Thanks David for taking the time to go through that and give me a place to start looking. I had some time to sit down with this scope on the bench tonight after work and here's what I found.
The store signal coming in at R602 is nice and strong, 0V/5.1V, -0.3V/5V on the collector, so I don't think there's any issue there.
Checking the resistors that drive U130 and U180 all check out the same in circuit, everything looks pretty reasonable there. I was measuring in-circuit values, but nothing obviously shorted. However, following along on the schematic "vertical preamplifier. and channel switch <2>":
The output from U600D and U600E switches only between 0V/3V depending on the Ch selection switch. The inputs/outputs of the flip flop U540 and U600B/C all flip between a nice strong 0V and 5.1V. Is that right? I guess it is driving various loads including the bases of two transistors instead of other TTL ICs, so its not really "TTL" anymore past that point. The voltages read the same on both Ch1 and Ch2.
At the top around U130 there are two markings that indicate +3V on and +2.5V off. For U130, both of these values check out when flipping back and forth between channel 1 and channel 2.
At the bottom around U180, they do
not measure correctly, they flip back and forth between 2.54V / 2.57V on the top one, and 2.48/2.67V on the bottom. Not a nice strong 3V like U130. Would this be channel 2 being stuck "on" at ~2.5V all the time and bleeding over into channel 1? Seems like it certainly might be suspect. Pin 1 of U130 measures -0.59V / 0.59V and Pin 1 of U180 measures -0.57 / 0.62V, so it would appear they are being driven about the same, but the output varies between ICs.
What would you make of that? A bad U180 perhaps? A CA3102E.
After focusing in on that chip, I found this similar post here on the EEVBlog forum:
https://www.eevblog.com/forum/repair/tektronix-2225-very-weird-vertical-position-fault/I didn't realize it was an issue, but I have that same vertical position fault, looks like the labels are even the same on the 2225, U130 and U180. A new CA3102E fixed his issue, now time to find some on ebay.