JFJ: Thank you again. Those voltages are similar to what I saw, but don't make sense to me. I don't see how those voltages will give me -2.6v out of the pass transistor (which inputs -4.65v).
If I traced the circuit correctly (easy to miss things with bad vias, however) it seems like a typical op-amp driving a PNP transistor (two, actually, Q151 and Q153). The non-inverting input is tied to ground, and the inverting input was tied via 1K resistor to the pass transistor emitter (i.e. output voltage) to provide feedback, but was also connected through about a 10K resistor to the +4.30v zener voltage reference (U155). (That reference is also fed to the dual op-amp driving the pass transistors for the two positive rails.)
Typically, I thought a reference voltage was applied to (In+), and a feedback sample to (In-). I'm struggling to understand this different situation, but then I haven't looked at a negative regulator before.
Does this make sense? I'm guessing that the VRef reference voltage is fed to (In-) instead of (In+) because it's a positive voltage and we want to use it to set a negative rail, so it needs inverting. And the feedback from the transistor output has to also come to that same (In-) input, so the two are sort of summed. Since (In+) is hard-wired to 0v, the op amp would try to bring (In-) to near zero as well, which means the output voltage, via feedback, would have to cancel out VRef. So it seems like that should force the output voltage to around -4.3v (which is what I was seeing on my board).
I tried that circuit on a breadboard, juggled resistor values, and got transistor output voltages no closer to -2.6v than -3.2v. But I was able to get -2.6v out of the pass transistor if I changed the circuit a bit: I disconnected the +4.3v reference from (In-), lifted (In+) off ground and put -2.6v on (In+) as a reference. Doing that seems to give a nice, stable -2.6v output with decent regulation. Unless I can understand the problem with the original circuit, I think I'll go with this modification (with the addition of a 2.6v zener to provide the reference voltage).