Flyback Transformers - Durability

Are flyback transformers durable or do they tend to "break" easily? Reason i ask is i have been working on some hv projects, small time stuff and for the life of me i can't get consistant results.

I reference the tesla coil single transistor schematic and one day i will have the high pitch noise that is an indicator of success and all is well. When I try it again the next day nothing. No noise nothing. i check my connections so many times it makes me sick.! i usually point the finger at something i have done wrong but i don't think that is the case.

are they known for being fickle? i have gone through at least 3 of them which is really making me annoyed.

can anyone shed some light on this.. please? links comments.. anything.

by the way i really appreciate all the knowledge around this joint... some of you are out of control hardcore i love it gg.

LOPTX's are designed for one specific purpose, and even at that they tend to be unreliable (depending on their quality of construction).

Abusing then for a completely different use is likely to kill them pretty quickly.