Making modern iMac G3 Mezzanine peripherals

[Angelgreat]

Hello, so the revision A and B iMac G3's had the mezzanine slot and while it was intended for internal use by Apple, some accessories like the ForMac SCSI card and the 3dfx Game Wizard were developed for it. Items that also used the slot were Griffin's iDock

Now, I was wondering if new mezzanine cards cam be made for a iMac g3. I was thinking of a 3dfx Game Wizard with a built-in ForMac SCSI and a Griffin iDock, that way, you can play some intense games with a external monitor while also running it from a scsi drive. How cool would that be!

So for this idea, who would be interested in the Idea? Also, who would like to make them?

 

[joshc]

I don't think there would be much demand for them really. If someone was going to engineer something like this (taking considerable effort/time), there would need to be a big enough market to make it worth their while.

 

[cheesestraws]

Well volunteered, @Angelgreat, let us know how you get on... ;-)

 

[Angelgreat]

Well volunteered, @Angelgreat, let us know how you get on... ;-)

Well, I said in the post that ''who would like to make them'' Because I don't know how to make them. I was thinking of having someone like Bolle or Herd making them since they are going at reverse engineering cou cards and upgrades.

 

[demik]

Well, I said in the post that ''who would like to make them'' Because I don't know how to make them. I was thinking of having someone like Bolle or Herd making them since they are going at reverse engineering cou cards and upgrades.

Unfortunately reversing stuff from "recent" hardware is more difficult. You need more expensive hardware (logic analyser, scopes)... The weird thing about components is that "older" components are still available while more recent stuff is not.

For example, the SCSI Chip from the Mac SE/30 is still build in 2021, anything else... doesn't exists anymore.
It's definitively possible, but way harder than reversing stuff from the 68k era. Is there a pinout of the mezzanine connector somewhere ?

 

[Byrd]

@Angelgreat it's not as simple as you are proposing. TBH you might as well get a late model 500 - 600Mhz iMac G3 (that has a much better GPU than anything 3DFX made for games), plug in an external monitor and have fun - cost - $100 - 200.

 

[Angelgreat]

Ok, here's a concept image. It's a iMac G3 side panel. The Mezzanine panel would be a replica Sonnet Harmoni G3 pannel, but also have cutouts for S-Video and VGA. As for the card, my idea is a replica 3dfx Game wizard that also has a ForMac SCSI card and a Griffin iDock built in, albeat the db15 changed to VGA. I think it looks ok, anyone else?

 

[LaPorta]

You'd be asking people to cut holes in their Rev. A iMacs....I'd think that is a bit of a tall order, but I could be wrong.

 

[Angelgreat]

You'd be asking people to cut holes in their Rev. A iMacs....I'd think that is a bit of a tall order, but I could be wrong.

Sonnet's Harmoni G3 cpu upgrades for the iMac G3 came with their own panels that you can swap the original out with. The reason was if the User wanted to add the optional Firewire port that came with the cpu upgrade. I was thinking of having a similar idea to this for the mezzanine accessory.

 

[Cory5412]

A newer Mezannine card upgrade would be neat but one thing I think you should do is go review the recent thread where people posted pictures of mezannine hardware. In general, each individual card that exists is just about the maximum amount of additional hardware an iMac will fit.

With that in mind, unless you can radically alter how big each component is, I don't think you can fit all of those things onto a single mezannine card. a G3/G4 CPU can only get so physically small, and a SCSI controller can only get so physically small, so-on and so-forth. Plus, all those things need connectivity and if you were doing a multi-function upgrade you might need bridge or switch chips on the board, which themselves take up room.

You may be able to put, IDK, a single really really huge FPGA onto a mezannine card and do some neat things, but by the time you've added a new CPU, new graphics, a TV tuner, and SCSI to an iMac G3, you're most of the way to... just figuring out how the power circuit works and building a completely new motherboard. It would be a better computer, in the end.

So, to second what cheesestraws said - if you wanted to try your hand at this kind of project, maybe people have ideas on where to start in terms of documentation or projects you can do to get you primed for what you'd need for this one.

That said, though, if you want a G3 with scsi and a/v in and out and a faster CPU and a faster graphics card... maybe you do, really, want a PowerMac G3, a newer slot-loading iMac G3, or an iBook G3. All those computers have most of what you're asking for here.

This is kind of tangential here but one of the things that's most interesting about "limited" computers that have some but not a lot of expansion is seeing how people use the available expansion. The Mezannine slot in the early iMacs really is a great opportunity but when you're setting up a system, you absolutely have to think about what, specifically, you want a particular machine to do, and, unfortunately in this case "everything" isn't a realistic answer.

I like your optimism for the iMac G3, they're great computers in every sense... they just... aren't PowerMacs. And, the PowerMac G3, either a beige or a blue-white is really where people were going if they wanted to make no compromises at all.

 

[CC_333]

I like the idea!

However, I have to agree with @Cory5412 here. There's only so much room in there.

If anything, I think a functional clone of the Sonnet Harmoni would be practical, albeit nontrivial, so perhaps that might be a place to start?

And also, since only the Rev. A has a functional mezannine slot (Rev. B and newer deleted the slot, and the port cover lacks the factory-made cutout), the Harmoni is probably the only practical upgrade, since it'd be compatible with all revisions out of the box.

c

 

[Angelgreat]

I like the idea!

