A known issue with the legacy m904 and m906 monitor controllers is the occasional failure of their level readout LEDs. You will know if yours are bad because individual segments of the digits will start to go dark making the character illegible. This replacement kit includes all 6 LED modules for both the ‘headphone level’ and ‘main level / edit’ character displays.
The replacement procedure is quite simple and only requires removing four screws, unplugging the bad LEDs and plugging in the new LEDs – no soldering or specials tools are required. The full procedure can be found here.
$25 + shipping