Even before attempting to reverse engineer all the code (I still have to trace the CPU board; I've been pretty busy recently and motivation's been kinda low), I knew that things would be a lot harder if I can't find out anything about the mystery suspected-to-be-modems chips.

Since I have a number of them (I have a lot more CPU boards and main boards than line interfaces), I tried decapping the chips, in the remote hope to find some more information one the die (like a non application specific part number).

I used the hot air method to extract the die, which basically consists in heating the plastic packages with a high temperature heat gun until they become soft and then breaking them with pliers. As strange as it sounds, it works (see (13) Chips a la Antoine: an IC chip de-capping recipe without chemicals - YouTube for an example)

Here's the a picture of the decapped chips:

(PLCC package SCL1054-V4 on top, "wide" DIP package Italtel v7308 on the bottom)

Unfortunately, I found out that I do not have a good enough microscope to really analyze these, but I managed to find something interesting inside the SCL1054-V4

An RCA logo and part number! Unfortunately, this also brings up no results. I guess I'll have to resort to analyze the software to understand what these chips do and why.

This is as far as I've gotten for now. I really need to trace the remaining boards and to start working on the software. I do know a bit of 6502 assembly, but I've never really done much assembly programming before, let alone reverse engineering on already written code, so this is probably going to take a while. Also, as said before, I'm missing some info on the internal wiring (mainly about the electromechanical actuators and sensors wiring) so I'm a bit stuck on that front.