[WME_bill]

To clarify what you have found.
1. +105V rail fails. This will pull down the -24v rail. The -24V rail sets the +24V and +105V, so they also will also be low.
2. Does the effect occur with both the X and Y amp plug in modules removed. Undo one bolt for each to pull out. I suggest keep them out at this stage. It removes much of the load as well.
3. Removing +105V rail to PC128, the Beam blanking board, restores all rails.
4. So it seems that the fault lies on PC128.
I always look first at the transistors operating at high voltage around Beam Blanking PC128 and the EHT oscillator PC148.
Commercial alternatives I have used for the selected transistors on these boards : TO203 = MPS2907A / FRB749 / SPS5286 = BF305, 2N1990 / E1530LL =BF259,2N2219A.
5. I don't understand your term "sleeving". Does it mean you disconnect that wire.
6. The earth/ground return from most of the PC boards is by the fixing screws. I read it that you have measured voltages with the PC board floating about, so you may have entirely false readings.
7. It does no harm and makes it much more comfortable when poking about to remove the EHT voltages, so disable the EHT oscillator by removing the fuse FS402 on PC149. That also removes the loading on the +30v rail.
8. To test each section, disconnect each part of the circuit loading +105v rail from the PCB connection points on the lower side of the main mother board PC147. It is fiddly. Identify the wires coming from junction points 16,17,18, which go to Astig control, Trace rotate, EHT osc.
9. On the upper side of the main board, PC147, find points 9 (to trace rotate pot), 10,11 (to CRT base), 24 (to Intensity control), 22 (trace locate), 8 (twist coil).
This is even more fiddly to inspect, so look at the resistors (R631/632 etc) on the board around those connections and see if they look sound and are not hot.
The wires for these connections do not always go to the terminal point shown on the circuit, but to one of the other similar. The circuit diagrams are very confusing for the trace rotate & beam find parts of the circuit, appear spread onto several of the circuit sheets.
10. The other common fault on this family of Telequipment scopes, D75, D83, DM63, is the resistors in the EHT chains across the tube -R324/325/318/322. They are over-stressed by the voltage, and go high. Happily you do not have that trouble.
I like this scope. It is relatively light, and easy to get at and service. Well worth getting going again.
wme_bill m0wpn