Author Topic: KBT Race backlight repair  (Read 712 times)

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Offline gcj

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KBT Race backlight repair
« on: Sun, 14 July 2013, 13:26:47 »
Hey guys, been a long-time lurker but first time posting. Bought a KBT Race after positive reviews on the forum, and loved it. Unfortunately, it came with some backlight flickering issues, mostly on the F-row. I didn't use the backlight all that often, so it wasn't that big of an issue (not big enough to warrant shipping it back at least). I opened it up and couldn't find any immediate problems like blown capacitors or bad solder joints, so I just dealt with it. Now that I'm selling it, I figured it was a good time to repair it. I know some other people had problems with the backlight so I'd figure I would write up how I fixed it.

On my keyboard, F1-F9 was affected, with F9 being particularly bad in terms of flickering (and sometimes going out) at low brightness. When turning the brightness up high, the problem would disappear. My first guess was that one of the diodes was defective, since I doubted any non-semiconductor passive components would exhibit a sort of "breakdown" behavior and start working again at higher voltage/current. Indeed, after taking out the F9 LED, the problem disappeared. The diode was probably shorting open at times, which prevented any other diode wired up to the same voltage rails from receiving current and making them look defective as well. If you see one particularly bad key, and others around it starting to act worse and worse, it's probably just one bad diode wired in parallel with the LEDs around it.

I ended up putting the caps lock diode in the F9 spot, since that key is rarely lit and it won't look too funny if it has a different color. It looks like the resistors are set up for a forward voltage drop of around 3V, so I put in a 3V 3mm red LED in the caps lock key. A word of warning, the LEDs in the keyboard don't have a lip on them like most LEDs do (at least the ones from radioshack...), and are slightly shorter. I had to dremel out the lip and shorten the diode around the edges to get it to fit comfortably in the key switch.

I hope this post has given anyone trying to fix defective backlighting some guidance, since I couldn't find any information on working fixes on this forum.