I purchased a non-working Motorola R2210B/HS service monitor just to take a look and see if it was repairable. Part 1 of the video is the teardown of the basic unit and troubleshooting the LVPS section.
I put this together for testing. Package download is below (At Very BOTTOM). You will need to homebrew a non-standard ngspice (doesn’t have ngspice lib by default). Its avail here https://raw.githubusercontent.com/jmaibaum/homebrew-core/8ac02ae933c4cd5d1f661b6a2bda2f429d5f1e87/Formula/ngspice.rb . Note the NGSpice homebrew is in flux and this version is done jmaibaum.