I am getting 50v but not sure where to measure the 80v to be that they are being summed correctly.
The 130V supply is divided by R855 and R856 in a 2.6:1 ratio to produce exactly 50 volts at the junction of the two resistors. Q852 then compares that with the fixed 50V output of the 50V supply, and if the two do not match then buffer Q850 raises or lowers the voltage applied to the bottom of the "130V" bulk supply (which is actually more like 90V if measured across its filter cap, C806.)
When all is operating normally, Q852 holds the bottom of the "130V" bulk supply at about 40V, so that the top of that supply sits at 130 volts after the addition of the 90 volts from the bulk supply. If the voltage at the base of comparator Q852 is too high, then Q850 turns off a bit to lower the voltage at the bottom of the bulk suppy. It the comparator voltage is too low, the opposite happens. Thus, the output of the 130V supply is regulated at exactly 130V.
If you are seeing too much voltage out of the 130V regulator, it may be that something in the Q852/Q850 chain has failed. If Q850 has shorted, for example, then the bottom of the bulk supply will go from its nominal 40V to a fixed 50V, causing the total output rise 10 volts and become about 140V. Other faults could cause similar misbehavior, so some investigation will be needed.
Check the schematic at W140.com for reference, btw.
https://w140.com/tekwiki/images/b/b4/Tek_7603_power_supply_A10_and_A11_schematic_%28redrawn%29.pdf Good luck.