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So, I bought a 1GHz 7455...

lepidotós

Member
...and was told to come here. I've waited and read up on what I was confused on, and now I'm pretty sure I understand things. Still, I don't really know where to begin on actually getting the processor upgrade built. I can solder and all, but I've only just been around PowerPC Macs for the last month or two. Any guidance?
I'd like to have everything on sockets if possible, that way if one of the chips dies I can easily switch it out. Is that generally not a problem in people's experience?
Is this even a feasible project nowadays? The computer is a 450MHz Sawtooth, seemingly from early 2000, but it seems to have an early motherboard since the power button LED is green, which from what I hear is what was on the earlier computers.
Thank you!
 

Byrd

Well-known member
Welcome,

Sounds like you're looking for a processor desolder and swap - which is feasible on some aftermarket G4 upgrades, but less common on stock Apple CPU daughter cards owing to having slower cache that can't keep up with the newer CPU. I don't think you're going to get far using the stock daughter card in this instance.

@herd is a member here that would know much more than me, on Mac Rumor forums member dosdude1 also has good knowledge.

JB
 

CircuitBored

Well-known member
More information is needed before we can provide much insight into your 7455. Did you buy a Macintosh CPU card or just the PowerPC CPU that sits on it? If you bought a complete card then it's a matter of checking it's compatible with your Sawtooth and then installing it.

If your card is a single 1GHz made by Apple then it will not work in a Sawtooth. The only 1GHz 7455 cards that will work in a Sawtooth are dual-CPU designs from later Quicksilver G4s. If you have a dual 1GHz card from a Quicksilver then it will work provided you apply a 12V power source to the mounting screw that sticks out from under the heatsink when the card is mounted (I can provide a picture if you need it).

If you've simply bought some NOS 7455 chips then you should listen to @Byrd. Chip swaps are hard work but not impossible. Unless you're doing this for "the climb" then I'd recommend simply buying a pre-upgraded CPU card.
 

lepidotós

Member
More information is needed before we can provide much insight into your 7455. Did you buy a Macintosh CPU card or just the PowerPC CPU that sits on it? If you bought a complete card then it's a matter of checking it's compatible with your Sawtooth and then installing it.

If your card is a single 1GHz made by Apple then it will not work in a Sawtooth. The only 1GHz 7455 cards that will work in a Sawtooth are dual-CPU designs from later Quicksilver G4s. If you have a dual 1GHz card from a Quicksilver then it will work provided you apply a 12V power source to the mounting screw that sticks out from under the heatsink when the card is mounted (I can provide a picture if you need it).

If you've simply bought some NOS 7455 chips then you should listen to @Byrd. Chip swaps are hard work but not impossible. Unless you're doing this for "the climb" then I'd recommend simply buying a pre-upgraded CPU card.
It's just the chip itself, a Motorola XC7455A-RX1000PF according to the source, singular though I might get one or two more since they're not super expensive just to have handy. I have my doubts that the computer would accept the dual-processor upgrade, seeing as it seems to be an early motherboard, but it's possible since the serial number suggests an April 2000 build date and the case definitely states 2000 at least.
I'd like to build my own board from scratch, if possible. I have some experience in working on PCBs (both getting the PCB printed, and assembling it from there) from the time I made a Game Boy flash cart, though I acknowledge my inexperience. Everything I read says that the 7455 can use 2MB of L3 cache, and my board probably definitely doesn't have any traces for it because why would you put an L3 cache spot on a 7400 board, so using my old one is out of the question and a third party upgrade board is out of my price range, assuming one ever does show up on eBay. And I'd like to keep my CD drive working, which a QS CPU apparently doesn't let you do, so that's definitely something of a last resort. Plus, it means one more upgrade card stays available for someone else to buy.
 
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Byrd

Well-known member
I admire your ambition! If I can understand what you want to do (transplant a single 7455 onto a stock Apple 7400 board?), unfortunately this isn't going to happen without significant electronic engineering, costs and time. A dual CPU on a Sawtooth is possible, but at diminishing returns noting the slow bus to pump it all through, you'd be better off finding a QS or MDD for upgrading.

Third party upgrades are around and some have been advertised here for fair prices; they come up often on eBay if you search for the usual manufacturers: Sonnet G4, Gigadesign, Powerlogix - give it a couple of months and something will come up.
 

lepidotós

Member
I admire your ambition! If I can understand what you want to do (transplant a single 7455 onto a stock Apple 7400 board?), unfortunately this isn't going to happen without significant electronic engineering, costs and time. A dual CPU on a Sawtooth is possible, but at diminishing returns noting the slow bus to pump it all through, you'd be better off finding a QS or MDD for upgrading.

