a while, but gives no guarantee; keep these runs short. Pin 1 of the AMP-NUS carries +12 V and sits next to pins that do not: a slipped probe on that chip shorts the rail across them.

Tools and parts

• 4.5 mm Gamebit and cross-head drivers to open the console; see Nintendo 64 Mainboard Replacement.
• Multimeter. An oscilloscope to follow the audio signal; N64brew uses one on the audio output.
• Fine-tipped soldering iron, flux and desoldering braid; hot air if U2 has to come off.
• Surface-mount aluminium electrolytics to the schematic values: 10 µF 16 V for C25 and C26, 33 µF 25 V for C24, C28 and C142. The same values apply at those positions on every NTSC revision in the Nintendo 64 Capacitor Replacement Guide.
• A replacement AMP-NUS can only come from a donor board.

The audio path

Audio and video output section of RDC's NUS-CPU-03/04 schematic. U1 (bottom left) feeds the AMP-NUS U2 through C32 and C31; U2's outputs leave through C25 and R58 (left) and C26 and R57 (right) to pins 11 and 12 of P7 (right).

Audio signal path on the NUS-CPU-03/04 schematic

Stage	Parts	What to check
DAC	U1, BU9480F. Inputs LRCK (pin 5), SDAT (pin 6) and BCLK (pin 7); outputs L-OUT (pin 4) and R-OUT (pin 1); VCC pin 8 from +3.3 V; REF pin 2 to ground through C33 (68 µF 10 V)	+3.3 V on pin 8; audio on pins 4 and 1 while a game plays
Coupling to the amplifier	C32 (100 nF, left) and C31 (100 nF, right), with R20 and R18 (10 kΩ) from the DAC outputs to ground	Audio on both sides of C32 and C31
Amplifier	U2, AMP-NUS. Inputs LIN and RIN; outputs LOUT and ROUT; VCC from +12 V; LF and RF to ground through C24 and C28 (33 µF 25 V each); LIN2 and RIN2 take the left and right audio lines from Game Pak connector P5 pins 24 and 49 through C30 and C29 (100 nF), with R21 and R17 (200 Ω) to ground on the connector side; the pin labelled 13 to ground through C34 (10 µF 16 V), with R19 (180 kΩ) and D1 on the same node	+12 V on VCC; audio on LOUT and ROUT
Output coupling	LOUT through C25 (10 µF 16 V) and R58 (1 kΩ) to P7 pin 11; ROUT through C26 (10 µF 16 V) and R57 (1 kΩ) to P7 pin 12; C23 (left) and C122 (right) from the output lines to ground, values not given on the drawing	Audio at P7 pins 11 and 12

All values and connections in the table are from the schematic; N64brew names P5 pins 24 and 49 LAUDIO and RAUDIO. The schematic names the AMP-NUS pins by function only. The pin numbers used below are the ones owners give in the iFixit thread, read off the silkscreen, which numbers pins 1, 7, 8 and 14 at the corners of U2.

Procedure

Rule out the cable and connector

1. Connect a known-good AV cable with both audio leads to the TV's audio inputs, and check the TV's mono or stereo setting.
2. Start a game and wait at least ten seconds for the sound.
3. Move the AV lead at the console end while the game plays. If the sound cuts in and out with the movement, reflow the multi-out joints (below) before anything else.

Open the console and reflow the multi-out

1. Remove the top cover and the shields as in Nintendo 64 Mainboard Replacement.
2. Remove the plastic plate over the A/V area: undo its left and right screws, lift the mainboard slightly and pull the plate off.
3. Reflow the joints where the six metal strips of the multi-out connector meet the board, using flux.

Check the amplifier's supply

NUS-CPU-03 output section: P7 at the top, U13 with its VI (+12V) and VO (+5V) labels, and U2 lower right

1. With the console running, measure +12 V at the VI (+12V) side of U13 and +5 V at its VO (+5V) side; both labels are printed on the board beside the regulator.
2. Measure from U2 pin 1 to ground. Pin 1 is the +12 V supply pin; the corner pin is marked 1 on the silkscreen.
3. If +12 V is missing at U2 but present at U13, look for a broken trace between them. If it is low everywhere, check C142 (33 µF 25 V on the +12 V rail) and the supply.

