Ah yes, the old Apple 341-0813 ROM, stored in a TC534200P-F749 mask ROM. Its pin layout matches the M27C400 EPROM, whose programmer profile worked for reading it. The GQ-4X’s D27C4000 / uPD27C4000 profile also produced usable reads. These were read profiles for this ROM, not programming settings for a mask ROM. Then I remembered that chip from way back when I was given some Japanese Sega Channels to dump.

The reads I trusted repeatedly produced 02FFEC64 as the checksum displayed by the GQ-4X. Selecting the AM27C400 profile instead gave a different but repeatable 0361A4B4 result, which did not match the reference ROM image. A repeatable checksum alone doesn’t make a dump good.

The good dump matched the reference image labelled A49F9914 - Classic (with XO ROMDisk).rom, and it also worked in Mini vMac. For my GQ-4X workflow, I had to byte-swap that image before writing it to a 27C400 EPROM. Quite an interesting machine with System 6.0.3 in the ROM.

Thanks to Mini vMac for allowing us to test the ROM easily, and to the ROM creators for using Gary as padding.

Sources