Hi! I have recently managed to bring my Macintosh Centris 650 back to live after it didn't want to boot anymore after replacing the PRAM battery. Just powering the Mac on with the battery removed helped to fix the issue and afterwards I could just put the battery back in and it would still work fine.
I had some issues with the SCSI bus with kernel constantly resetting the SCSI bus during boot and the CD-ROM drive showing up multiple times in MacOS. I managed to fix this by just detaching the CD-ROM drive from the SCSI bus. Since the CD-ROM drive and the HDD worked fine with the exact same setup, I just assume those are some problems with the SCSI cable used or the contacts since I had to detach the SCSI cable to disassemble the Mac to access the PRAM battery. Anyway, it works for the time being and I will probably just replace the SCSI cable at some point. As for booting Linux. The Mac boots fine with Linux 3.14 but just seems to crash when trying the most recent kernel, 3.16.0-4. I haven't done any debugging yet, but I'd guess it's either a regression in the kernel or just an issue with the kernel image itself. I haven't played so much with the Penguin boot loader yet, so I don't know what to try to debug the issue (serial port?). In any case, I guess that problem should be fixable as it can be reliably reproduced and is not some sort of Heisenbug :). As for the performance: The Mac currently has a 68040 running at 25 MHz. Reading a bit on what people from the past have to say about possibilities to improve the performance on these machines, it turns out, you can actually overclock most 68k Macs without any risk of permanent damage. The easiest way is to replace the on-board quartz crystal oscillator of 12.5 MHz with 20-MHz-type which would increase the CPU clock from 25 MHz to 40 MHz [1]. Measurements have shown that the overclocking the 68040 to 40 MHz will increase the core temperature of the CPU from around 42 C to around 47 C, thus the CPU stays rather cool. The only drawback is that the serial and parallel ports will stop working, but even this can be fixed by modifying a jumper setting on the mainboard which changes the machine ID of the Centris 650 into the one of a Quadra 650 which actually never existed [2]. Personally, I think the serial and parallel ports aren't that essential and I will just use a testclip to attach a 20 MHz quartz oscillator crystal and ignore the ports [3]. This way, I can just remove the overclock modification at any time and can restore the original configuration of the Mac without any traces of the modification. I have already ordered such a testclip from Taiwan and now I am just waiting for it to arraive. I guess the Centris 650 with a 68040@40 with 136 MB RAM and a fast IDE harddisk will make for a usable buildd machine. Adrian > [1] http://www.applefool.com/clockchipping/ > [2] http://www.applefool.com/clockchipping/c650.html > [3} http://www.applefool.com/clockchipping/mod3.html -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer - [email protected] `. `' Freie Universitaet Berlin - [email protected] `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913 -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: https://lists.debian.org/[email protected]
