Casper Warnich wrote: It would help to know the SadMac codes (a couple of them, anyway - though, IIRC changing numbers was usually a RAM or motherboard fault). Here are the codes for the original Mac ROMs (pulled from Google): Sad Mac Error Codes On the original ROMs (128k, 512k, 512ke, Plus): This numeric code is in two parts: the first two characters are the class code and the second four are the sub code. The class code tells what part of the diagnostic program found the error and the sub class code tells what the error was. In the case of a bad RAM chip, the sub class identifies the bad chip (this was very helpful to homegrown upgraders). Class Code: Sub Code 1 = ROM test failed, Meaningless 2 = Memory test - bus subtest: identifies bad chips 3 = Memory test - byte write: identifies bad chips 4 = Memory test - Mod3 test: identifies bad chips 5 = Memory test - address uniqueness: identifies bad chips Single Chip Identification Data Bit : Location : Sub Code Bits 0 : F5 : 0001 1 : F6 : 0002 2 : F7 : 0004 3 : F8 : 0008 4 : F9 : 0010 5 : F10 : 0020 6 : F11 : 0040 7 : F12 : 0080 8 : G5 : 0100 9 : G6 : 0200 10 : G7 : 0400 11 : G8 : 0800 12 : G9 : 1000 13 : G10 : 2000 14 : G11 : 4000 15 : G12 : 8000 Class Code : Sub Code F = Exception : 0001 Bus error F = Exception : 0002 Address error F = Exception : 0003 Illegal instruction F = Exception : 0004 Zero divide F = Exception : 0005 Check instruction F = Exception : 0006 Traps instruction F = Exception : 0007 Privilege violation F = Exception : 0008 Trace F = Exception : 0009 Line 1010 F = Exception : 000A Line 111 F = Exception : 000B Other exception F = Exception : 000C Nothing F = Exception : 000D NMI (normal indication) F = Exception : 0064 Couldn't Read System File into Memory Mike