PowerMac G3 Minitower - Identifying a 333 MHz Motherboard

The A, B, and C, after the logic board number denote a logic board revision, not a processor speed. You want a Rev b or C--the Rev A supports only only one device per ATA cable whereas the B and C models support two--nice fo addin extra drives.

Otherwise the Beige G3 logic board as a part should be fairly generic. The G3 processor is socketed so it is easy to change out the processor. One of my Beige G3s (both are rev C) started as a 300mHz machine and I upgraded the processor to 500mHz. You can simply install a faster processor in the processor socket to get a faster Mac--no logic board swaps are required.

Other factors are controlled by a single processor jumper block. See this diagram:

Apple made it easy with one basic board that could be fitted with different processor speeds using these jumpers. The setting for the jumper blocks are here:

https://web.archive.org/web/20000505093026/http://www.bekkoame.or.jp/~t-imai/g3a e1.html

More overclocking info here:

http://lowendmac.com/1997/overclocking-beige-power-mac-g3/

People used to get in trouble trying to change the default 67mhz bus speed and PCI bus to something higher, especially of you had a PCI card of some sort installed. However you can leave those speeds alone and still do some minor adjusting to only the CPU clocking jumpers.

Apple had factory jumper block caps that set all the parameters for one model simultaneously. Overclockers remove the one-piece factory cap and use small jumpers similar to those used on ATA hard drives (2mm as I recall), or simply jump the exposed connectors in the factory block with a short bit of gold wire.

It's been a long time since I was inside my two Beige Beasts but, if you have other questions, I can possibly jog my geriatric memory of these things.

Follow-up regarding about markings on processors: I found the original Apple Motorola G3/300 ZIF processor card I removed from one of my G3s during upgrading. The core is marked (silkscreened) "XPC750 PRX300PA" and a paper sticker on the supporting mini-board reads "XPC750HIP300CJ."

So at least it appears that Motorola included the processor speed in the part number. IBM also made G3 processors and the one in my upgraded G3 is an IBM. Unfortunately I can't get to the stored unit right now to examine the processor card for its labeling.

If looking for an upgrade processor card instead of a standard one pulled during an upgrade, look for Sonnet Encore/ZIF (discontinued but maybe still around on eBay). I recall their being made in 400 and 500mHz speeds. They are easy to install as long as you remember to get out the magnifying glass and, with a wooden toothpick, remove leftover bits of the anti-static packing foam from every one of the 288 contact pins! I missed one and the computer would not start until I removed the new processor and evicted one offending and minuscule bit of foam.

Thanks, RB, I'm glad those old days inside the Beige Beast business proved helpful.

You mentioned 333 mhz models--another tidbit: Most 333's shipped with an Ultra-SCSI 2 9GB hard drive connected to a PCI U-SCSI 2 adaptor card. One of mine is that config. It did not use the slower logic board SCSI connector. It was very fast for its time, but came with a serious caveat. The U-SCSI 2 card had one external port not used (the internal SCSI drive was connected to an interior port on the PCI card). The exterior port was covered with a bit of paper and that was supposed to prevent people from using it. It didn't, some people removed the paper and some fried SCSI cards and logic boards ensued. If you get a 333 and it has the SCSI, leave the card's external SCSI port alone.

BTW, about your precaution regarding the anti-static packaging bits on the processor pins . . . . Why couldn't you blow it clean with compressed air?

Excellent question. Sonnet used some odd sort of foam whose material was somewhat sticky in nature. Everyone had this issue so, from these forums and others, I knew going in that canned air would not work--the offending bits were just stuck too well for air in a can to move.

I probably spend way to much in upgrades on my Beige minitowers but I can't put a price on what I learned about computers in general, PPC Macs specifically, and how to work on computers. They were the ultimate "get under the hood" Mac.

"Does this mean that if I find a motherboard with Apple Part No. 820-0991-B, that it will be a 333 MHz motherboard, or there something else involved in the equation?"

No, the motherboard part number indicates nothing about processor speed. An 820-0991-B motherboard could have any processor installed in it at this point. Back when the computer was new, if it were a Build-to-Order unit manufactured in mid-to-late-1998, processor speeds varied. The stock CPUs in these G3s shipped with a designated color-coded jumper block (233 MHz: red, 266 MHz: white, 300 MHz: black, and 333 MHz: green). One of the easiest ways to determine processor speed on an unmodified, bare motherboard would be to check the color of the jumper block.

"If I replace the 266 motherboard with one out of a 333, is that all that is necessary to make it a 333 machine?"

Yes, but check the jumper block color. Regardless of the processor speed, the incorrect jumper block can slow it down to the speed I've indicated above. Also, there's a power supply jumper (J28) on the motherboard, close to the back near the PCI card slots. Depending on whether you have the desktop or mini-tower model, the jumper may not be set correctly for your computer. For use in a desktop, the jumper should be set to "MAC." For use in a mini-tower, the jumper should be set to "PS/2." An incorrect setting will prevent the computer from powering up, and possibly give you the impression that the motherboard is defective.

The first two motherboards (820-0864-A and 820-0864-B) will have the ATI 3D Rage II +DVD graphics chip. The third revision (820-0991-A) has the ATI Rage Pro graphics chip, and the fourth revision (820-0991-B) has the ATI Rage Pro Turbo graphics chip. The support for master/slave configuration of dual drives on a single ATA channel is controlled solely by the installed ROM card and not by the motherboard version. The original ROM card ($77D.40F2) had this restriction, but the two subsequent revisions ($77D.45F1 and $77D.45F2) didn't. That's why some owners of late-1997 or very early-1998 beige G3s replaced the original ROM card with either of the two latter versions. I did that with one of mine - a 300 MHz desktop model. Concern about the onboard graphics chip was a non-issue, because I installed ATI Radeon 7000 graphics cards in all of my G3s.

If a beige G3 shipped with the DVD drive, it would also have the A/V personality card with the onboard MPEG decoder chip for watching DVD movies. The processor speed would be the 300 or 333 MHz version. The earliest versions of the "Apple DVD Player" program depended on a hardware-based decoding scheme, so a fast processor was needed and the display had to be connected to the onboard DB-15 monitor port for the setup to work. The stock SGRAM was 2 MBs, but could be upgraded to 4 or 6 MBs. By the late-90s, that was considered incredibly small. Having a Radeon 7000 graphics card with 32 MBs of DDR memory in my G3s, I didn't want to watch movies on a display connected to a slower onboard GPU. Running a modified version of the "Apple DVD Player" program that used software decoding, I was able to watch DVD movies on a display connected to the Radeon card. On the 266 MHz G3s, it could lag at times, so performance was definitely better with the 300 or 333 MHz processors.