oPossum, Thank you for your post.
The schematics I posted are for the P4400.
The schematics include all of the populated parts in this model, none are omitted, except the AC connectors are not explicitly shown.
LTSpiceIV was used for the analog schematic. LT semiconductors were substituted in order to run the simulation. Therefore, I omitted the semiconductor part numbers from the printout.
The AC input is shown as a sine source and a noise source. The load components are labeled DUT, again, for the sake of simulation.
The schematic is organized to render the sense of the circuit at a glance, and it is also organized for easy troubleshooting, which was my motive.
By the way, in troubleshooting, all of the signals looked normal. The unit had lost its calibration somehow, apparently from a noisy load. I have also posted the steps used to re-calibrate it.
oPossum, in your schematics, do the reference designators match your boards? I ask, because your designators are different from mine, and mine do match my boards.
I also have photos of the boards that I used for tracing the schematics (not posted).