• Right deck & mixer

    Adam Trizuljak01/06/2022 at 17:05 0 comments

    The left deck was a success, so I removed all remaining knobs from the controller and removed the right deck and mixer PCB. Note that the volume fader and crossfader knobs use a locking mechanism, removing them is also shown in Cameron Gray's teardown video. This is the PCB after removing it from the case:

    The process to replace the LEDs is exactly the same as with the left deck, in fact I didn't even bother to take a picture after swapping them. While I was here I also considered to replace the red LEDs in the audio level indicator, because they too are pretty dim. But it turned out that the replacement LEDs don't illuminate the level indicator window evenly, they were causing a hot spot in the middle. It didn't look good, so I abandoned this idea.

    Again, let's take a moment to appreciate some clever engineering. All buttons on the controller are constructed as levers where the actual switch is placed at the lever's end. Mechanical advantage is used in two ways: first, to reduce the force applied to the actual switch (did I already mention that these controllers get abused like there's no tomorrow?). And second, it also reduces the travel distance required to actuate the button, which provides faster and snappier response to the DJ who is trying to hit the buttons exactly on the beat. The lever also incorporates depth stops that are just long enough to allow the switch to be actuated, but then they come in contact with the PCB which prevents excess force from being applied to the switch itself.

    At this point I tested that all LEDs are working and I proceeded to re-assemble the controller. I thought I was done, but then I noticed that all potentiometer knobs were misaligned by about 2mm to the side. Everything was working fine, but the asymmetrical knobs looked just terrible. So it was back to loosening all 70+ screws and carefully aligning both PCBs. I started with the left deck, only slightly tightening screws 1 and 2 and adjusting the PCB until I was happy with the position of the Headphones Mixing and Level knobs. Then I tightened screws 1 and 2 (being careful not to shift the PCB around) and then I tightened all the remaining screws in their designated order. Then I repeated the same process with the large right deck PCB. It took me an hour of fiddling to get the alignment just right, and having an electric screwdriver probably saved my wrist from an RSI.

    Previously I mentioned that the new green Play button LEDs were a bit too bright, so before closing the controller I decided to change their resistors (R1465 and R2489) from the original 270R to 680R. This makes them less retina-piercing in the dark, but they remain very well visible even in sunlight. The Cue buttons now were a bit dim, so I also changed their resistors (R1432 and R2416) from 150R to 100R. All resistors are SMD 0603 size. The good thing is that the resistors are accessible just by removing the rear cover of the controller, you don't have to disassemble the PCBs.

    Here you can see the modified resistors on the left deck vs. the original right deck.

    And that's it! Honestly, swapping the LEDs is pretty easy and takes less than an hour, but the disassembly, alignment and re-assembly were much more tedious than I expected. But in the end I really enjoy the brighter pads, it was totally worth the effort. The design of the controller makes it pretty easy to repair, replace broken components or perform modifications.

  • Left deck

    Adam Trizuljak01/02/2022 at 11:30 0 comments

    After opening the case we see that the DDJ-400 is split into two main PCBs that host all the potentiometers / faders, buttons and LEDs. The larger PCB (on the left side in the next photo) combines both the right deck and the mixer section and contains many potentiometers and faders, all of which have knobs that have to be removed before the PCB can be pulled out. The left deck PCB is smaller and hosts only one fader and two potentiometers. These boards are connected to the main logic board via flat flex cables.

    Since the left deck is much easier to remove, I decided to start with its LEDs as a trial run to see if the intended modification works as desired. Be careful when removing the knobs, you don't want to scratch your controller or even worse, break a potentiometer. Cameron Gray suggests to use a key cap puller, I used two metal spudger tools to symmetrically pry the knobs upwards.

    We first have to remove the headphone jack board, the logic board and carefully disconnect the flat flex cables. Then we remove the screws and are greeted by a rather simple-looking PCB:

    I started by swapping just one LED to have a comparison of how it looks. In the picture below, the left LED is the stock, right is the replacement. Rather annoyingly, the new LEDs don't have the flat side to indicate polarity and the larger internal metal pad is the anode (instead of cathode, which is more typical) - I'll have to pay careful attention to the polarity. Below they are shown running in series on an LED tester at about 1mA current. Already much brighter!

    Notice that the LEDs leads are bent outwards to provide better mechanical reinforcement to the connection. These DJ controllers take a lot of abuse, which is also why they use so many screws to make the entire unit as rigid as possible. The bent leads are a bit of a challenge for desoldering, as they must be first heated up and bent back up before they can be desoldered. Luckily I have a desoldering station, which makes it pretty easy to do. After removing and swapping the LED:

    Then I partially re-assembled the controller with just a few screws to hold the PCB in place and I re-connected the main logic board. Success! The camera actually makes the old LEDs appear brighter than they really are, but in person the difference in brightness is huge.

    I was very happy with the result, so it was back to disassembling the PCB and replacing all LEDs of the left deck, including the Sync and Play buttons. First I desoldered the old LEDs, my desoldering station helped to greatly speed up the process.

    When inserting the LEDs, I bend their leads outwards like the rest of the components. To make sure that the LEDs are nice and square, I first add some solder to one lead to temporarily tack it in place. Then I re-heat the connection while pressing the LED with a finger against the PCB to properly seat it. Then I fully solder in both leads and trim the excess length from the leads.

    All LEDs replaced:

    And everything partially re-assembled to show the difference:

    This was shot at night with regular room lighting. The camera slightly over-emphasizes the old pads, but the pads of the left deck are much brighter in person. The Play button is perhaps a bit too bright, I think I will just change the 270R current limiting resistor to something higher. The resistor is easily accessible without having to remove the PCBs from the controller.

    This is during the day with indirect light. The left deck LEDs are clearly visible, whereas the right deck LEDs are basically invisible. Of course, even the new LEDs are swamped out when the sun shines directly on the pads, but you can see them if you just shade them with your hand. With the old LEDs, you would struggle to see them even while shaded. You could in theory use even brighter LEDs, but I think that they would eventually become too bright for night time use.

    Everything is looking good, next step is to modify the right deck....

    Read more »

  • Disassembly and LED selection

    Adam Trizuljak01/02/2022 at 01:00 0 comments

    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%).