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PowerPC 7457 upgrade for iMac G4
- Thread starter re4mat
- Start date
Unknown_K
Well-known member
I have a dead Daystar that needs a PPC601 chip but for $100 and desoldering effort I could just buy another Daystar (I won't).
People need to make money, so you get price gouging. Some people think all this stuff should be free, until they give something valuable away and see the buyer flip it on Ebay 5 minutes later.
People need to make money, so you get price gouging. Some people think all this stuff should be free, until they give something valuable away and see the buyer flip it on Ebay 5 minutes later.
Daniël
Well-known member
True, but the effect of someone buying the way overpriced $360 7457 has already caused another eBay ad to pop up for the 7457... also at $360. That seller saw it sell for that utterly insane price, and now wants in on it. And so, the price will remain that high.
Unknown_K
Well-known member
You assume somebody else doesn't have that chip and will want a quick sale at maybe $300 and somebody else will end up undercutting that. Prices stay high when there is great demand or very little supply.
Some items are so cheap on Ebay I don't see how they make any money.
Some items are so cheap on Ebay I don't see how they make any money.
tanaquil
Well-known member
I wouldn't mind so much if it weren't for the fact that ebay apparently represents "Best Offer" amounts accepted as the original asking price, not the price actually paid. That leads to rampant inflation!
At least if it were true that someone ACTUALLY paid xyz inflated price, there would be an argument to be made for "market will bear," etc.
At least if it were true that someone ACTUALLY paid xyz inflated price, there would be an argument to be made for "market will bear," etc.
Unknown_K
Well-known member
Reasonable means different things to different people. Line up 5 people and put a computer in front of them and tell them to write a reasonable offer on a sheet of paper and them compare. Same with giving it away, it could mean the here take this for free, or it could mean charging $100 for something that might be $500 on ebay. Everything is subjective and the markets are different in each city and country because of supply, demand, and personal finances of both parties involved.
Daniël
Well-known member
Going back on topic, @dosdude1, with the help of @LightBulbFun, found out that the GigaDesigns G4 Patcher will work with the iMac G4. He managed to upgrade his USB1.1, 1GHz iMac G4, to a 1.67GHz 7447B processor from a PowerBook G4, overclocked all the way to 2GHz. This patch will likely also work for the 7547.
CC_333
Well-known member
Truer words have never been spoken!
I miss the eBay of 2005, which was simpler to navigate, and had a search function that actually worked without extra rigamarole.
I'm not fond of all their stupid advertising pop-ups, pop-overs, pop-unders, pop-ins and pop-outs either; I feel like they're trying to pop me into submission!! *Especially* on the home page! I would prefer just a simple search box with a few links to browse various categories, like it used to be!!
c
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And this is why I don't bother to browse and rarely search Ebay any more. I'll go there for a specific item, usually after finding the part number somewhere. I find no joy, only frustration in trying to browse Ebay for vintage Apple products and accessories. That was something I used to really enjoy and put some time into.
techknight
Well-known member
So with that out of the way, Where are the alternatives? anyone other than ebay that has more than 5 items of interest?
re4mat
Well-known member
Nice! I've already got v2.1.0 and v3.0.1. The Readme for 3.0.1 does say that it also works on the 7457:
re4mat
Well-known member
This project is not dead! 
My workshop is now almost fully set up, though I do still need to decide what my BGA rework solution is going to be. I've been doing a tonne of research for this project, which resulted in some documents that some might find useful.
First is a map of the pins/signals for the 745x chips, as well as the SRAM chips that the schematics specify should be used for the L3 cache. What's that you say? L3 cache in an iMac G4? Oh yes! Turns out the 820-1257 board is wired up for an L3 cache, but Apple just never populated it. It looks like there's just a small handful of resistors (4 pulldowns and two 0Ω resistors) that configure the machine to bypass the L3 cache. The schematics list all the components necessary for populating the L3 circuits (voltage regulator, pullup/pulldowns, filters, etc.) and where to put them. So unstuff the NOL3_CACHE resistors, and stuff the L3_CACHE components, and that should do it. (In theory.) It's worth trying, anyway. And even got a couple of the SRAM ICs (Samsung K7DB03671B-HC25) for about $30 a couple months ago on eBay.
Anyway, the pinout/signal map is a Numbers file with the columns and rows laid out like the pins are in the datasheets. I wanted to make doubly sure that the 7450 and 7457 were actually pin-compatible, and to make sure that those pins match up with the signals in the schematic. So in each cell, it lists the name of the pin according to the datasheets for the 7450, 7455, and 7457, and the last line is the signal name on the PCB, according to the schematic. Cells with a red outline indicate pins that didn't match up 100%. (But from what I can tell, should be fine.) I find it a lot easier to read than the pinout/signal list in the datasheets.
The second file is an Omnioutliner file for the PLL configurations, showing the bus multiplier in the leftmost column, with the other columns showing what the PLL config is for the 7450, 7457, and according to the iMac schematic, respectively. Made it a lot easier to see the differences in PLL configs between the 7450 and the 7457, showing that for the most part they line up. I'm uploading it here as a PDF because maybe not everyone has Omnioutliner.
