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Saturday, September 7, 2019

From clumsy feet to surgeons hands!

Posted: 3:00pm

I have lots of wires everywhere in my work area, and I have big clumsy feet especially with the rubber Crocs I wear all the time.

Today I caught the USB cable going to the Switch Module that was sitting on my rolling worktop, yanking it off onto the floor with enough force that it broke the solder connections on the USB connector.  The Mega is screwed to a piece of wood which also contains other parts for the Switch Module, and is somewhat hefty.

These are TINY!!!

You can see them highlighted in yellow.  If you wriggle the cable, the module flickers on and off, making it pretty well useless.  Using my big magnifying lamp, and a smaller magnifying glass (it's that tiny!) I was able to see the little tabs lifting off the main board when I wriggled the cable. So faced with having to replace the whole thing, I grabbed my thinnest soldering tip, and figured I couldn't make it much worse (in retrospect, I suppose I could have) and while holding the USB cable so that the tabs all made contact, I touched them with a hot soldering iron. I didn't add more solder, since I knew cleaning it up after would have been risky...  Once I gave each a little reheat, I plugged it in and it works! So from clumsy feet, to surgeons hands!

Update: September 08, 2019  6:40am

That didn't hold very long unfortunately.  Because I'\m actually working on the Switch Module, I occasionally need to unplug and plug the USB cable in, and physically pick up and move the whole thing, the flex on the cable was more than my fix could handle. I only heated the solder joints, I didn't add any more solder. 

This morning I did add solder, a big blob that covered all the little tabs.  There is no way to get solder on to each individual tab by hand, so the technique I'm aware of is to melt a big blob on the whole area, then lift off the extra using solder wick. Solder wick is just braided copper, and when you lay it over excess solder, and heat it with the iron, it will wick up all that solder, just leaving the solder actually making the connections.  This was my first attempt at an actual rescue job using this technique.  I ended up scraping a tiny bridge off with my xacto knife, but when I plugged it in, it worked and didn't short out my USB port :)

I ended up adding a soft rubber pad under the actual USB cable where it connects, and taping it in place to create a more rigid, rugged connection. The USB cable is almost permanently connected now, in fact, I was thinking of epoxying it in place!   I'll just order some spare boards, they are less than $15 each.

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