Bill, I really hate to say this and please don't take this the wrong way, but this isn't the first time you've tested something live and something goes kaput. So I suspect that your test probes are too thick, not sharp so they slip on the joints, shaky hands, whatever. The point is that it's easy to fry something when boards are live. I recommend that you get yourself a good set of micro spring hook probes. They have small hook shaped ends that hook on and don't let go. I use them all the time in locations where I don't feel 100% comfortable that something might slip and maybe cause a small puff of smoke. I'm serious. They aren't expensive and will end up saving you tons of headaches the more you use them. Plus the good thing is that once the hooks are clipped on, it leaves you hands free.
Now as to your VZ2000, something is dragging down the voltage. You mentioned you checked IC902 and the voltage is low, but we already know that. The question is whether A the supply at the pin is low or B the IC itself is internally shorted dragging down the supply. Why you focused on IC902 I don't know, but I am guessing that anything connected to that supply rail right now is going to be showing low voltage. You need to find the source of the short or drain. There are a couple ways to do this. The simplest for you right now is to start disconnecting to isolate the problem and narrow down possibilities.
Based on your original measurements, C:Q701is showing low voltage condition with PS hooked up but normal voltage disconnected. Looking at the circuit diagram, that rail also powers 2 connectors: CNS403 to tape deck, and CNS501 to microcomputer. Disconnect one or the other and see if the voltage returns to normal. If voltage is normal with one of those connectors hooked up (and not the other), at least you've narrowed it down.
Follow this same technique to further isolate. Once you've narrowed it down to the problem board, then you are getting somewhere.