For a radio that first showed up around 1992, you can imagine changes in the production design every few years will leave you with a lot of possibilities.
Until March 1995, the computer and display were a pair of piggybacked circuit boards. This one has a lithium coin cell soldered to the CPU board for battery backup, and last-frequency used memory. The main circuit board will be marked "EPT295010Z"
From March 1995 until roughly Y2K, the improved display and CPU are on a single pc board. No battery. This one tends to burn up the two half-watt resistors in the display-brightness control circuit. Pretty sure the main circuit board for this is EPT295013Z. Not really sure what year the main board number changed.
The Y2K upgrade was marketed with the suffix "DX" behind the model number. The main board is totally new, mostly surface-mount parts. It will be marked "EPT6950" followed by a couple more suffix digits. The computer and display are totally different from the previous radios and will NOT interchange.
Later "DX2", "DX3" I'm not so clear on the fine differences. After 2006 or 2007 the radio's final and driver transistors changed from the bipolar 2SC2166 and 2SC1969 transistors to the IRF520 MOSFET.
This was done to allow the radio to be built lead free. A radio built since then is also built with lead-free solder.
Ugh.
Sounds like you won't know what you have until you lay eyes on it.
73
