Re: 7A16A with an unknown modification MOD515D
So I confirmed that this amplifier should work normally when in the local mode. I also confirmed that this mod would only work on a 7704A with MOD 515C.
Back to the problem... In general the unit had low gain and when you use the Position control it would simultaneously adjust the gain of the applied signal higher at both extreme ranges of the control.
Solution: R705, bias resistor for the signal splitter amp, was out of spec. Was supposed to be 80.6 ohms but measured about 119 ohms. It was slightly discolored, see my photos... https://groups.io/g/TekScopes/album?id=263432
All in all good entertainment I would say.