My recapped Game Gear had a problem with scraping sound when adjusting the volume with the volume control. There is a relatively straight forward way to fix that: replacing the volume control wheel. To do so, you need some basic soldering skills and tools. The volume control is a 10KA (log) Potentiometer. My potentiometer was a bit slimmer than the original, but that is not a problem: it feels the same as the original. In the images below, I go through the process of replacing the volume wheel.
First, disassemble your unit by removing six philips-screws, and one gamebit screw.Then, disattach the two cables between the audio board and the main unit, and the cable going to the power board as well. There are two philips screws holding the audio board in place. Remove them. One is under the metal shield, so you have to remove that as well.Here is the (recapped) Game Gear audio board.This is the area we want to desolder. Five tiny points in a line, and two additional points at the top. I used my desoldering gun here.Now, solder the replacement potentiometer into place. Done! Reverse the process to assemble your Game Gear again, and enjoy the sound!