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Macintosh Plus - error 01204E
Posted by: drg on 2023-02-02 20:29:47 Hi, I got Macintosh Plus with broken floppy disk (currently it's disconnected). Unfortunately after powering on I got 01204E error. The keyboard is not connected (I should have tomorrow one). I tried to boot from BlueSCSI, but still the same error occurred (Macintosh SE FDHD and Classic booted from BlueSCSI just fine). Can somebody drop mi a hint? Best regards, Pawel
Posted by: bibilit on 2023-02-02 22:58:34 01 Bus Error The computer tried to access memory that doesn't exist. Do not buy extra RAM to solve this problem. Computers always try to use more RAM than they have, just like users always want to store 40 GB of data on a 20 GB disk. You can get this error on almost any Macintosh. If one of these computers tried to access one or more bytes beyond the total number of bytes in RAM, you see a bus error. You should never see this error on a Macintosh Plus or SE, because address references that are out of bounds "roll over". This means if one of these computers tries to access one byte beyond the total bytes in RAM, it actually accesses the first byte in memory. If you see this error on a Macintosh Plus or SE, it's reporting the wrong error or having hardware problems.
Posted by: drg on 2023-02-02 23:04:35 In the other hand, here http://myoldmac.net/FAQ/SADerror-earlymac.htm I see, that 01 is ROM test failed. I ordered EPROM chips and will write new ROM on them and try again.
Posted by: rollmastr on 2023-02-02 23:33:49 Reminds me of my Mac Plus that displayed 01002C. New ROMs fixed it.
Posted by: drg on 2023-02-05 20:37:33 Success! That was it. I ordered two of W27C512-45Z, unfortunately one of them had broken leg. However I dumped two original ROMs and then downloaded 3 version of ROMs for Macintosh Plus. Next I split those ROMs into HI and LO parts and then I calculated MD5 sums for all halves. As I suspected, one original ROM (actually half of ROM) matched to one version of downloaded ROM (the newest one). The second halves had other MD5 sums, so I knew which half I had to program and replace (of course, if I had 2 working W27C512-45Zs I wouldn't be doing these comparison and just burn the newest rom to new chips). After replacing mismatched half of the ROM, the Macintosh Plus came to life. The next step is to make keyboard cable. Unfortunately, at first I connected normal RJ9/RJ10 telephone cable which is not crossed, so +5v from the computer went to GND on keyboard side and vice versa. I hope it didn't kill the keyboard, I will make the proper cable this week, probably.
Posted by: Fred1212 on 2023-02-05 23:04:53 Nice work
Posted by: rollmastr on 2023-02-06 00:16:46 Congrats! Apparently corrupt ROMs aren't that uncommon on these machines.
Posted by: bibilit on 2023-02-06 00:40:34 The next step is to make keyboard cable. Unfortunately, at first I connected normal RJ9/RJ10 telephone cable which is not crossed, so +5v from the computer went to GND on keyboard side and vice versa. I hope it didn't kill the keyboard, I will make the proper cable this week, probably Doesn't kill anything IIRC
Posted by: drg on 2023-02-08 05:55:35 Indeed, the keyboard is still alive! I couldn't find my crimping tool, so I quickly prepared cross over cable from the straight one and it worked!
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