Part 5: Dumping the ROM.
De-soldering surface mounted DIP chips is odd but not that hard. the problem is that I really didn't want to break any ROM pins doing so. Removed both CPU and ROM chips, and cleaned the PCB surface carefully afterwards of old solder and flux.
The CPU is replaceable (I have two 68B09E as spares for Arcade stuff), so I went fast on that.... however I especially pampered the ROM chip. Its bent pins carefully inserted in a dual wipe socket and dumped it:
The ROM had those checksums:
And contained the text seen in the boot picture.
As I always do in my research, I copy the contents of a fresh ROM dump back onto a known good EPROM, and try to see if it behaves the same if I placed it again in the device. And as expected it did.
I'm now confident the dump is good. And the sockets will allow me to move on to the next steps!
(notes the sockets are in fact two SIP's each, so that I can trace the board later)