Side project - MV864A restoration - substantial progress in reverse engineering

POWER SUPPLY SCHEMATIC VERIFIED WITH LTSPICE SIMULATION

I had some errors in the schematic I drew for the power supply, which I identified when I began simulating the power supply in LTSpice. I had to invent a few models for the germanium transistor and RA1 reference amplifier, as well as dropping everything from the main transformer back to the wall plug, then put some resistors as loads for the -14.5VDC, -6VDC and the AC supply for the power on lamp. 

The result is a high confidence schematic for the power supply:

MAIN BOARD CAPTURED IN A SCHEMATIC

My drawing of the main board components is done but I have not yet done LTSpice simulation of the sections to validate my work or spot errors. Simulating transformers is a bit hokey in LTSpice, particularly a schematic with five independent transformers most of which have center tapped windings. Instead, I will replace the transformers with voltage/signal sources and inductors as the output load so that I can watch each section perform its role. 

DRAWING THE RANGE ATTENUATOR AND FUNCTION SELECTION CIRCUITS

The range attenuator selects the proper range for the input voltage, current or resistance, with fifteen steps or levels. It is implemented with a complex rotary switch having eleven sections with fifteen contacts apiece. This switches resistors to reduce the input to a standard level that the rest of the circuit is designed to handle. 

The function selection circuit has six positions - off, + voltage, - voltage, +current, =current and ohms. This rotary switch has seven sections with six positions each. I am about halfway through the range attenuator capture at this point. 

WILL CAPTURE INTERCONNECTS BETWEEN BOARDS AND CONTROLS

There are quite a few wires that run from the rotary switch to the two PCBs - as the power supply PCB has many of the resistors on it that are part of the range attenuator, it has the most wires connected. There are also a number that run from the input jacks and the main PCB to the range attenuator. That will wrap up the work reverse engineering this meter.