more 11/45 fun

I was letting the 11/45 instruction excerciser run in a loop just to work the machine while I was digging through the RL02 prints to find all the signals going to the fault lite. Looked over at the machine and it had locked up after running fine for about 5 hours. Wonderful. I figured one of my cpu boards was probably marginal and was preparing to swap boards and then I could swear I heard Tony yelling at me from across the pond. So I got out the scope and started checking the backplane power testpoints. Sure enough, E16B2 and E21B2 are both (basically) zero, and they were NOT that way before when I had a problem with the top 742 supply. Looking through the prints shows they should have been at -15v and come from the bottom 742 built in regulator. ARGH! So now it's the same board in the bottom supply that failed in the top supply a week or two ago. Glad I ordered some extra parts from mouser when the last one died. Further thought and I realized that slots 16 and 21 are for the mos/bipolar memory controllers. I don't have mos/bipolar memory. So I was wondering what else comes off that regulator board on the bottom 742. From recent memory I believe I recall the LTC comes from there. But LTC being fried wouldn't cause the cpu to fail to come up would it? And since I'm not actually using mos/bipolar I'm left wondering what else is coming off that board. AC lo or DC lo signal perhaps? I seem to remember that something odd was done to the regulator board in that lower 742 to make the output -15v instead of 15v like the top 742. In any case, I obviously SHOULD fix the regulator in the bottom 742 so I get that -15v back but I am left curious as to if that is what is causing the cpu to suddenly no longer come up and run. Am I on the right track here? Jay