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geekhack Community => Keyboards => Topic started by: jas0835 on Thu, 23 July 2020, 21:55:33
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So I just got my KBD75 and the LED chip was stripped off and took the PCB traces with it. I took out the traces and need some help figuring out how to re-solder a replacement led. Anyone familiar with PCBs know what needs to be connected to where? I've included a picture of the back of the PCB with the missing LED as well as the PCB wiring diagram provided by KBDfans. Any help would be appreciated!
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Your pic was lost.
Make sure everything else works before even starting with the LED, it may have damaged switch traces and more.
May want to talk to them before you even attempt to mess with this.
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All the switches work and all the other LEDs light up. I thought it may have been as easy as trying to solder it back, but I think the copper pads came off, so no luck. But yeah, I've emailed them and waiting for a reply. Just trying to figure out if this is something I can fix myself. Thanks for the reply
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Looks like it trashed the pads but is relatively easy to fix.
There's a pos and neg, and a signal wire. One side of the led is pos (top I think), one side is neg (so you can daisy chain them), the signal is the middle pin.
Neg can come from almost anywhere, the USB connector if necessary.
Pos, you need it to run through the resistor, but it too can come from almost anywhere, the led is controlled by the signal and is always hot.
The last wire (signal) is serial wired, it needs to be continuous as that is how they get their order and numbering (and makes daisy chaining easier). If one fails they all move down a number, if you add one they go up a number. This makes it easy for doing racing and waves and such. This appears to be the last one in the chain and simply one before it, follow the blue line to the last led center pin. Not bad really.
To attach the LED, this is actually where it gets the most tricky...
They use the pcb as a heatsink or they will overheat. Old school trick here, put a dab of (non conductive) heat sink grease in the middle, then use hot glue (needs to be of higher temp variety) or super glue (CA) to hold it down. There is heat sink glue as well that you could use, but this will work as well or better and is easier to get.
I'd still talk to KBDfans first and see what they say.
Good luck.