This is going to difficult without knowing how the thing is wired, since we can't physically look at it. So, can you provide a lot more information about it?
Product numbers.
Not just the product number of the toy, but of all the components you can.
Any numbers printed anywhere: the controler, the motors.
(Hopefull one of those has been used in some other device and will show in a search engine.)
How about a photo of the wiring. I'm not sure what information we would get from that, but maybe it would help up to raise the right questions. A photo of the plate on one of the motors showing all the manufacturers info about those might help, too.
If it easy to take photos and post them to tinypic.com or facebook or somewhere then take a whole bunch. Every component (and the burnt out board from eBay.)
Also, about that board from eBay. How did you know that it would work with you model? How did you hook it up? Do you have that eBay auction id number?
I know... Lots of questions. Some may be useless, but some might help.
-tim