Third party upgrades are around and some have been advertised here for fair prices; they come up often on eBay if you search for the usual manufacturers: Sonnet G4, Gigadesign, Powerlogix - give it a couple of months and something will come up.
You don't. I aim to get a whole new PCB printed and stick the chips on that, nothing Apple or third-party. I completely ruled out the 7400 board for its lack of spots for L3 cache. As for the upgrade boards, my total budget is about $75-100 at most; those boards cost upwards of 19 times what I paid for the computer itself. Considering I only have about two thousand to my name, that eats up a whole quarter of every penny I have.
 
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Byrd

Well-known member
I'm trying to help to steer you in the right direction with the limited information you've provided. Good luck.
 

lepidotós

Member
I didn't think I was giving limited information, but let me get excruciatingly detailed because it seems that we have different standards on that front.
I bought just a chip, a Motorola XC7455A-RX1000PF, and my end goal is to have had a CPU daughter board custom printed for it, and each piece held in a socket when possible for easy repair. I'm not interested in using Apple's daughter board, either my own that's currently in my computer or one from another computer, nor am I interested in using a third-party upgrade board, as they are out of my budget. I've already used PCBWay to print a board for another project, so getting a board printed isn't a big problem for me. I also want to get a board printed rather than reusing another board so that I don't use up another board someone else could have used, and I can keep my Apple board in case my homemade upgrade dies on me.
The computer I plan to install it in is a Power Mac G4 (AGP graphics) with currently a single 450MHz CPU, that hasn't been modified in any way from stock besides a larger hard drive and more RAM; currently it has 640MB since the smallest of the four RAM sticks has died overnight. It was built in April of 2000, and running UNAC tells me it has the Revision 7 ASIC, so I could install two processors if I wanted. I only have one, but I'm now thinking of installing two, and giving each their own L3 cache.
If there's an already designed circuit board that I can send to get printed, or if there's anyone that can help with getting one designed, that would be really helpful.
 

Bolle

Well-known member
I am not sure if you thought this through…
First of all PCB designs for selfmade G4 CPU daughterboards do not yet exist, so you’d definitely have to make your own design here.
From a theoretical view those daughterboards are nothing too complicated.
They just connect the CPU bus and control signals from the logicboard right to the actual CPU. What’s left is some sort of power supply to generate the core voltage for the CPU and several voltages for the L3 cache and cache bus.
The CPU core voltage has to be somewhat precise and deliver some current so usually a buck converter circuit is used on the boards that already exist.
On top of that you need a frequency generator of some sort that will satisfy the timing requirements of the CPU you’re using.
You’ll have to reverse engineer the pinout of the logicboard connector as I don’t think there’s any documentation on it yet.
It might not be easy to find modern parts that will nicely match all the requirements of the 745x.
That would mean you have to find new old stock parts for the clock generator, buck controller… is the logicboard connector that those daughterboards use still made?

After adding up all those parts, cost for the (at least 6 layer) PCB, time to design, route and test the boards you’ll definitely end up with 10 times the cost of a third party upgrade from ebay.

A CPU board with high frequency components doesn’t compare well to a gameboy cartridge from a complexity point of view as well as the engineering effort that has to go into it.
I’ll whip up a gameboy cartridge design for you in a few hours. A G4 CPU board is more on the scale of taking months to engineer.
 
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lepidotós

Member
Sounds like a challenge, but I'm willing to look into doing it. I guess it was... optimistic to hope someone had already done it, or had the designs of the commercial boards on hand. Spreading the cost out over months is fine, I just can't justify an upfront $600 price. The particulars of why are both numerous and irrelevant but there's reasons. I already had one hardware RE project in the works for something else, so one more is good practice.
I'll look into doing it, and if I make any progress I'll make sure to release what I've gotten. Considering 74xxes are from what I can tell still being made, there should be at least mostly-compatible parts out there to use for them. Maybe that's also just optimism, but I'm willing to take a look.
Thank you for the information, I'm not good at showing it (especially online,) but I am thankful for it. We'll see if it pans out. If there's anything else I'll need to know going in, it would be very helpful.
 

herd

Well-known member
Assuming you already have the tools and experience to solder 500pin chips, then I think the cheapest way to connect that chip to your computer is to buy a used quicksilver CPU board and solder it on there.
 

John8520

Well-known member
Can you expand on this? What does a CD-ROM drive have to do with building off of a quicksilver CPU module?
 

Byrd

Well-known member

You lose the second IDE connector, but not the CD-ROM drive if you want to set it off the slave connector off your first IDE connector, or look into an ATA/SATA PCI IDE card.
 

John8520

Well-known member
Ahhh okay, interesting, it's a physical issue. I'm curious as to how much wiggle room there is in the process.
 

herd

Well-known member
Perhaps you could try soldering a 40-pin connector as a warmup for what you plan to do.


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