Macintosh Plus ROM orientation

[CharlieFrown]

Hi, 

forgot to take a picture of Hi and Lo ROMs before taking them out and cleaning them. How can I distinguish them? One of them is marked "C", the other one "B". Simple logics suggest that C is probably Hi and B is low, but wanted to make sure. 

Besides what are the symptoms of boot attempt without ROMs at all? Sounds stupid, but is it normal I get just horizontal bars?

 

[Godzil]

You can find which one is by using the part number written on the chip

 

[bigmessowires]

With the board oriented so that all the ports are at top, the HI ROM is at left and the LO ROM is at right. I think it's also labeled on the logic board.



Horizontal bars or similar weirdness sounds about right if you have them accidentally swapped.

I don't think B / C indicates HI / LO, but rather a version number. The HI / LO is the middle digits of the part number, if I recall, like 342-0341-C / 342-0342-C.

 

[CharlieFrown]

bigmess: thanks, that was helpful