Trace the signal

1. With a game playing, follow the audio with the oscilloscope from U1 pins 4 and 1, through C32 and C31, to the AMP-NUS inputs, then from the AMP-NUS outputs through C25, R58, C26 and R57 to P7 pins 11 and 12. On NUS-CPU-05 and later boards there is no U1; start at the AVDC-NUS or MAV-NUS.
2. The stage where the signal stops is the faulty one. Signal at the AMP-NUS inputs but none at its outputs points to U2, its supply, or C24 and C28.

Output and supply capacitors

1. Unplug the supply. Measure across C25, C26 and C142 for a short; Sarmatios suggests these three as a cause of lost sound. A reading across C142 is a reading across the whole +12 V rail.
2. Replace any shorted or leaking part with the same value and voltage, with the negative mark the same way round; the method is in the Nintendo 64 Capacitor Replacement Guide.

C28

On Julian Turner's NUS-CPU-09-1 board, a known-good replacement AMP-NUS and new capacitors from the amplifier to the multi-out did not bring the sound back. His probe then slipped while he was measuring pin 1 and briefly shorted +12 V into pin 2, and the sound returned. Pin 2 goes to ground through C28 and nowhere else, so he concluded that C28 was the faulty part; the sound was still working two and a half years later. Several other owners in the thread report the same result from the same short. Victor L.F. removed C28 and got the sound back. On an NUS-CPU-08-01 board, Hill Bass measured about 2 Ω from U2 pin 2 to ground; the short produced a spark and no sound, and removing C28 restored both channels. On the schematic, C28 is the 33 µF 25 V capacitor on the AMP-NUS RF pin, and the can on the board is printed 33.

1. Do not short pin 1 to pin 2. It puts the +12 V rail straight onto C28 and the amplifier pin, and it did not work on every console.
2. Unplug the supply and measure from U2 pin 2 to ground. A reading of a few ohms, like Hill Bass's 2 Ω, means C28 has failed short.
3. Remove C28, the 33 µF can below U2 to the right of C24.
4. Fit a new 33 µF 25 V capacitor with the same polarity. Hill Bass gives 330 µF as the replacement; the schematic and the marking on the original can both say 33 µF.

Bypassing the amplifier

Where U2 itself has failed and no donor is available, owners have bypassed it. Sarmatios desoldered U2 and bridged its pads 3 to 7 and 8 to 12, using the numbers printed on the board, and noticed no loss of volume or quality. The schematic does not number the AMP-NUS pins. Read in the order it draws them, which agrees with pin 1 being VCC and pin 2 the RF pin as Turner found, those pairs join RIN to ROUT and LOUT to LIN, leaving C25, C26, R57 and R58 in circuit. Pixlvamp found that bridging the pads did not work on his console and instead wired U2 pin 7 to P7 pin 12 for the right channel and pin 8 to P7 pin 11 for the left. That wiring skips C25, C26, R57 and R58 as well as the amplifier.

Turner points out what a bypass gives up: the output is the DAC's unamplified audio, and the AMP-NUS also mixes in audio from the cartridge and expansion port, which is lost. Find the real fault first.

Testing

• Play a game and listen to each channel separately.
• Nintendo's service centres checked the sound with the N64 test cartridge's audio test, which speaks on the left channel, then the right, then plays music through the left, the right and both together.
• Refit the shields and heatsink before a long session.

Related pages

• Nintendo 64
• Nintendo 64 Troubleshooting Guide
• Nintendo 64 Maintenance Guide
• Nintendo 64 Capacitor Replacement Guide
• Nintendo 64 Video Output Repair
• Nintendo 64 Mainboard Replacement
• N64 NUS-CPU-03-04 Schematic