this documents a repair of a cyton board. the board would turn on and kind of work but one couldn't upload new firmware to it.
i localised the issue to the RFD22301 (aka RFDuino) module. i desoldered it from the board using some rose's metal - a material with low melting temperature (94°c) - and then put on new temporary pins to a few pads and put it on a breadboard.
the module sort of worked but it still wouldn't be programmed. after lifting the metal can and checking the all the connections, i found a broken trace from the chip out to the rf_rxd pad (gpio0/aref) on the module. tracing the fault a bit further it turned out to be a broken via. i tried to refill the via with solder but it was just too small to repair. so i ended up adding a thin copper wire directly from the pin to the pad and wrapped it in some kapton tape for isolation.
i had to cut out a slot in the metal can so that my wire could get out without getting squeezed and shorting to ground. it doesn't look pretty, but the module now worked and i could finally upload new firmware. and after soldering the can back and putting back the module, the cyton board worked again.
i also repaired a broken trace on one of the serial lines. it's visible on the right hand side in the photo.