Hi!
At first you need to know THERE ARE NO "5W" Epistar chips. How the lights are labelled depends on how the LEDs are driven and how efficient they are. (As I understand, different bins of chips etc.)
This is where I got my replacement chips from, the "3W" Epistar chips:
1 - 30 pcs 1W 3W High Power LED without PCB - Grow lights aquarium Heatsink | eBay
So you need to know what type you need, for my light I had to figure this out myself, there is Royal Blue, Bright Blue, Bright Red, Deep Red and Warm White. (When you make a photo of the lamps turned on you can with some luck see which LEDs are the Royal (Darker) Blue, Deep Red and Bright Red. It's subtle but it's possible to see).
*** When you solder, make sure you you have a good soldering iron. I had a soldering iron with a screw sticking out sideways from the top. I melted MORE LEDs in my pathetic attempt to solder than I fixed because I accidentally touched working LEDs with the screw. So I soldered in 4 replacements and while doing so melted FIVE others. Incredible pathetic, lol, fortunately I had enough replacement LEDs handy. With a DMM (digital multi meter) you can test the LEDs too. I had to replace ONE of those tiny zener diodes too - plus you need thermalpaste like Arctic Silver or better Arctic MX4.