The Psion Series 3mx was the last model in the Series 3 line, launched in mid 1998, and is an upgrad to the Series 3c. The main differences are: a silver metallic finish, a CR2025 backup battery, and a faster processor, the 16 bit NEC V30MX (80C86 compatible) running at 27.684 MHz. It has a backlight like the later models of the Series 3c.
Another design difference was a set of two microswitches that detected the state of the two SSD drive slot doors. These were responsible for a common fault where SSDs are not recognised because the switches fail. I discovered that this may often be due to removing the motherboard for repair with the SSD doors closed. It took me two Series 3mxs to discover this and find out how to repair it. Here's how I found and solved the mystery of the Psion Series 3mx SSD failure.