500 Mhz G3 iMac rev E to a G4

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ken_the_stp's picture
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I have seen on the web that there is a company that I could mail my logic board to and they would remove the L2 cash and CPU and replace them with a G4 500mhz and 1meg of L2 cash.

This has made me very inquisitive!

I am wondering if anyone can answer theses questions.

is that it all I have to do is swap the chip and the cash out?

the logic board can be clocked to 1ghz. with this in mind would it be feasible to place a 1ghz G4 on the board with this clock setting.

will changing this clock setting be too taxing for other parts of the board. and what other effects besides changing the clock speed of the cpu be.

Thanks

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The logic board can be closed

The logic board can be closed at 100 MHz, switching to a G4 will not change that. Instead you just use a higher multiplier. However, the old 7400's that they use in those upgrades are not available in speed grades higher than 550MHz.

Oh, and it's spelled "cache".

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ken_the_stp's picture
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I don't suppose

I don't suppose there is anything else that can be modified on the board to allow for the use of a different G4.

would the use of a 900mhz 750FX be at all possable.

Thanks a whole lot
=)

o yes cache um hmm

O and BTW where could I get my hands on the cache chips and cpu? and for how much?

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hey how can you overclock a 5

hey how can you overclock a 500 mhz imac board! i got one! and i wanna over clock! Cool Mac

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martakz's picture
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With difficulty and a solderi

With difficulty and a soldering iron...

Looking for link...

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Now using x86 machines. Bye bye iMac266 (Strawberry), G3 1400 and the G3 IIsi.

ken_the_stp's picture
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here's how

PUT A FAN ON THE CPU!!! in the case(somehow) too.

http://www.bekkoame.ne.jp/~t-imai/imacde1.html

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Not really, no

G4s after the 7410 aren't bus-, pin- or voltage-compatible, so it's essentially impossible to use them.

The 750FX or 750GX is (kind of) tantalizingly close to the realm of possibility, given that there's a company that markets 800MHz 750GX upgrades for the Pismo, which is based on the same UniNorth/KeyLargo architecture as the original 500MHz iMac (both use the 750 processor; since this is not pin-compatible with the 750GX, they presumably manufacture their own processor daughtercards).

Unfortunately, since the processor in this iMac is (to the best of my knowledge) soldered to the logic board, you can't really put the extra circuitry required for the 750GX anywhere. You'd have to replace the regulators for the processor core (since it runs at a much lower voltage than the original G3), and have a custom board manufactured that you'd be able to solder a 750GX to one side of, and attach BGA balls to the other, so you could solder the whole thing down in place of the original processor. The problem is, this would increase the distance between the processor core and its bypass capacitors, which could potentially lead to system instability. Also, it would be extremely difficult to design the adapter board in such a way that it didn't cause problems due to varying signal lengths or added capacitances and impedances. The cost would be several hundred dollars to have the board manufactured, and vastly more to have it assembled (forget about doing it yourself, you need specialized equipment to work with BGAs). Oh -- and you can generally only buy 750GX chips in pallets of 44.

Later iMacs (including a couple more 500MHz models) are based on the Pangea ASIC, and use a 750CX processor, which is bus-compatible with the 750, 750FX/GX, and 7400/7410, but unfortunately isn't pin-compatible or voltage-compatible. Same limitations apply as above, but in this case, you can't even have it replaced with a 7400.

All things considered, I suggest paying for the company to do the upgrade. It'll be cheaper.

As for your last question, hopefully it has been rendered redundant, but if you still want to know: this company supposedly sells individual processors. I'm not sure if they sell to hobbyists, and they don't have any prices listed -- you have to ask for a quote.

ken_the_stp's picture
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IBM 750L pin and voltage compatible with the mot 750?

This particular board has a 750 in it.

IBM has and adaptor card for the 750FX/GX to a CX or a 750L
http://www-306.ibm.com/chips/techlib/techlib.nsf/techdocs/CF001FEA750CB1DA87256E3F005EED44/$file/750FX_Adder_Card_apnote-12-17-03.pdfprovieded I can hire some firm to do the BGA solder(http://www.technowarehousellc.com/g4upforslloi.html they do the solder for G4 upgrades for this box perhaps they would do this job for me =) )

considering that the 750L is not a mot cpu I am not sure if this card will work for this application.

