Thanks for the suggestion, I wouldn't have thought of that - that makes a lot of sense!
I'm still trying to figure out exactly how to take Spike apart, without messing with the parts like the leg drive mechanisms that are working correctly. It is not even obvious to me, how to get the base of his internal battery compartment off - so I can replace the very short, proprietary battery connector they had with a standard RC 9.6V connector from Radio Shack.
When I was growing up, my brother and I tried to fix a Major Matt Mason Space Crawler from Mattel that had stopped shifting into drive when the winch reached the end of its rope. The thing had a top and bottom half with the crawler leg-wheels sticking out the sides. We undid the screws and gently pulled the top and bottom apart - only to have a million cogs and shafts fall out, looking like the insides of an automatic transmission. We never could re-situate or hold the internal components in place - without the manafacturing jigs they obviously had at the factory - to get the thing back together, so it worked at all. The lesson we learned was "You may be able to take it apart, but that doesn't mean you can ever get it back together correctly"!
Well, if Spike's problem is a bad soder joint (and it is interesting to note that about 30% of the people writing reviews on the Fisher-Price web site report the same problems that we see to a lesser degree), I would guess that is inside his main body - where the main power switch is. When he locks up, everything about him looses power, not just the motion, lights, or sound - so the defective joint is probably pretty central to how he is wired up. I do not think this is an over heating issue, since Spike will start hanging up immediately upon turning him on - after we'd had him for several days. My son was always very gentle playing with Spike, so aside from all the jarring his normal movement make - no reason to think we did anything to break him (and he was doing the hanging a little bit when we first got him out of the box too).
I've been wondering if Radio Shack or someone sells a fiber-optice tool that could allow me to look inside Spike through a small hole, which would also need an internal light (like two fibers)? That would be helpful for "scouting out" what is inside. I'm just afraid that if I unscrew everything to open up his main body, all the drive mechanisms and gears may fall out and I'm toast about ever getting him back together again...
New Spike still hasn't arrived yet, a week after they should have received the returned battery connector via Priority Mail. Hopefully in a few days!
Thanks again for the good thoughts! Watch this space, to see what eventually happens!