SNES:Audio Balance Fix

Due to an odd oversight, older SNES and Super Famicom consoles have a slight audio imbalance issue which can be easily corrected. This issue was first discovered by Ace around 2018/2019.

Overview

On earlier board revisions, both the left and right audio channels are slightly out of balance, with the left channel being slightly louder than the right. This problem lies in the voltage reference (Vref) pins of the NEC uPD6376 DAC (digital to analog converter) chip and how they are connected. The DAC has two Vref pins (one for each audio channel), which according to the datasheet, are each supposed to be connected to a 47 uF capacitor, which is then connected directly to ground at the negative end. This is done in order to properly set the impedance for each audio channel. However, Nintendo connected both Vref pins to a single 47 uF capacitor, going against the datasheet. Because of this, the impedance for both channels is incorrect and an audio imbalance is created. The following board revisions are affected:

• SHVC-CPU-01
• SNS-CPU-GPM-01
• SNS-CPU-GPM-02
• SNSP-CPU-01
• SNSP-CPU-02
• SNS-CPU-RGB-01

Later board revisions use a different DAC that only has a single Vref pin, eliminating this issue.

Fortunately, it is fairly simple to correct this problem by isolating just one of the Vref pins, connecting it to the positive lead of a 47 uF capacitor, and then wiring the negative lead to ground.

Materials and Tools

Materials

• 47 uF capacitor, preferably 10V or higher
  • Note that if you are performing this fix on an SHVC-CPU-01, get the smallest capacitor possible as space is very tight inside the SHVC-SOUND module.
• Leaded solder
• Flux (optional, but highly recommended)

Tools

• 4.5 mm gamebit screwdriver
• JIS/Phillips head screwdriver
• Soldering iron
• Tweezers
• Razor blade
• Flush cutters
• Wire stripper
• Multimeter

Procedure

1. Flip over the console and unscrew the six 4.5 mm gamebit screws, then remove the top case and set it aside.
2. Further disassembly will differ depending on board revision:
   • On the SHVC-CPU-01, unscrew the two JIS/Phillips screws securing the sound module (labeled SHVC-SOUND) and disconnect it from the motherboard. Set the rest of the console aside. Once the sound module is removed, pry off the bottom half of the shielding. This will expose all of the components inside.
   • On all other board revisions, a more thorough disassembly is needed. Remove the two screws securing the power switch and disconnect it from the motherboard, then remove the eject mechanism and the screws securing the motherboard to the bottom case. Once the motherboard is removed, undo the screws for the heat sink so the board is fully exposed.
3. Next, either pin 9 or 10 of the DAC must be isolated from the rest of the board. On the SHVC-SOUND module, you will need to lift pin 9 as the trace connecting pins 9 and 10 runs underneath the DAC. On all others, cut the trace between pins 9 and 10. This will leave pin 10 isolated.
4. With pin 10 (or pin 9 on the SHVC-SOUND module) isolated, take a 47 uF capacitor and solder the positive lead to the pin. Be sure to cut the capacitor lead as short as possible to avoid shorting it to the rest of the board.
5. Solder the negative lead of the capacitor to ground, which can be found at various places.
   • On the SHVC-SOUND module, pin 26 of the S-SMP chip is a convenient source for ground, or the right side of C14 (make sure you connect to the ground side, check with a multimeter).
   • On all other boards, ground can be tapped at the negative lead of the 47 uF capacitor located next to the DAC (this is the capacitor for the other Vref pin that was not isolated) or pin 5, 12 or 14 of the DAC.
6. Reassemble the console and test.