Hi Keith,
I see that you are having issues with your Microwave Oven.
You mentioned that you replaced the surface light and that something shorted out making a popping noise and some sparks but no light and the Fan does not work Either but everything still works.
I checked on the issue regarding your concern and you can download the
Manual regarding your concern at teh GE.com website or call 1-800-626-2005.
Regarding your Concern I believe that the Fuse is Blown that is the reason why the Fan is not working and so is the Bulb that you just replaced.
Replace the Fuse and check the Bulb placements to see if there are any electrical connections that are touching each other causing a short on the Microwave.
I tried checking what type Fuse it is but it does not specify, I guess you will have to get the Fuse itself to find out since it will be labeled on it.
After doing some checking I do not see anything Else that could be wrong since you mentioned that everything Else works but for the Fan and the surface Light.
I hope that this will help.
Thank you for choosing Fixya,
mvincentc