Heathkit IM-4100 Frequency Counter: History, Overview, Demonstration, Theory

In this video, I document the Heathkit model IM-4100 frequency counter. I normally do documentary videos on older equipment, but decided to do this one while I had opened it up for troubleshooting (unnecessary, as it turned out), because it is one of only three items of Heathkit test equipment which I built myself and still own and use. I built it around 1978 while in college, and it has been on my electronics workbench until recently, when I relocated it 'display-only status' on a large wall-shelving area along with much of the other vintage Heathkits.

Table of Contents Timeline:

00:00 Introduction & History
03:46 About this unit
07:16 Repairs
09:47 Test & Demonstration
22:11 Repairs, continued
23:11 Beauty shot
23:31 External tour
34:26 Internal tour
54:42 Heathkit manual overview
1:02:44 Schematic diagram & theory of operation