Q605 (LC475, P475, P476) Speedup w/Apple's PPC card

This is a modification that can be performed on a Quadra 605, LC475, Performa 475, or Performa 476) outfitted with an Apple PPC card or the Daystar PowerCard 601 to speed it up to 66MHz. The card is also made for the 630's, so the card itself is not being run over specifications when it is run at 66MHz.

Keep in mind that this will void your warranty. Dealers, Apple or Daystar may refuse to accept the boards while in or out of warranty with this modification.

Take a look at Alexander W. Chin's (alex@gerulf.acsu.unsw.edu.au) Q605 (LC475, P475, P476) Speedup before you proceed.

The modification must be done in this exact order:

  1. Install your PPC card following Apple's instructions
  2. Boot the computer
  3. Install 7.5 from the provided disks. *Do Not* do a machine specific install
  4. Shutdown the computer
  5. Remove the jumper from J18
  6. Boot the computer
  7. Turn on the PPC card from the control panel
  8. Shutdown the computer
  9. Boot the computer
  10. Check to be sure it is in PPC mode (About This Macintosh... in the Apple Menu Items will say Power Macintosh)
  11. Shutdown the computer
  12. Perform Alexander W. Chin's Q605 (LC475, P475, P476) Speedup to 33Mhz

There are some Speedometer 4.0 Files for a Q605 w/Apple's PPC card at 50 and 66MHz on the Clock Chipping Home Page you may want to check out.

A few interesting tidbits:

  • If the PPC card is installed, the computer will not work at 20/40MHz in either 68040 or PPC mode if J18 is installed or not.
  • If the PPC card is installed, the computer will work fine in 68040 mode at 33MHz if J18 is installed or not.
  • If the PPC card is installed, and J18 is installed, the computer will not work in PPC mode at 66MHz; it will not start.
  • If you are running the machine in PPC mode at 66MHz and switch to 33MHz 68040 mode you will not be able to switch back; it does not recognize the card; it will say:
    The Control Panel "601 Processor Upgrade" cannot be used with this Macintosh.
    If you do this, you will need to undo the modification, drop back down to 25/50MHz, switch to PPC mode, and redo the modification to 66MHz. i.e. If you do the modification, do not switch back to 68040 mode.
  • This may be a very good case for a switch to toggle the resistors between 25/50 and 33/66MHz.

    The gestalts are as follows:

    Speed J18 Installed J18 Removed
    50MHz 104 104

    There are a few unresolved questions:

  • Where does the info about PPC vs 68040 mode reside? PRAM? Disk? (since it might be PRAM, do not zap the pram while in PPC mode at 66MHz until we figure this out)
  • I know there is software to copy the contents of PRAM; can it also write it back? Can this be done? i.e. store PPC PRAM info, and reload it when you want to switch back to PPC mode from 68040 mode.
  • Maybe the 20/40 and 33/66MHz gestalts can be added to the PPC control panel to avoid these problems.

    Any information on how to get around these problems will be greatly appreciated, and Apple employees or other contributors who prefer to remain anonymous will be kept so. :)