Also made a Soulver file to run some numbers, but I'm not going to upload that. It's just a little utility for me to figure out power consumption, using available data from the datasheets. (Imagine that! Data in a datasheet!) I was able to use it, though, to determine that I will need a beefier power supply, especially with the L3 cache. Basically, with everything configured the way I want, I'll be pulling ≈12.2 more watts than the original configuration. (I love when electrical work gets all mathy. ) So I found someone who was parting out their USB 2.0 iMac G4 and bought the power supply off of them for $20. 160W, which is 30 more than what the iMac currently has, which should cover the difference with more to spare.
Of course, 30 more watts means more heat, so the exhaust fan is definitely going to need to be beefier. I'm still looking into that. Also, the 160W PSU has a 16-pin molex connector, rather than the 14-pin on my iMac. Not an deal-breaker, though; all the signals are the same, with the addition of an extra pin going to ground and an extra pin going to FireWire power directly, which is an interesting quirk of the USB 2.0 iMac. But if you took those pins off, then the pinout is the same as the 14-pin molex. So that should be pretty easy to adapt.
All that said, I decided that I'm going to work on the compacts first before I get to the iMac. They definitely need more love at the moment to get to full working order.
My workshop is now almost fully set up, though I do still need to decide what my BGA rework solution is going to be. I've been doing a tonne of research for this project, which resulted in some documents that some might find useful.First is a map of the pins/signals for the 745x chips, as well as the SRAM chips that the schematics specify should be used for the L3 cache. What's that you say? L3 cache in an iMac G4? Oh yes! Turns out the 820-1257 board is wired up for an L3 cache, but Apple just never populated it. It looks like there's just a small handful of resistors (4 pulldowns and two 0Ω resistors) that configure the machine to bypass the L3 cache. The schematics list all the components necessary for populating the L3 circuits (voltage regulator, pullup/pulldowns, filters, etc.) and where to put them. So unstuff the NOL3_CACHE resistors, and stuff the L3_CACHE components, and that should do it. (In theory.) It's worth trying, anyway. And even got a couple of the SRAM ICs (Samsung K7DB03671B-HC25) for about $30 a couple months ago on eBay.
Anyway, the pinout/signal map is a Numbers file with the columns and rows laid out like the pins are in the datasheets. I wanted to make doubly sure that the 7450 and 7457 were actually pin-compatible, and to make sure that those pins match up with the signals in the schematic. So in each cell, it lists the name of the pin according to the datasheets for the 7450, 7455, and 7457, and the last line is the signal name on the PCB, according to the schematic. Cells with a red outline indicate pins that didn't match up 100%. (But from what I can tell, should be fine.) I find it a lot easier to read than the pinout/signal list in the datasheets.
The second file is an Omnioutliner file for the PLL configurations, showing the bus multiplier in the leftmost column, with the other columns showing what the PLL config is for the 7450, 7457, and according to the iMac schematic, respectively. Made it a lot easier to see the differences in PLL configs between the 7450 and the 7457, showing that for the most part they line up. I'm uploading it here as a PDF because maybe not everyone has Omnioutliner.
Also made a Soulver file to run some numbers, but I'm not going to upload that. It's just a little utility for me to figure out power consumption, using available data from the datasheets. (Imagine that! Data in a datasheet!) I was able to use it, though, to determine that I will need a beefier power supply, especially with the L3 cache. Basically, with everything configured the way I want, I'll be pulling ≈12.2 more watts than the original configuration. (I love when electrical work gets all mathy.
) So I found someone who was parting out their USB 2.0 iMac G4 and bought the power supply off of them for $20. 160W, which is 30 more than what the iMac currently has, which should cover the difference with more to spare.Of course, 30 more watts means more heat, so the exhaust fan is definitely going to need to be beefier. I'm still looking into that. Also, the 160W PSU has a 16-pin molex connector, rather than the 14-pin on my iMac. Not an deal-breaker, though; all the signals are the same, with the addition of an extra pin going to ground and an extra pin going to FireWire power directly, which is an interesting quirk of the USB 2.0 iMac. But if you took those pins off, then the pinout is the same as the 14-pin molex. So that should be pretty easy to adapt.
All that said, I decided that I'm going to work on the compacts first before I get to the iMac. They definitely need more love at the moment to get to full working order.
re4mat
Well-known member
Hello! @re4mat I just discovered this post! It's been many years, but I recently did the CPU SWAP to an iMac G4 800MHz, and I would like to add the L3 cache. How did the project progress?
I have not made any modifications to either the power supply or the Vcore regulator, except adding a LowESR capacitor next to the Vcore capacitors.
Here my experience, in Spanish, since I live in Spain.
https://rosysumenteinquieta.blogspot.com/2023/12/imac-g4-800-cpu-swap.html
P.S. It seems clear that the NOL3Cache Resistors on page 4 must be eliminated, but I am not so clear about the ones on page 22 and 24, one seems to give a power signal and the others go to a development connector.
I have not made any modifications to either the power supply or the Vcore regulator, except adding a LowESR capacitor next to the Vcore capacitors.
Here my experience, in Spanish, since I live in Spain.
https://rosysumenteinquieta.blogspot.com/2023/12/imac-g4-800-cpu-swap.html
P.S. It seems clear that the NOL3Cache Resistors on page 4 must be eliminated, but I am not so clear about the ones on page 22 and 24, one seems to give a power signal and the others go to a development connector.
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