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[AlexTheCat123]

Someone just listed a Lisa on eBay with a ROM switcher installed that lets you change between H and 3A ROMs (as well as the MacWorks screen mod) with the flip of a switch. I've heard about these switchers, but I've never actually seen pictures of one, so I figured I'd post this here in case anyone else wants to take a look!

[Lisa2]

There is more RomSwitcher info on bitsavers:

http://www.bitsavers.org/pdf/apple/lisa/macintosh_xl/

[AlexTheCat123]

Good to know! I had no idea that there was anything on Bitsavers about these things.

[Lisa2]

For completeness on this subject, the Sapient CPU recreation has among it's many enhancements has a built-in ROM Switcher. Using 256K EPROMS and a special VideoProm that supports four Lisa ROM sets (versions H,D, C, and 3A ).  The ROMs are selected using some switches on the board but these switches can routed externally also.  A photo of this board is attached, (please ignore the XLerator in the photo)

I made a very rough video of the operation here:
https://youtu.be/56KtI2uQaWg

Note: if switching between the older (H, D, C) and screen mod ROMs (3A) the screen pots really need to be adjusted. The original ROM switcher instructions recommend a compromise of settings between the two setups.   Neither the original ROM switcher nor the Sapient board switch in the yoke transformer for the screen mod. 
Rick