SNES:Super Game Boy Clock Speed Mod
The original release of the Super Game Boy runs about 4% faster than an original Game Boy. This is most noticeable in the audio playback, but it also means that the SGB is not allowed for use in speed-running, and is part of the reason why there is no link port available, since the speed difference would cause the communication to desync. The later Japan-only Super Game Boy 2 fixed this problem by installing a crystal oscillator running at the correct speed.[1] Multiple DIY mods exist to fix this problem by replacing the timing crystal with a corrected one, as well as at least one pre-assembled mod board.
Qwertymodo's Board
Qwertymodo sells a pre-made quick-solder board (QSB) that corrects the clock speed while also preserving all features of the Super Game Boy such as speedup and slowdown using Hori gamepads. The product can be found on Tindie or at Qwertymodo's store with more in-depth documentation on it found on their personal website.