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Yes, it is

The 750L is, to the best of my knowledge, a drop-in replacement for the MPC/XPC750. There are, however, 2 issues with the IBM card:
1. It doesn't have on-board regulators, so you'd still need to find and replace the iMac's ones (probably not too difficult)
2. IBM state that it's for development/sample purposes only.

So, unless you or someone you know have a very cosy relationship with an IBM sales rep, you'd probably have a hard time convincing them to give you one. Also, being a development part, it's probably obscenely expensive (think 4 figures).

However, another way of looking at it would be that the concerns regarding an adapter board I outlined in my previous post are obviously not major problems, so it's certainly possible to build adapters. And, with the large number of companies offering up to 8-layer custom PCB fabrication for reasonable prices, it could even be within the financial reach of a somewhat obsessive, hard-headed and well-heeled hobbyist. I've actually done preliminary research for a similar project, but I put it on hold while I tried to get information on the trace length and bypass capacitor issues. Since they don't appear to be as significant as I originally thought, maybe there's some sense in looking deeper into it.

Basically, the conclusion I came to was that fabrication of a custom 6-layer board would cost in the region of $400 for 5 or 10 units, not including the attachment of BGA balls to the underside or component and assembly costs. If you could buy individual processors, a 750GX (better than the 750FX due to 1MB of on-chip L2 cache running 1:1 with the core, and thus the absence of need to connect the L2 signals) at 800MHz would probably cost in the region of $200-250. Assembly would probably run to at least another couple of hundred. So, for little more than the cost of a brand-new eMac, you could have one of the fastest G3 iMacs around Smile .

Anyway -- I'd love to see it happen, because I could really use adapter boards like that, but from what I can see of your situation it just doesn't make much financial sense to spend up to several hundred dollars and a significant chunk of your time on such an old computer. But, if you're willing to spend the money, I don't see much reason why it can't be done.

ken_the_stp's picture
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Ponder Ponder

At the moment I have been pondering this possibility.
soldering pin's to the bottom of the 750GX cpu, ind a circuit board that has easily accessible paths to to pins, put the conversion circuitry on a different board solder them together, use several lines of ribbon cable to connect that board to the logic board, device a mount problem a some peaces of metal connected to logic board, and completely understand trace length issues and as I am almost cretin that I will need to find a way to compensate for that much distance between the core and the cpu.

I believe with research this would be a viable method of implementing this.

In the mean time I will start thinking up the case that this creation will go in.

BTW dose anyone where I can find advanced info on the mot 750 cpu. I do not seem to be able to find anything while navigating mot's web page.

Thanks for the posts everyone! Cool Mac

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Trace length is the biggest issue

I don't think you'd get it running stably over ribbon cable unless you interfaced it via some sort of HyperTransport-like LVDS system. There are a couple of issues: firstly, if you have signal path that long, the propagation delay will be greatly increased; secondly, at the sort of speeds the G3s run at, you'd need termination for any trace longer than a few centimetres or so. Better to stick with the adapter board and minimize trace length.

All information for the MPC/XPC750 will be on Freescale's site, under "embedded processors".

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Speed Bump on TiBook 800

I'd like a small bump in speed- maybe to 867 or 900 from my stock 800 MHz if possible. Is there anyone out there that has done this successfully on an 800 MHz TiBook? I'm considering trying some of the video acceleration software/shareware out there to see if that works and if it does, then I'll be happy.

E. G., I've been able to play C.O.D. effectively on my machine, but in the very complex scenarios the frames are jerky to very jerky even with the least demanding settings. So- I'd like to hear if any of you have had luck in increasing the performance of your TiBooks just a bit.

Or could I be nuts for even wanting to try to do this? I've built my own scientific instruments (that actually worked, didn't explode very often and even gave me publishable results) so I'm not a complete klutz with a soldering iron, but I wouldn't say I was a god at it.

I've taken a job with an all WinTel shop and now I don't have the opportunity to write grants for new toys (or get them from the Dean as part of my sinecure anymore) so I'd like my TiBook laptop to zip along a bit faster rather than cough up for the last non-intel Macs.