Ray Carlsen discovered an EPROM in a C128 he had been repairing. Here is his comments in quotes (my questions are marked with 'more than' symbols) --
"I got a flat 128 in for repair and it had an EPROM in U36 that didn't show anything at boot. Some investigation shows it to be a collection of utilities with the name Jay Schollmeyer and a date of 1988. It's a 27512 (64K EPROM) with a switch to select two 32K banks of code. Some parts of it will run in 80 column mode and most in 40 column. One of the 80 column programs is Super 8 utilities copyrighted Free Spirit Software. There is a terminal program, disk and file copiers, disk editor, NIBcopy, etc. I figured out how to run some of it but other parts are obscure."
(snip) > If so, how did you activate the EPROM?
"The 128 showed a normal boot screen. Some functions were accessed with the F keys and one by holding down the control key at boot. There may be other functions but these I found only by fumbling around with it."
> It's a 27512 (64K EPROM) with a switch to select two 32K banks of code.
> Like a SPST switch?
"Yes, same as a JiffyDOS double-EPROM select."
Ray gave the EPROM to me; it has a resistor between 2 pins of the EPROM which is connected to the SPST switch. Ray kindly provided the BIN code which I am attaching. UTIL.BIN (64 KB)
For easier manipulation with emulators, I split the ROM in two 32768 byte pieces and managed to get output from one of the pieces by tapping on function keys. The split rom files are included in the attachment below.