Re: Reversing screen mod

Peter wrote:
> Just a quick question that I can't find the answer to in the FAQ or
> archives -- how practical is it to 'reverse' the square pixel screen
> mod on later Lisa 2/Mac XL machines? I presume you would need to
> remove the transformer, as well as swap out a few chips?
Exactly that.

> And that the
> original chips, if not saved by the owner, would be impossible to
> find?
>
You'd need to replace three ROMs on the CPU board. The VSROM plus the high/low ROM.
I'd try Vintage Micros for these. John does usually have these in stock. Otherwise if you've got the right EPROMs and burner, you could try burning them yourself.

You'll want the H ROM as that was the latest one.

Note that the VSROM also contains the serial number of the machine, so if you've got anything that's keyed to that serial number, it will likely not work.
However, since you've got the A8 ROM at this point, I highly doubt that anything under MacWorks or System 6 will care about the serial number, plus it's likely that the VSROMs for the modified Lisas aren't unique anyway.

You don't actually need the transformer to use the screen modification ROMs by the way, one of my Lisas is very happy to work with either the A8 or H ROMs. I did have to adjust the pots on the analog board until the image was the right shape, but it worked just fine. Perhaps, not optimally, but it did work.

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