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iMac G3 (Rev A -> C) G4 CPU Upgrade

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13 hours ago, Compgeke said:

Worthy of note on the IBM computers with a ZIF: They're just a CPU card without any cache or anything. Good chance it's just the 60x bus directly on the pins from the CPU, possibly even in the same pinout as the BGA chip. If someone wants to grab one and desolder the chip, it'd be possible to cross reference the chip datasheet and the BGA pads to pins. A lot of work, but doable. I've attached the datasheet that has the pinout to this post.

 

Another IBM note: they won't work with cards that have an onboard L2 cache like the Macs have. Trying a 450 MHz G3 CPU (PPC750L-EB0A450) in an RS/6000 43P-150 will throw an E24C "L2 cache array test fails." error. Knowing the pinout would be interesting as it may be possible to make a G3/G4 upgrade for the 43P-150 (and B50). Not that it'd be a worthwhile time investment, I doubt all 3 of us with such a system would be super interested.

604eBGA_Datasheet.pdf

 

indeed I have noticed those 300 pin ZIF 604 CPUs I have been meaning to pick one up to play with but I dont fee like paying £40 for a 20 year old CPU :) but indeed I too would not be surprised if its just the 60x bus in a socket :) I want to try one of these 604 ZIF CPUs in one of my BW G3s (I know they work in G3 beiges)

I have wondered what a G3 ZIF might do in those IBM Machines, its interesting that the machine can even detect the L2 Cache in the first place that is on the Backside bus. unless does the IBM machine have any motherboard L2 Cache? if so can it be removed? I know in Beige PCI Macs it helps to remove the onboard L2 if your installing a CPU that has its own L2. (im not very familiar with these IBM machines so i dont know how the cache is done on those)

have you tried a slower G3 ZIF (or one with less L2)? how is the multiplier set on these? maybe the Lobo cant handle 450Mhz CPUs/speeds. it would also be interesting if a G4 ZIF works (and as Dan says if a 750FX/GX works...)

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The real issue with the IBMs is they have their own non-removable motherboard cache and as such don't like having it on the CPU. If I had a G3 ZIF without any cache it just might work.

 

No idea on how they handle multiplier. They were offered in two different versions, a 233 MHz 604 and the 375 MHz one so they do support adjustable multiplier and bus. Probably resistors on the CPU card itself. Of course, there's almost no documentation on the IBMs. 

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2 hours ago, Compgeke said:

The real issue with the IBMs is they have their own non-removable motherboard cache and as such don't like having it on the CPU. If I had a G3 ZIF without any cache it just might work.

 

No idea on how they handle multiplier. They were offered in two different versions, a 233 MHz 604 and the 375 MHz one so they do support adjustable multiplier and bus. Probably resistors on the CPU card itself. Of course, there's almost no documentation on the IBMs. 

 

http://ps-2.kev009.com/rs6000/redbook-cd/sg245144.pdf

 

found this has some interesting info but nothing on the clock multiplier for the CPU sadly

 

I do know when those 604e ZIFs are installed in G3 beiges the CPU speed is still set by the motherboard Jumpers, So I dont think the IBM ZIF CPUs have onboard PLL resistors but I cant say for sure. http://www.applefritter.com/?q=node/24331 https://web.archive.org/web/20140108030322/http://www.ppcmla.com/press/?p=61

 

is it possible to try and disable the L2 cache by removing some resistor or something? like on the 9600 Tsunami boards...

 

I also wonder if its worth trying one of these G3 ZIFs that had all IBM components. (these used PPC750Ls and weird IBM BGA L2 cache) kinda rare but iv seen them show up on ebay from time to time. I got this photo from the G3 BW service manual as there are none on ebay atm...

 

image.png.d9c0127ec152ba4807570948164ba9ea.png

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1 hour ago, Dandu said:

I have tried a PowerPC 604 from an IBM machine on my G3 BW : it will not boot, with a long beep. 

