Avalanche v4.2 Photo Build Log
You can get the hardware from one of the following links.
Flash the following firmware on the both controller breakout boards by QMK Toolbox.
avalanche_v4_default_with_rgb_and_via.hex
75KB
Binary
avalanche_v4_vial.hex
77KB
Binary

W1 is for serial. Bridge W1 on the left and right hand side.
For OLED displays, bridge the 4 jumper pads on the top side. Do not bridge them on the bottom side.

Top of Left and Right Hand Side

Top of the Left Hand Side

Top of the Right Hand Side

Bottom of the Right Hand Side

Bottom of the Left Hand Side

Bottom of the Right Hand Side
Diodes are directional. Pay attention to the bottom row and the diodes placed horizontally.

Short pin headers vs standard pin headers
Short pin headers or sockets are recommended.

Top of the Left Hand Side

Top of the Right Hand Side

Top of the Left and Right Hand Sides

Bottom of the Left Hand Side

Bottom of the Right Hand Side
Insert the pin headers and controller boards according to the silk screen.
You can test the single side with VIA or a web-based keyboard tester by shorting the hotswap socket solder pads. It's recommended to test all key presses before moving to the next step.

Top of the Left Hand Side

Bottom of the Left Hand Side

Top of the Right Hand Side

Bottom of the Right Hand Side
Now, you can connect the both halves and test if they are sending the right key presses.

Top of the Left Hand Side

Bottom of the Left Hand Side

Bottom of the Right Hand Side
The switch is to to enable/disable the power supply for the OLED display and RGB LEDs.
Set it to the "on" state, and plug it into the computer. The OLED screen should display some text. If it doesn't work, toggle the switch and reconnect it to the computer. The on state for the left side is the opposite of that of the right side.

Bottom of the Left Hand Side

Bottom of the Right Hand Side
The switch sockets are directional. Leave the switch slot empty if you decide to use an encoder. Encoders are optional, and you can use at most one encoder on a single side.

Top of the Left and Right Hand Sides
RGB LEDs are optional. Before soldering the RGB LEDs, make sure you have a fully working keyboard.

RGB LEDs are Directional.
RGB LEDs are directional. Align the corner to the silk screen mark.

Bottom of the Left Hand Side
Solder the first RGB LED (L7). It should light it when you connect it to the computer.

Bottom of the Left Hand Si
Disconnect the keyboard from the computer. Repeat the above step for L8, L9, L10, ..., L38.
An RGB LED is also required when the slot is used for an encoder. Alternatively you can bridge the DIN/DOUT pins.

Bottom of the Left Hand Side
It's recommended to solder them in order, with 3-5 LEDs each time and test.