However, I have to agree with @Cory5412 here. There's only so much room in there.

If anything, I think a functional clone of the Sonnet Harmoni would be practical, albeit nontrivial, so perhaps that might be a place to start?

And also, since only the Rev. A has a functional mezannine slot (Rev. B and newer deleted the slot, and the port cover lacks the factory-made cutout), the Harmoni is probably the only practical upgrade, since it'd be compatible with all revisions out of the box.

c

The Revisions A and B have the Mezzanine slot. The revisions C and D remove the connector, but not the pads (making it possible to solder on a connector). The Slot loaders were the ones who removed the mezzanine pads.

 

[CC_333]

The Revisions A and B have the Mezzanine slot. The revisions C and D remove the connector, but not the pads (making it possible to solder on a connector). The Slot loaders were the ones who removed the mezzanine pads.

OK, thank you! That's what I thought, but I couldn't remember for certain.

So that means that, as a general rule of thumb, if an iMac is Bondi instead of any of the five fruit colors (which were only available on Rev C and D, I believe), then it likely has a functional mezannine slot.

c

 

[jeremywork]

Ok, here's a concept image. It's a iMac G3 side panel. The Mezzanine panel would be a replica Sonnet Harmoni G3 pannel, but also have cutouts for S-Video and VGA. As for the card, my idea is a replica 3dfx Game wizard that also has a ForMac SCSI card and a Griffin iDock built in, albeat the db15 changed to VGA. I think it looks ok, anyone else?View attachment 35063

Considering the motherboard PCB runs directly between the mounted ports and the mezzanine (except the modem; that's a daughterboard) I don't think a VGA port will fit there. (Not S-Video btw, that's a legacy serial port borrowed from the IrDA.) I'd sooner try to move the factory iPort PCB into the unfinished gray plastic area beneath the Mezzanine opening. If that works, you'd have a Harmoni + iPort and still have the Mezzanine completely free. Not sure how you'd get a GameWizard working alongside an iPro RAID without some logic-arbitrating slot splitter, and this would be very hard to fashion without offsetting the physical slot-alignment.

(I imagine with some dremeling this could work. There's a hard drive and optical assembly back in there, so might have to sacrifice the port door, though were you really going to fit all those cables through the door anyways? Possible that an SSD upgrade could help too...)

 

[Angelgreat]

Ok, I have another idea. The idea is to build a modern SD and CF card adapter for the iMac, that way, you can use SD cards and CompactFlash and transfer files between the modern web and the old mac. I think that would be useful.

 

[LaPorta]

Not a bad one, but would that not be much harder than just hooking the Mac to a network and transferring the files over ethernet?

 

[volvo242gt]

Could just use a card reader connected to one of the USB ports... Yeah, it'd be cool to have something integrated, but, it's simple to just plug in a card reader and copy files back and forth.

 

[Gorgonops]

The TL;DR about the mezzanine slot is it's *basically* a PCI slot, although all the discussions about it which really had any technical details are at this point almost two decades old. To go a little further, an oddity of the iMac and some of its contemporaries (Pismo and Lobard Powerbooks, for instance) is in fact basically the entire motherboards are just collections of PCI peripherals; the CPU card has the MPC106 system controller on it (which is basically the "Northbridge" part of the chipset in PC terms), which is why the memory also plugs into the CPU card, not the motherboard.

In theory at least if the signals are there for it you could probably hang a PCI-PCI bridge chip off the mezzanine slot and add the equivalent of another few slots to it; the resulting architecture would basically match what's going on in the B&W G3 desktop. (In that machine essentially the "southbridge" and the video card slot are directly on the MPC106's PCI bus, and the three 64 bit PCI slots are on a bridge.) In practice... yeah, that's a lot of work to go through; there probably is *somebody* out there still making a parallel PCI bridge chip, but they need software support, it's going to be a BGA-format chip, it's not a *sure* thing all the signals are actually on the slot... basically, you rapidly get to the point where you might as well talk about making a whole new motherboard for the system. And, hey, if someone wants to do it more power to them, but that's a lot of pain to go through for a 233mhz G3.

 

[CC_333]

What about implementing a mezannine-to-PCMCIA/CardBus adapter?

That way, rather than reinventing the wheel, it can benefit from all the various upgrades that are available to the PowerBooks, like Firewire, USB 2.0, SCSI, Wifi, sound, etc. Maybe even video, but I don't know of any CardBus-based video cards....

Since the mezannine is basically some form of PCI, and PCI-to-PCMCIA/CardBus adapters exist, then this seems like it could be reasonable to do.

c

 

[Gorgonops]

If it’s your bag then go ahead and try. Just be realistic when it comes to asking someone else to do it. Working early rev. iMacs are at this point pretty thin on the ground and, I know this is editorializing, they were never that much to write home about. Owned a couple myself, did the ATX mod to one after the monitor died, know first hand how completely useless they were under real operating systems…

Also just keep in mind that unless you plan on writing new drivers for everything on your wishlist your only source of parts for these projects is going to be recycling bins. Even if someone is still making a cardbus bridge chip (for what?) it’s pretty unlikely to be the same one used in a 1999 vintage Mac laptop. (Or register compatible with such.)