Determining the age of electronic equipment by visual inspection is a useful skill. In many cases, we can read the date code directly from larger internal components such as integrated circuits and transistors. Ironically, calculating age is not as important as distinguishing what is and what is not a part number.
Let’s start by examining the AMF stopwatch shown in Figure 1, where we see two candidate part numbers including ICM7205IPG and 7638. Without understanding date codes, we are tempted to search both part numbers. That would be a mistake, as 7638 is a date code and ICM7205IPG is the true part number.
Figure 1: Circuit board for an AMF stopwatch PCB featuring the ICM7205IPG IC with a date code of 7638.
Reading the 4-number date code
The 7638 code for the ICM7205IPG IC as shown in Figure 1 is representative of the 4-number date codes. The code is read as a YYWW with 2-digit year and a 2-digit week. We conclude that the IC was manufactured in the 38th week (mid-September) of 1976.
Determining the age of the equipment
A date code such as 7638 is a single data point. We can definitively say that the stopwatch was manufactured after 7638, but we don’t know precisely when. Assuming a robust supply chain, we can speculate that the stopwatch was made within the year. The stopwatch is therefore about 47 years old.
Date codes are still used
The 4-digit date code is often found on vacuum tube as well as solid state equipment. While I don’t have an exact start date, I have seen component date codes extending back to the late 1930s.
As a general observation, the practice does not appear to be as prominent as it once was. However, it is still used as shown in Figure 2. This Microchip (Atmel) AVR32DD28 microcontroller has a date code of 2333 indicating that it was manufactured in the 33rd week of 2023.
Figure 2: Image of a new Microchip (Atmel) AVR32DD28 with a date code of 2333.
Figure 3 provides another example for the PCB of a Sinclair (Timex) ZX81 personal computer. We see many date codes:
-
8309: large silver TV modulator
-
8239: ULA 2C21 logic array
-
8342: uPD780 microcontroller (z80 compatible)
-
8304: marking on the upper left of the PCB
Based on these numbers, it’s possible that this computer could have been a 1983 Christmas gift.
Use data codes with caution
You may have noticed the 7805 code stamped on the TO-220 regulator in the lower right-hand corner of Figure 3. This is an exception where the part number looks like a date code. In this example, the NEC 7805 regulator accepts a 9 VDC power source and provides 5 VDC to the remainder of the computer. It’s possible that the 450H marking contains an embedded date code. Unfortunately, I am unable to locate the original documentation.
There are certainly other exceptions not addressed in this note. Consequently, we should always be on guard for misinterpreting the part numbers.
Figure 3: Image of a Sinclair (Timex) XZ81 microcomputer’s PCB featuring a variety of date codes.
Parting thoughts
Data codes are a convenient way to determine the age of electronic components. More importantly, knowledge of date codes helps us identify replacement components as we can quickly eliminate date codes from the search.
Best wishes,
APDahlen
Related information
Please follow these links to related and useful information:
About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.