That old stuff you need to be there when it's broke usually. Unless you have a really good lead/ circumstances to follow and look into certain things.
Another good idea, rule something out every visit. Order a few sees replacement IBM relays and swap out a couple suspect ones every trip keeping a detailed log is a good idea. If the callback comes in again you know it wasn't the ones you just replaced. Put the old ones back then rule out the next on your suspect list.
