Rebuilding and Testing a Marantz 2385

I got this 2385 in a trade. It was in rough shape and not functional. The specific-to-this-model volume knob and shaft was missing as were many of the screws holding it together

Here are a couple of pics after cleaning it up before restoration:

Restoration

I started with replacing all of the burned out lamps with LEDs. The function panel was already LEDs and working, so I left that alone

I then restored the following boards:

P400 - Phono & Selector
P700 - Main Amp
P850 - Power Supply
PE00 - Pre, Tone Amp
PN00 - Audio Muting Circuit
PQ00 - Soft Start Circuit
PS00 - Switches Board
PT00 - Filter Amp Circuit

This restoration consisted of replacing all electrolytic caps with modern Nichicon, Panasonic, or Kemet equivalents, replacing all known problem transistors with modern equivalents, and replacing the filter caps with 4 10k modern caps.

The filter caps required designing and 3d printing a new capacitor caddy to handle the difference and can be found here: Thingiverse - Marantz Filter Adapters

The volume knob and shaft was also missing. Originally, I designed and 3d printed a replacement knob that would go into the existing hole and engage the potentiometer mechanism. After proving the concept, I purchased 5mm stainless steel rod from amazon and ground it down with a cutoff wheel to fit what I 3d printed.

Testing:

Since the Marantz 2385 has pre-out and amp-in connections, I tested the amp separate from the preamp+amp to compare the performance of the amp versus the preamp