Mystery iMac logic board traces

[Dennis Nedry]

I have noticed on an old 333 MHz iMac logic board that there are traces for what appear to be:

J12 = Mac floppy drive

J11 = CD analog audio

J4 = Serial port (Used for IrDA in original bondi iMac?)

J2 = ADB port

J6 = Marked "IrDA"

DS2,3,4 = Ethernet connection/activity LEDs

S2 = mystery button/switch

MEZZANINE = some crazy slot on the bottom of the board

Does anybody know about these or if they'll work if a connector is soldered on? I think I'm most interested in the floppy and ADB ports.

 

[Dennis Nedry]

I just mounted a connector onto the floppy drive port and tried it. The drive is getting power, it spins when you insert a disk.

 

[LCGuy]

J12: It was actually a common hack back in the day to mount a 20 pin boxed header here and connect a surplus Mac floppy drive to it - worked out cheaper than buying a USB FDD, if you knew what you were doing, and saved a USB port. It was basically a case of soldering the header on, connecting the cable, running it out the side of the iMac, and plugging the drive in.

J11: No clue, I'll have to have a look at my spare.

J4: Yes, this is a serial port, used for the IrDA module in the Rev. A and B Bondi iMacs.

J2: Yes, this is an ADB port, provided you solder on some resistors and a few other things, you can use ADB devices on an MiniDIN-4 connector installed here. I remember seeing a page where some Japanese guy had managed to get it working.

J6: On the Rev. A and B Bondi iMacs that have IrDA, this has a cable connected to it, that goes to the serial port on the bottom, in the same fashion as what you see with the video and audio connectors.

DS2,3,4: I've never noticed these before, to say the least, I'll have to have a look! interesting.

S2: No idea, I'll have to have a look at mine.

MEZZANINE: This is where the Mezzanine slot is installed on the Rev. A and B Bondi iMacs. This was put in by Apple for testing purposes, but seems to offer access to the iMac's PCI bus. After this was discovered, a couple of cards were actually made for this slot - MicroConversions made a version of their Voodoo2 graphics accelerator that fit this slot, and someone else made an UltraSCSI card. Best of luck finding either of them though.

 

[Dennis Nedry]

After playing with the drive for a while, I was unable to get it to actually read a disk. It is getting power because it spins for a moment after a disk is inserted, but it seems that nothing else is happening. I did actually solder a header onto the motherboard to do this, so I'm pretty sure this is a good connection I'm making.

I would like to see how to get ADB working! That would be cool. When I search Google for it, I only find some thread in this very forum which doesn't really say anything about how to actually do it.

 

[Bunsen]

I assume you're using OS 9 or earlier to try and read the floppy, being as there's no support in OS X

 

[Dennis Nedry]

Yep, booted into OS 9 and the drive didn't do much except spin and then stop. I also tried inserting a disk before booting and nothing much happened. You would think it would spit the disk out if it isn't bootable.

This is not the original 233 MHz iMac logic board, though, this is the 333 MHz one - maybe that makes a difference? I noticed that the 233 one has an actual port mounted at J4 for the IrDA but this one doesn't, only the traces are there.

 

[Rodus]

^^digging around it looks like the floppy port will only run on systems below 8.6, if the iMac has had the firmware update applied for OS X then that too could be a factor.

 

[Dennis Nedry]

From what I gather, 8.6 is the minimum that will run on this iMac, and you say it would need less than 8.6. Does that mean there's no way to get this to work?

 

[Bunsen]

I am 99.99% certain these hacks will only work on a 233Mhz Rev A board.

 

[LCGuy]

Which reminds me..one of these days I've gotta find a Rev. A iMac somewhere...would be a neat machine to play around with, not to mention that if I keep it original and in good nick, it might be a good investment......

 

[Dennis Nedry]

I am 99.99% certain these hacks will only work on a 233Mhz Rev A board.

Make that 100% on the floppy drive. Maybe there are further hacks that can be done to make it work somehow, but there's no way to just solder on a connector and expect it to work on a 333 MHz board.

 

[Bunsen]

I'm pretty sure that ROM support for those devices was removed after the Rev.A machines.

Luckily you can drop a 333MHz CPU module into a Rev.A : - and a bare Rev.A board should not be too hard to locate on evilBay

 

[Mike Richardson]

It needs a SWIM chip too doesn't it? Maybe that chip is gone, but the power is still hooked up, so the floppy drive powers on and starts to read the disk but then nothing is there to really control it so it just sits there.

It's interesting that they mounted SWIM chips on all the Rev. A iMacs for a non-existent floppy drive.

 

[soopergrape]

I was just looking around for someone interested in a Voodoo 2 card for the Mez slot of a Bondi iMac and found these posts. I heard it was disabled with the 1.2 firmware "update." Don't know if I did this one, but I do know I took a speed hit from an unidentified source. The flyback coil went so I never got around to identifying it. I still have the Voodoo 2 Mezzanine card and the installation CD that came with it. I also have the motherboard, but it may not work with the mez slot if I took the slot disabling firmware kool-aid.