I find it interesting to see what things look like inside and how they were put together. This was not designed to be taken apart but a little persuasion and a little cracked plastic took care of that over site.
Not a lot to the circuit but when you lose the power lead it doesn't work well. The arrow points to where the lead needed to get put back on.
So if you have never seen the insides here you go:
Had the soldering station out anyway for my optical tachometer repair so figure might as well do this job as well.