Step 4: Adding the SMDs
For these LEDs there are two ends, a positive and negative. If the LED is backwards, it simply won't turn on. If it is correctly connected it will light up when you power on the controller. Microsoft seems to like changing the markings for every 360 controller mainboard. The marking used always identifies the negative terminal. The markings I have seen are either a white circle, a green arrow (on this controller), or just the LED location (D1, D2, D3, D4). Worst come to worst, there are only two directions to install the LED, one of them will light up. In general Player 2, 3, and 4 the negatives are on the clockwise end, while Player 1 has the negative on the counter-clockwise end. Every controller seems to be different.
The 0603 SMD LEDs have markings that also denote the negative terminal. I have attached a picture below showing the three markings used.
Installing Your SMD
Decide upon the LED you are going to replace. Line up the LED and grip it on the sides with your tweezers, not too hard or you can crack the LED, making that LED useless. Applying too much heat to the LED can toast the wire inside, causing it to light up very brightly and become a dud. Use short exposure times (Under 2 seconds). An oddity with this mod is some tweezers can build up a static charge that fries the LEDs, before picking them up, just tap your tweezers to a block of metal (only needs to be done once to remove the initial charge).
To install your SMD to the mainboard, apply a small dab of solder to your iron, while using the tweezers to position your LED over the terminals, solder one of the terminals correctly (usually the negative to the negative). One bond will hold it in place, making it easy to connect the other. You can now reassemble the controller (except for the motors and screws), reinsert the battery pack, and hit the power on button. Normally all four LEDs blink when you turn on a controller, hopefully it will turn on. If it doesn't, either the LED is not soldered to both terminals, is soldered backwards, or the controller isn't put back together properly (the power button can't reach the board). After each LED has been soldered, wipe off the excess solder on your iron with a wet sponge or towel. When it lights up, repeat the process for all four terminals.