Uploaded May 2026 | Updated September 2026, 1 week ago
In this video, I document a piece of late 1970's sports-related electronic equipment, namely the "TotalTimer" digital stopwatch that was apparently made under various brand names by a California company "Cronus". This is a basic implementation based around the Intersil ICM 7205 (ICM7205) monolithic LSI stopwatch IC, also dating from the late '70s. The IC is capable of three modes of operation, "sequential", "split" and "Taylor"; the latter two modes are NOT implemented in the TotalTimer product shown.
I show some of the hurdles I needed to jump through to get my example working again. I describe the pinout and functionality of the IC, go over the schematic diagram, show an article from a British electronics magazine about how to make a stopwatch using the same IC. I relate how is diagnosed a faulty dome switch and determined how to replace it using modern parts.
Timeline Table of Contents:
00:00 Introduction
00:36 As received from eBay
02:38 Internal views, including printed circuit board
04:22 Initial tests, discovery of corroded/failed dome switch
08:08 Intersil ICM 7205 stopwatch IC
21:57 Schematic diagram
25:35 Dating the timer product and the IC
28:56 More on the Split/Taylor modes (not implemented)
32:39 Further restoration, new dome switch
36:54 Demonstration
37:57 Beauty shot
In this video, I document a piece of late 1970's sports-related electronic equipment, namely the "TotalTimer" digital stopwatch that was apparently made under various brand names by a California company "Cronus". This is a basic implementation based around the Intersil ICM 7205 (ICM7205) monolithic LSI stopwatch IC, also dating from the late '70s. The IC is capable of three modes of operation, "sequential", "split" and "Taylor"; the latter two modes are NOT implemented in the TotalTimer product shown.
I show some of the hurdles I needed to jump through to get my example working again. I describe the pinout and functionality of the IC, go over the schematic diagram, show an article from a British electronics magazine about how to make a stopwatch using the same IC. I relate how is diagnosed a faulty dome switch and determined how to replace it using modern parts.
Timeline Table of Contents:
00:00 Introduction
00:36 As received from eBay
02:38 Internal views, including printed circuit board
04:22 Initial tests, discovery of corroded/failed dome switch
08:08 Intersil ICM 7205 stopwatch IC
21:57 Schematic diagram
25:35 Dating the timer product and the IC
28:56 More on the Split/Taylor modes (not implemented)
32:39 Further restoration, new dome switch
36:54 Demonstration
37:57 Beauty shot
