---snip--- Hi Once many years ago while working for Intel, I was called in to help fix a number of what we used to call yellow dot boards ( failed but not repaired after third rework and had a yellow dot placed on them ). The yellow dot inventory had a sudden jump so someone needed some additional help. The boards had a lot of analog circuits on them because they had a discrete component PLL used for the disk controller. I had the fellow from system test with me to take notes on how to diagnose complicated failures on these boards. As it turned out, about 90% were caused by a mix up in the parts loaded on the boards. A low voltage zener was placed in a number of locations that expected signal diodes. This especially effected the balanced mixer used in the phase detector. After some time of carefully showing the system test fellow a number of scope signals and carefully explaining the reasons I was looking at particular locations, I happened to glance at his notes. It went something like this: D3, D5, D8, D20, D21 There were no symptoms and nothing of what I showed him about scope information. I soon realized that he was just interested in a list of parts that I indicated as causing problems and wasn't even paying attention to anything else I was doing. The worst part was that since this was a one time parts mix up, it probably would never happen again so that his list was virtually worthless. I told him this but that didn't seem to ring a bell with him. Dwight