[JGlass] deals with public-facing technology, which he says includes things like theatre equipment, retail displays, and museum displays. Many of these pieces of technology are literally one-of-a-kind devices, even if they were constructed from what was once off-the-shelf, commercially available parts. When these machines need servicing, replacement parts aren’t always available, and reverse engineering comes in handy. He recently began documenting exactly how to approach this process by using the identification and replacement of an obsolete 7-segment industrial display as an example.
The particular part shown is the Lascar EM32-4-LED, which up and died in a unique piece of equipment. The trouble is that the EM32-4-LED is out of production and unobtainable, and the Programmable Logic Controller (PLC) that drives the whole thing is a black box that cannot be modified. It’s very good news that a datasheet exists, but that’s often just a starting point. To create a one-off, drop-in solution requires a combination of research, troubleshooting, and design work.
To do this, [JGlass] starts off by walking through datasheet elements and explains that it’s important to build a high level understanding of function first, then drill down into details, and always be ready to verify, challenge, or throw out one’s assumptions. After establishing a high level understanding comes matching physical evidence to things like block and functional diagrams, then cracking open the faulty component to see if anything else can be learned. Only then are multimeters and probes taken out for more active research. All of this sleuthing must always be done with the end goal firmly in mind: creating a new device that acts like the one being replaced. Without focus, one can easily get lost in details and unknowns.
Reverse Engineering is a process, and the more tools, the better. If you missed our earlier post about a hacker’s guide to JTAG, here’s your chance to check it out and be all the more prepared for the next time you need to do some electron detective work of your own.