When I realized that the LEDs are not very bright, I started wondering if they could be replaced. And indeed, I found an excellent teardown video by Cameron Gray which shows the disassembly process, the individual circuit boards and the electronic components. The disassembly is fairly straightforward, however the unit is held together by about 60 screws in order to keep the plastic body rigid. An electric screwdriver is definitely your friend here :)

Once disassembled we see that the PCBs are only single-sided and resemble a mid 2000's piece of AV equipment with jumper wires and through-hole LEDs, buttons and other components. All buttons are backlit by standard 3mm LEDs. This is great news! Also while we are here, let's just admire how modular and repairable the DDJ-400 is. The entire PCB is marked with component names, polarity indicators and even signal names. With a bit of soldering experience, just about any component could be replaced. In addition, all screws are numbered to show you the correct assembly sequence - this is important for properly aligning the PCB inside the plastic body.

With this knowledge I started to look for suitable LED alternatives. My criteria were:

• Red color to keep with the original color theme
• As bright as possible (>3000mcd)
• Relatively wide viewing angle to nicely illuminate the rubber buttons

I settled for LITEON LTL1CHVRTNN (rated 1500-3200mcd at 20mA; 631nm typ. wavelength, 45° viewing angle). The high intensity rating plus the shorter wavelength should make these LEDs appear much brighter than the stock ones. You could probably choose even higher brightness LEDs without issues. You will need 1 LED per performance pad, 2 LEDs for each of the rectangular pad mode buttons and 1 LED for the Sync button, that's 34 LEDs for the entire controller.

While I was at it, I also decided to replace the Play button LEDs. I don't like its standard yellow-green color, which to me in person looks very close to the orange color of the Cue button. Either I am slightly color-blind, or somebody didn't put a lot of effort into choosing nice LED colors during the design phase. Anyway, I chose LITEON LTL17KCGM4J with a lime-green color between 514-527nm.

I chose to stick with the original red color theme but you could definitely get very creative with the LED colors. I think an all-white LED mod would look cool, you could also apply a white vinyl sticker skin for a very unique look. Or you could use a different colored LED for each performance pad and trick your DJ friends that your DDJ-400 has RGB performance pads, just like its bigger brothers the DDJ-800 and DDJ-1000. Just one warning: it would be tempting to use slow-fade RGB LEDs, but this likely will not work since all LEDs are multiplexed and run at a low duty cycle (~10%).