iMac g3 tray and Wallstreet CPU interchangeable?

[indibil]

Hi, a quick question. At first glance, they seem to have the same motherboard connector. I have an iMac G3 tray with a failing CPU card, and I could get one from PB G3 Wallstreet. Has anyone tried it?

I know the fault is the CPU card because I put one in from another iMac I have, and it works then.

 

[croissantking]

I noticed that they look very similar as well. One thing to note is that the ROM is different, so if you managed this you’d have an Old World iMac.

My hunch is probably there is a minor difference in the connector to stop you physically plugging one in. If that’s not the case, I wonder if it would work at all, or even partially. The ROM difference likely means that OF/Toolbox drivers would be missing for some of the iMac’s hardware. The pinout on the connector could be subtly different too, which is a bit worrying. Comparing schematics would be the way to verify this, but unfortunately none are currently available for the Wallstreet.

It would be an interesting experiment, but not if you’re looking for a quick solution rather than a project.

 

[Daniël]

It is something I've been curious about myself.
The thing is, the iMac G3 schematics do actually reference the Wallstreet card, naming it "SUV (WS)" in a voltage setting comparison chart with Columbus' (the codename of a hardware design for a scrapped netbooting client, repurposed for the Trayloader) "Humvee" card.

That implies the designs are at the least related to one another, likely being that Humvee is based on SUV.
The interface from the card to the main system is basically just power, a PCI bus, and some miscellaneous signals like I2C, so there's a good chance the pinout might be similar or the same.

That said, yes, the ROM is on the card, and you would have to replace that with the iMac's ROM in some fashion.
That would be the biggest hurdle by far.

 

[indibil]

Thanks for the replies. Is the ROM chip the same in the Wallstreet as in the iMac? The photos I have include RAM, and I can't see it. If I just need to unsolder the one from the iMac and solder it to the Wallstreet, I could do it. If I needed to program, I'd have to find an adapter for the TL866 that would allow me to do it, but I'd have to have the ROM file.

 

[croissantking]

It’s a totally different footprint

 

[indibil]

I'm afraid they don't have the same ROM chip; the iMac only has one, and the Wallstreet has four. It probably doesn't work.

 

[Daniël]

Yep, and they all have Apple part numbers as far as I know, meaning it'll be hard to tell if there are off the shelve programmable ROMs that could fit in their place, and if these follow any sort of standard that ROM programmers can handle with regards to reading and programming them.

 

[indibil]

Well, I'll try it: €30 for the processor with two RAM modules and several parts from the Wall Street motherboard. But I'm afraid it won't be easy, otherwise it would have been done already.

 

[croissantking]

Trying to boot with the Old World ROM would be more interesting imho

 

[indibil]

Yes, the first thing I'll do is put in the unmodified CPU card, let's see what happens, but probably nothing will happen, I highly doubt I have a desktop iMac Wallstreet

 

[Daniël]

The best way would probably be to figure out a method to flash the iMac ROM onto the Wallstreet card, inside of a PowerBook G3 WS.
Apple's flashing utilities will have methods of verifying whether the ROM is valid for the machine, so those would have to be patched out or otherwise overruled.

Trying to boot with the Old World ROM would be more interesting imho

I wonder whether that'd work at all, given the Wallstreet uses the Heathrow chipset, vs. the Paddington chipset in the iMac.

 

[indibil]

I don't have a Wallstreet, so I couldn't flash the ROM from a Mac.

So the chipset wouldn't be compatible? They both use a 66MHz XPC106.

 

[Daniël]

I don't have a Wallstreet, so I couldn't flash the ROM from a Mac.

So the chipset wouldn't be compatible? They both use a 66MHz XPC106.

That's the main chipset, which also handles the PCI bus.
The Heathrow and Paddington I/O ASICs sit on that PCI bus, and handle everything from the IDE interface, floppy interface, Ethernet, etc.

I'm not 100% certain, but if they need code in the ROM for the system to be able to use these ASICs, running a ROM from a Mac with a different I/O ASIC might cause it to not boot at all, or not be able to boot any OS as it can't interface with any I/O.

 

[croissantking]

I wonder whether that'd work at all, given the Wallstreet uses the Heathrow chipset, vs. the Paddington chipset in the iMac.

They’re pin compatible as you previously noted here

 

[Daniël]

They’re pin compatible as you previously noted here

They are, but I'm not certain they'd work 100% the same with identical ROM code, if they do need support from the ROM.

 

[croissantking]

So the chipset wouldn't be compatible? They both use a 66MHz XPC106.

XPC106 is the northbridge and Paddington is the southbridge.

 

[croissantking]

It is something I've been curious about myself.
The thing is, the iMac G3 schematics do actually reference the Wallstreet card, naming it "SUV (WS)" in a voltage setting comparison chart with Columbus' (the codename of a hardware design for a scrapped netbooting client, repurposed for the Trayloader) "Humvee" card.

What other off-road vehicle names did Apple use for their CPU cards?

I only realised recently that Columbus fits the whole new world thing.

 

[cheesestraws]

What other off-road vehicle names did Apple use for their CPU cards?

SWIM.

*ducks*

 

[croissantking]

SWIM.

*ducks*

Are you trying to be silly

 

[cheesestraws]

Are you trying to be silly

I'm honoured by the fact you think I could ever be anything else