I had this problem, I do repairs myself, i couldn't fix, took it to 2 other repair shops they couldn't fix it either, when I got it back the final time I took it apart again, blew it out and reseated it and suddenly it just started working again and has been fine ever since. My jumper was not missing so everyone was clueless... seemed like a fluke, don't know what caused it, and not sure how many times it was taken out and put back in but I'd guess at least 6/7 times, if your jumper isn't missing I'd just keep trying! It's a horribly frustrating problem if you're not missing the jumper and know your cameras are good