In a last, desperate attempt (or not really... but it sounds better that way), I decided to swap the igniters for the UV lightbox tubes. To be sure, I bought both single and serial versions. No need for that, the tubes lit up on the first try! I am feeling so relieved now. As soon as I get money, I'll buy the 4 missing ballasts as well as the glass plate, and the UV lightbox will be done!