I want to listen in on both directions of communication between main board and control panel of a Canon Pixma MX340 multi-function inkjet. I thought I had the hardware on hand to do this: one USB serial adapter that I've been using successfully for years, and a second adapter I bought but haven't needed until now. The second unit turned out to be a dud, wasting some of my time before I realized it was junk. I went back to my earlier purchase and ordered another unit from the same Amazon listing. (*)

Even though I ordered from the same listing, I did not expect to receive an identical unit. It's very common for Amazon vendors to switch products without switching the listing. This can be done maliciously, selling a listing with high star rating to another vendor who then offload junk. Sometimes this scam is obvious as the reviews discuss a completely different product, but some buyers don't even bother to read those reviews to pick up on the fraud. Even without fraudulent intent, a vendor may switch to shipping a different but similar product or upgrade to an updated version. I think I have the latter scenario. Here's a picture of the new arrival (top) and my veteran workhorse (bottom)

The two devices are substantially similar, with the same size, I/O locations, and number of surface-mount components laid out in the same locations. But the circuit board underneath is not identical with small differences such as the width of traces, taking turns at different angles, or small differences in printed labels.

The most visible difference upon power-up: LED colors. My veteran uses three red LEDs, the new adapter use three different colors. Yellow for power, green for receive activity, and red for transmit activity.

The product listing advertises FTDI chip. Is it a genuine FTDI chip or one of the many fakes riding on FTDI's success? I don't know how to tell. I do know, however, that this new adapter passed its first test making it better than the dud. I wired it to listen to traffic from MX340 main board to control panel. I pushed a button on the control panel to trigger a LCD screen update, and this new adapter reported 1020 bytes of data was transmitted. This was the expected value and good enough for me to get back to work.

This teardown ran far longer than I originally thought it would. Click here to rewind back to where this adventure started.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases