Blue G3 Bus Clocking

[cobalt60]

I know the information is out there, but I am having trouble finding it...

What are the jumper settings for changing the bus speed on Blue & White G3s?

 

[Phipli]

I know the information is out there, but I am having trouble finding it...

What are the jumper settings for changing the bus speed on Blue & White G3s?

Here you go : https://web.archive.org/web/20080509154006/http://www.xlr8yourmac.com/G3-ZONE/yosemite/OC.html

 

[cobalt60]

Thanks very much.
Attaching the info here:

• 6,7,9 = 66MHz
• 5,6,7,8,9 = 90MHz
• 5,6,7,8 = 94.5MHz
• 5,6,8,9 = 100MHz
• 5,6,8 = 116.3MHz [unstable in 1 test system - 38.75Mhz PCI bus]
• 5,6,9,10 = 120MHz [stable in 1 test system - 30MHz PCI bus]
• 70MHz & 105MHz settings not found

 

[croissantking]

Other than running the PCI bus at weird speeds like 38.75MHz, what factors limit stable bus overclocking? Is it the components or also the board design too?

My old G3 MT used to run stable at a 83MHz bus, but its XPC106 chipset (Heathrow? Grackle?) was rated as such. My current G3 DT’s chipset is only rated to 66MHz, so I’m not sure how it would fare.

 

[Phipli]

Other than running the PCI bus at weird speeds like 38.75MHz, what factors limit stable bus overclocking? Is it the components or also the board design too?

My old G3 MT used to run stable at a 83MHz bus, but its XPC106 chipset (Heathrow? Grackle?) was rated as such. My current G3 DT’s chipset is only rated to 66MHz, so I’m not sure how it would fare.

The default RAM rating is 66MHz, so you would do well to upgrade that to PC100 or PC133 if you haven't already. But overall, you're pushing everything connected to the bus harder, so the unhelpful answer is "loads of things".

It just depends what gives up first and varies between every indicidual computer. Not a very helpful answer sorry.

 

[croissantking]

My RAM is all PC100 or above. I don’t think I’ve come across many, or any PC-66 DIMMs; certainly none that are labelled as such. I get the impression that the industry went to PC-100 very quickly.

I have a spare XPC chip rated to 100MHz so I’ll swap it in if I ever learn how to do BGA soldering.

 

[cobalt60]

Are the XPC chips straight swaps from the Blue G3? Or what are the sources for these chips? Do they need any sort of programming before being used? Is the XPC chip the one that has the PLL config to set the bus speed?

Way back in the day, I got my Sawtooth G4 running with a 120MHz bus, but it would not run at 133MHz with PC133 memory. The error code I believe indicated a memory failure. Now I am wondering if that machine has a similar (or other) chip I could replace with one from a Digital Audio or Quicksilver.

 

[croissantking]

Are the XPC chips straight swaps from the Blue G3? Or what are the sources for these chips? Do they need any sort of programming before being used? Is the XPC chip the one that has the PLL config to set the bus speed?

I am pretty sure they are a straight swap, I recently read about someone who had done this successfully.

Way back in the day, I got my Sawtooth G4 running with a 120MHz bus, but it would not run at 133MHz with PC133 memory. The error code I believe indicated a memory failure. Now I am wondering if that machine has a similar (or other) chip I could replace with one from a Digital Audio or Quicksilver.

Yeah, 133MHz is probably too much of a push. Was it stable at 120?

I’m not sure that the Sawtooth uses the XPC chip, I think the chipset changed with the debut of the AGP G4s.

 

[cobalt60]

Was it stable at 120?

Was 100% stable. The link in my sig is the article I wrote about it. Was before my professional career as a tech, so, some things I say there are a bit noobish, but still good info in there.

 

[cobalt60]

what factors limit stable bus overclocking?

Not sure how much it comes into play, but figure its worth mentioning. The CPUs themselves have a FSB rating.

66MHz - 750, 755
100MHz - 750L, 750CX
133MHz - 750CXe
166MHz - 750FX, 750FL
200MHz - 750GX, 750GL