I remember reading about that on your blog (yay for google translate :) ) but I cant seem to find the article these days

 

which CPU did you try I have noticed theres 2 types of 604 ZIFs one older? black type where you cant see the CPU it self, and a newer type which is a PCB with a 255CBGA 604e with a little metal cap slapped on top both seem to be 300 pin ZIFs tho. also did you try dropping the bus speed down to 66Mhz? (I dont know if the 604e supports a 100Mhz bus speed)

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31 minutes ago, Dandu said:

This one (in the center)

 

 

IMG_1656.JPG

 

interesting :) id expect that CPU to work in a G3 BW, did you try and drop the FSB down to 66Mhz? (also might be worth running the G4 CPU patch, which stops the G3 BW from complaining about unsupported CPUs)

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(forgot to mention, the L2 cache in the iBook, according to the L2 Cache chips data-sheet it says it works at both 3.3V and 2.5V, seeing as the L2 cache is working fine with the 7410 im guessing its running at 2.5V in the iBook I guess I could check with a DMM at some point to find out for sure :) )

Edited by LightBulbFun

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so im happy report some good new developments in the world of swapping CPUs around :):)
 
the first one relates to Core voltage of various PPC CPUs, since the start of this whole thing we had been wondering how do we check the Core voltage of various PPC CPUs/Macs when yesterday it hit me, we can just measure across one of the many Bypass/filter capacitors that go between GND and the Core voltage rail, people do this all the time on MacBook logic-board repair to make sure the CPU is working so I thought why not apply it to PowerPC macs, I gave my Pismo a quick probe this way and I was able to record a Core voltage of 2.045V which is exactly what id expect (the PPC750L is said to have a core voltage of 2V)
 
the other one is to do with, Motorola G3s the MPC750 and XPC750 CPUs, it was thought that all the Motorola parts all had a core voltage that was too high to work with the 7400/7410 CPUs but I did a bunch of internet sleuthing and as it turns out that is only true for the earliest of G3s, but the later ones, actually have a Core voltage that is compatible with 7400-7410 CPUs :):) the way to tell which 750 is which. is
 
the 2.6V XPC/MPC750s have say on the second line on the chip "ARX" followed by clock speed. the 1.9-2.05V G4 compatible MPC/XPC750 chips say "PRX" followed by the clock speed
 
here is a picture of a "PRX" G3 from a Rev A 400Mhz G3 BW (I measured the core voltage of this one and got 2.045V as well :):) )
 
upload_2018-2-14_8-20-19-png.751225
 
this opens up a few more Macs/CPU cards to being G4 upgraded now :):)
 
but the issue still remained of what about the Bus voltage and L2 cache voltages, on the PPC750L 7400 and 7410 the L2 voltage is configured by a pin that is pulled to various states, where as the XPC/MPC750 only supports 3.3V, so these voltage configurations pins are just unused pins on the XPC/MPC750, luckily for us on the 7400-7410 these pads have an internal pull-up which configures the CPU to use the highest Voltage its compatible with, which on the 7400 is 3.3V for both the bus voltage and L2 cache voltage which is the same as what the 750 supports their-for solving those issues :)(this explains how the L2 cache continued to function on the Sonnet nuBus G3 card @Bolle stuck a 7400 onto :) )
 
(the Rev 11.3 7410s found in Apple machines are only compatible with 1.8/2.5V bus and L2 cache voltages, but the Rev 11.4 7410s like the ones on ebay are compatible with 3.3V bus voltage but only do 2.5V L2 cache still, so if your planning to G4 swap an MPC/XPC750 machine/CPU card I recommend using a 7400 and not a 7410)
 
if you can adjust core voltage then you XPC/MPC750A based boards should work too with a G4 7400 :)
 
for those looking for the Juicy technical stuff and my references ill link bellow some data sheets and PDFs that helped me figure all this out :)
 
 
 
 
 

 

(this is a copy paste more or less from a Post I just made on MR as well so sorry if theres any formatting bugs or the like :p )

Edited by LightBulbFun

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@dosdude1 is at it again, this time upgrading a Trayloader iMac G3. He's figured out how to change the core voltage on the card, which is necessary when the G3 chip on the card is a ARX Motorola 750, which run at higher voltages that will damage the Motorola 7400 G4 CPU (see the previous post for more info). @LightBulbFun and I have been trying to figure out what sets the Vcore on these cards, so I am very glad @dosdude1 and him figured out that a set of specific resistors does this. 

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