upgrading ROM for Macintosh II?

[ironborn65]

hi all,

is it possible to replace the ROMs of the Macintosh II with 800k floppy with the version of the one with FDHD?

from this 

1987-12 - 9779D2C4 - MacII (800k v2).ROM

to this 
1988-09 - 97221136 - Mac II FDHD & IIx & IIcx.ROM

thanks! 

 

[360alaska]

Yep, I actually got a dead IIcx board for the roms and used a FDHD SWIM from a MAC SE with an adapter.

 

[ironborn65]

so, do I just need to download the ROMs and burn 4 27C512? 

 

[davidg5678]

I may be wrong here, but I think that there is more to HD floppy support than just ROMs. I think there is a SWIM chip that also is required in addition to ROMS for this to work. I believe that this is how Mac SE floppy upgrades work, at least.

 

[ironborn65]

in https://everymac.com/systems/apple/mac_ii/specs/mac_ii.html I read

"With the FDHD upgrade kit, the system is capable of supporting 68 MB of RAM (1 MB SIMMs in bank A and 16 MB SIMMs in bank B)."

I was wondering if a ROM upgrade from the iifx could do the trick, @davidg5678 is saying a SWIM chip is to be replaced as well.

Is anyone aware of what the FDHD upgrade kit for Mac II consist of?

 

[karrots]

Per wikipedia the Mac II shipped with a IWM. Which is how my board is labeled. Pretty sure the get what you want you need to swap the IWM for a SWIM.

 

[cheesestraws]

I was wondering if a ROM upgrade from the iifx could do the trick, @davidg5678 is saying a SWIM chip is to be replaced as well.

Upgrading the ROMs will not magically make an FDHD floppy drive work.  The IWM or SWIM is the chip that generates the signals that actually control the floppy drive.  The IWM cannot drive an FDHD drive.  The SWIM is the upgraded version which can.

 

[ironborn65]

ROM does magic sometimes ....  

thanks for the reply, I did not know that, I did no find any SWIM chip for sale, is it something that is usually done as an upgrade?

 

[Franklinstein]

Back in the day the SWIM chip was available as an upgrade part; I think it's listed by model number in one of Larry Pina's books. The SE could also be upgraded to FDHD in the same manner. Offhand I don't know the various revisions of the SWIM and which were compatible where, but it's possible you could pull a SWIM from a junk board (probably SE FDHD, SE/30, or other member of the II family) and install it in yours. It should be a PLCC-type chip so just make sure the leads are clean after you desolder it (if necessary) and it should drop straight into the socket on the II's logic board.

Anyway the official Apple upgrade to a Mac II FDHD was a set of ROMs, a SWIM, and one SuperDrive along with an "FDHD" sticker to put on the case next to the upgraded drive so you could differentiate it at a glance from the remaining 800k drive. Again, the SE FDHD upgrade was basically the same.

 

[360alaska]

Here's and Idea f the hack I did: