Here are a few general things we can do:
General fault finding & Repairs
Composite / Rgb / Hdmi mods
Calibrate / repair laser
Replace the old capacitors in your system (recapping)
Silent Fan mods
Replace power supply with a good & reliable 12V solution (NO PICOPSU CRAP !)
Creation of repro carts
Replace the Game cart save battery
Lcd repacement in Handhelds (GBA, GBC, DMG, GAMEGEAR, ...)