I just wanted to show how I've upgraded the ROMs on a regular PowerBook 520 CPU card with a couple of 29F1610 chips, programmed with the 550c ROM.
Now, why would you want to do this? Well, you might have acquired a 550c that's been upgraded with a PPC chip, but wish to revert it to its stock configuration. However, you can't just install a common 520/540 CPU card, it won't work. Genuine 550c '040 cards are basically unobtainable.
The 29F1610 chips are the correct specification and almost fully pin compatible with the mask ROMs they replace, but differ in that they have a couple of programming pins (#1 and #44) where the mask ROM's are NC. A single bodge wire is needed over each chip to pull pin 1 (WE#) high.
This particular card now just needs a full 040 swapped in, and it'll be functionally equivalent to an original 550c card. The good thing is that it'll still work in a 520/540.
I'm attaching high and low split binaries to make it easier for anyone who wants to try this, since splitting the ROM correctly was a... splitting headache. 29F1610 are out of production but plenty of NOS chips can still be found, just beware of fakes.
Here's how Tattletech reports the ROM before and after the upgrade. The sub-version changes from $30F1 to $30F2, so it's essentially Rev A. vs Rev B.
A couple of declaration ROMs are updated.
Now, why would you want to do this? Well, you might have acquired a 550c that's been upgraded with a PPC chip, but wish to revert it to its stock configuration. However, you can't just install a common 520/540 CPU card, it won't work. Genuine 550c '040 cards are basically unobtainable.
The 29F1610 chips are the correct specification and almost fully pin compatible with the mask ROMs they replace, but differ in that they have a couple of programming pins (#1 and #44) where the mask ROM's are NC. A single bodge wire is needed over each chip to pull pin 1 (WE#) high.
This particular card now just needs a full 040 swapped in, and it'll be functionally equivalent to an original 550c card. The good thing is that it'll still work in a 520/540.
I'm attaching high and low split binaries to make it easier for anyone who wants to try this, since splitting the ROM correctly was a... splitting headache. 29F1610 are out of production but plenty of NOS chips can still be found, just beware of fakes.
Here's how Tattletech reports the ROM before and after the upgrade. The sub-version changes from $30F1 to $30F2, so it's essentially Rev A. vs Rev B.
A couple of declaration ROMs are updated.
Last edited:
