nice job with the diagnostics. Soldering is the way to go. You don't need any more solder just touch each joint long enough to melt it for a second and then let go of it. the joints in question are the big ones on that main board underneath the cover. search the civc forum, there plenty of post on this there and somewhere there is a good DIY for the solder trick. if you get a new one make sure it is actually new. I wasted $20 for a one from a JY that had the same damn problem.