I haven't been following this thread closely, but since you are now looking at the 100 MHz reference, I vaguely recall long ago having to fix it in a 8566B. The main reason it's kind of memorable, is that it was an unusual failure - a regular old ceramic cap in the PLL loop filter had gone leaky or maybe even shorted. I've seen very few ceramic cap failures over all my years, especially where they were not stressed as in HV or bypassing applications. In this one, it was just part of the filtering of the oscillator control voltage - a very low stress occupation.
Ed
