Not problem at all!!! Haven't had a problem like this in one of my machines for ages so I am enjoying the challenge and still learning myself. I actually like fixing them as much as playing em.

Since the machine has always had these issues it is possible someone has done some incorrect wiring or you are dealing with multiple problems. Both of which are the hardest to diagnose in my experience but when you find it you will wonder why you couldn't see it straight up.

For example if some has replaced a lamp holder and swapped the row and column wires the good diode will essentially act as a shorted diode but at a glance it looks good. Easy to over look small details like this when your bent over a machine with a torch.

A set fault pattern is a good thing as hopefully you can isolate parts of the matrix to narrow it down.