Nintendo 64 Video Output Repair

Video output section of an NUS-CPU-03 board: the multi-out P7 at the top, the 220 µF output capacitors C15 and C16, the VDC-NUS video DAC (U4), the ENC-NUS encoder (U5) and the 78M05 regulator U13 with its VI (+12V) and VO (+5V) labels

The Nintendo 64 has no RF output of its own. Its multi-out connector, P7, carries composite video on pin 9 and S-Video luma and chroma on pins 7 and 8. On the NUS-CPU-01 to -04 mainboards the RCP's digital video passes through a VDC-NUS DAC (U4), which produces red, green and blue, and an ENC-NUS encoder (U5), which turns them into composite and S-Video. Later boards combine both jobs in one chip: the DENC-NUS on the first PAL board, the AVDC-NUS on early NUS-CPU-05 boards and the MAV-NUS after that.

Owners who have lost the picture while the sound kept working have found the cause in the multi-out's own solder joints and in the parts between the encoder and the connector. Designators and values below are from RDC's schematic of the NTSC NUS-CPU-03 and -04 mainboards (N64 NUS-CPU-03-04 Schematic) unless a later board is named.

Symptoms

• No picture on composite, S-Video or both, with sound present.
• A very faint picture. On blueapple's NUS-CPU-08 board the composite output looked like a 5 V DC level with a faint video signal on it, and a CRT showed a rolling picture only when its input was switched from 75 Ω to 1 kΩ.
• Picture and sound that cut in and out when the AV lead is moved: cracked joints at the multi-out.

These look similar but are not faults:

• NUS-CPU-04 boards have no composite sync on P7 pin 3. The schematic marks the sync circuit "-03 ONLY", so an RGB cable that takes its sync from pin 3 gives no picture on an -04.
• PAL NUS-CPU(P)-03 and -03-1 boards have no S-Video: the luma and chroma traces from the MAV-NUS to the multi-out are cut and the parts are not fitted.
• PAL boards do not have C15 and C16 fitted; see the lists on the Nintendo 64 Capacitor Replacement Guide. One EEVblog poster states that PAL consoles leave out R5 to R7 and C14 to C16 altogether.
• A black screen with no sound is a no-boot fault, covered in the Nintendo 64 Troubleshooting Guide.

Safety

The console 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 some time, but gives no guarantee; keep the runs short.

Tools and parts

• 4.5 mm Gamebit and cross-head drivers to open the console; see Nintendo 64 Mainboard Replacement.
• Multimeter. An oscilloscope for following the video signal; N64brew probes the composite output with one.
• Fine-tipped soldering iron, flux and braid.
• Parts as needed: 220 µF 10 V surface-mount electrolytics for C15 and C16, and 75 Ω resistors for R5 to R7. The schematic gives no value for C14; an EEVblog poster gives 68 nF. On later boards, a 75 Ω resistor array matching the one fitted at RA1.

The video path

Video section of RDC's NUS-CPU-03/04 schematic (top half). U4 (left) feeds U5 through C124 to C126; U5's outputs leave through C15, C16 and C14 and the 75 Ω resistors R5, R6 and R7 to P7 (right).

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

Stage	Parts	What to check
Video DAC	U4, VDC-NUS: digital video in on D0 to D6, clock on CLK; RED, GRN and BLU out, each loaded to ground by 110 Ω (R8, R9, R10); SYNC and BFP out to the encoder; VCC from +3.3 V	+3.3 V at VCC; signal on RED, GRN and BLU
Encoder input	C124, C125 and C126 (1 µF) to U5 RIN (pin 3), GIN (pin 2) and BIN (pin 1); SYNC to pin 5, BFP to pin 6; colour subcarrier to SCIN (pin 8) through C21	Signal on pins 1 to 3; subcarrier on pin 8
Encoder	U5, ENC-NUS: VCC1 (pin 4) and VCC2 (pin 14) from +5 V; GND1 (pin 7) and GND2 (pin 11); outputs YOUT (pin 13), VOUT (pin 12) and COUT (pin 10)	+5 V at pins 4 and 14; signal on pins 10, 12 and 13
Output protection	Diode array DA6 on VOUT and YOUT; DA8 on COUT	No short from any output line to ground
Output coupling	VOUT through C15 (220 µF 10 V) and R5 (75 Ω) to P7 pin 9 (composite); YOUT through C16 (220 µF 10 V) and R6 (75 Ω) to pin 7 (S-Video Y); COUT through C14 and R7 (75 Ω) to pin 8 (S-Video C); C13, C12 and C11 from those lines to ground, values not given on the drawing	Signal at P7 pins 7, 8 and 9

All connections and values in the table are from the schematic. The colour subcarrier is a quarter of the X1 crystal frequency: 3.58 MHz on NTSC boards and 4.43 MHz on PAL boards.

Procedure

Rule out the cable and connector

1. Try a known-good AV or S-Video cable and another TV input.
2. Move the lead at the console end while the console runs. If the picture comes and goes, reflow the multi-out (below) first.

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, and test again.

Check the supplies

1. With the console running, measure +12 V at the VI (+12V) side of U13 and +5 V at its VO (+5V) side. The encoder runs from that +5 V.
2. On NUS-CPU-01 to -04 boards, measure +5 V at U5 pins 4 and 14 and +3.3 V at U4's VCC pin.

Measure the output network

1. Unplug the supply. Measure each output line from P7 pins 7, 8 and 9 to ground. A low reading means a shorted filter capacitor (C11 to C13) or diode array (DA6, DA8) on that line.
2. On early boards, check R5, R6 and R7 for 75 Ω in series between the capacitors and the connector.
3. On a later board with a MAV-NUS, measure the resistor array that terminates the video outputs. On blueapple's NUS-CPU-08 it was RA1, marked "750", and MAV-NUS pin 29 (Y), pin 27 (composite) and pin 25 (C) should each read 75 Ω to ground through it. He measured it in circuit, and an open resistor was obvious against the good ones. The designator may differ on other revisions.

Trace the signal

1. With an oscilloscope, look at P7 pin 9 at least ten seconds after switching on. A black screen still produces a signal, so activity alone does not prove the encoder is working.
2. On early boards, follow the missing output back: R5, C15 and U5 pin 12 for composite; R6, C16 and U5 pin 13 for luma; R7, C14 and U5 pin 10 for chroma.
3. If all three outputs are missing at U5, check its inputs on pins 1 to 3, the sync and burst signals on pins 5 and 6, and the subcarrier on pin 8. Signal present at the inputs with nothing at the outputs points to U5 or its +5 V supply.
4. If U5 has no input, go back to U4's RED, GRN and BLU outputs and the 110 Ω loads R8 to R10.

Repair

1. Replace a failed capacitor at C14, C15 or C16 with the same value and voltage, the negative mark the same way round.
2. Replace an open 75 Ω resistor, or a resistor array with an open element. blueapple restored the picture on his NUS-CPU-08 by replacing RA1, without replacing the MAV-NUS or recapping the board.
3. Where the MAV-NUS itself has failed, no new parts are sold. Another owner in the same thread got a picture back by fitting an HDMI kit that takes the video digitally and so bypasses the console's DAC.

Testing

• Check composite and S-Video separately, on a CRT if possible.
• Nintendo's service centres checked the picture with the N64 test cartridge: red, green and blue full screens, colour bars, five moving and still patterns, and interlace on and off.
• 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 Audio Output Repair
• Nintendo 64 Mainboard Replacement
• N64 NUS-CPU-03-04 Schematic