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Clocking the 6400's Mother Board

This page has all the info I have collected on changing the mother boards speed of 6400's
Disclaimer: Try these changes at your own risk. The 6400 Zone will not be held responsible for damage to your system
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Over Clocked 6400 mother board!: Here is a letter from Thorsten who managed to bump up the mother board clock speed from 40Mhz to 48Mhz which in turn made the CPU run at 216Mhz. I have asked for more info on how he did it. Thanks Thorsten.

UPDATE: He sent me a reply and here it is. I must mention that I made a mistake on the CPU speed. He actually had to lower the CPU speed to 180Mhz then it got increased to 216Mhz with the bus speed change. If he didn't lower it then it would run at about 240Mhz and lock up.

Over Clocked 6400 MB update: I just got the web address to the page that has the info on how to make this change. remember that when you change the mother board speed that your CPU will also increase. You may have to decrease the CPU before increasing the Mother Board or risk instant crashes on boot.

Here is a picture from the Clock Chipping Home page of a 5400 mother board (identical to the 6400) and where the change needs to be made. I will have more info posted here soon.

5400 Mother Board image

Update 1/29/1999: I don't know if I made it clear enough before so here goes. With the MB clocked to 50Mhz your CPU will run at either 225Mhz for the 6400/180 or 250Mhz for the 6400/200. You have to remember the CPU to MB multiplier. The 6400/180 has a 4.5x and the 6400/200 has a 5x. This is how it works. with a 40Mhz bus times 4.5 you get 180Mhz CPU.

Both 225Mhz and the 250Mz are well beyond the distance the 603e we have can handle. I only recommended a 180 goto 200 and a 200 goto 220. If you change the MB speed a lot without lowering the CPU multiplier then you will crash. you could probably goto a 45Mhz bus with no issue as the 6400/180 will become 202Mhz and the 6400/200 will become 225Mhz. Both slightly more than I suggested but I think it should work fine.

I beleive the G3 will work but the speed cannot be predicted. For the stock 40Mhz bus it runs at 240Mhz. But on the 6500 with a 50Mhz bus it runs at 225Mhz. It actually runs slower because it has to change its multiplier or it would run at 300Mhz and fail instantly. So I don't know what speed it will pick for MB speeds inbetween 40 and 50Mhz.

I hope this helps.

Update 2/6/1999 Another 6400 MB upgrade success: I recieved this letter from Dave Barton who has changed his mother board speed from 40Mhz to 48Mhz which also took his CPU from 180Mhz to 216Mhz. Nice improvment for just one change. Thanks for the info Dave.

6400 with a full 50Mhz bus!: Thorsten did it. He found a 50Mhz crystal and now is running with a 50Mhz bus and a 225Mhz CPU. He is also willing to sell the left over 50Mhz crystals he has. Thanks Thorsten!

2/12/1999 50Mhz bus maybe too fast for the 6400!: Thorsten wrote to let me know that he has reduced his MB back to 48Mhz due to system errors. His mother board was pushed passed its limit. A cooling fan for the entire system (not just the CPU) may be needed?

Here are a few pictures Thorsten sent me, Thanks Thorsten.

6400 MB layout with crystal

6400 MB closeup of crystal

DigiKey part number for MB crystal: David replied to my request for more info on his MB clocking experiences. Thanks David.

4/23/1999 Another 6400 MB clocked to 50Mhz: Ed sends word that he has a letter posted on Marcs web site and it has a lot of detail on different speeds of MB crystals tested. Thanks Ed.

5/27/1999 The master of 5400/5500 clocking!: I recieved this letter from Joey who has done some intense testing on clocking the CPU and mother board of 5400 and 5500 series Macs. I assume his findings may also work for 6400's and 6500's since they use the same mother boards. Also read the part about using a G3 upgrade with a clocked mother board. Seems we can get some extra speed out of these cards after all! Thanks Joey. Click here to email him for more details.

1/26/2001 More mother board clocking results: McKinney was kind enough to send me some info on his mother board clocking experiences. Thanks McKinney. He has a Sonnet G3 which got a boost by the MB clocking.

[Here is a follow up to my motherboard clocking experimenting. I found a 46 mhz crystal (since the 48 was a no go) and here are my results. I am attaching a screenshot of my desktop that has Macbench and Metronome open so you can see what the computer is running at. I have not done a lot of heavy use to test stability but I have used IE, Entourage, Photoshop 5.5 and all seems to work fine with no adverse temperature or stability problems. I will update you if I run into problems. I am also attaching a screenshot with my system profiler

I got the crystal through the vendor listed on your website (DigiTech). I used the Sonnet Clocker to make 6x, 6.5x,7x,7.5x and of course the 8x extension I was using. The 8x will not run and freezes but I am using the 7.5x to get 345mhz. I have tried using the lower speed multipiers to alleviate the sound issue but it does not seem to help. I have used the G3 cache control to slow the cache down, I have used the PCI timing extension, and ATI sound catalyst and none seem to help. :(

McKinney's Sonnet Metronome results

McKinney's MacBench 5 Sonnet test scores

4/21/2001 6400 mother board clocking with a Sonnet G3 installed: Ed sent me some info and a link to his site where he has info on his experiments on clocking the MB in his 6400 to see how it affects the Sonnet L2 G3 he owns. Very interesting reading for tinkerers :) Thanks Ed.

[Hi Tom
I just wanted to pass on a little info. I'm in the process of writing it up now and will post it at my "Clocking the Macintosh <http://www.mcn.net/~nye/> " site as soon as its ready. I still have the motherboard of my 6400/180 <http://www.mcn.net/~nye/Results/Index.html> running at 50 MHz and until I installed the Sonnet Crescendo-L2 G3 350/175/1M <http://www.sonnettech.com> , my 603e processor was running a flawless 225 MHz. Since I only need the 603 to boot, I slowed it down from 4.5x (225 MHz) to 3.5x (175 MHz) to reduce heat in the case. I had 40 MHz, 45 MHz, and 48 MHz crystals ready just in case. I thought with the 50 MHz bus it would be treated as a 6500 and boot at 350 MHz instead of 320 MHz. As soon as it booted I opened the Metronome and was pleasantly surprised! The processor speed at 400 MHz with secondary cache at 200 MHz. I still have my Quick Change Block <http://www.mcn.net/~nye/Block/Index.html> and crystal socket installed so I tried several other frequency crystals and the speed followed proportional to the crystal. Sonnet must use the gestalt ID and not the bus speed to set the card speed. I ran some processor intensive tests to check stability and temperature, at 400 MHz and have not had any problems so far! Knock on wood!!!! I'll post some benchmarks and details as soon as I can.
Ed N]

7/21/2001 6400 motherboard over clocked!: McKinney sends word on his experiences on over clocking his 6400's motherboard.

[Hello everyone. I am finally moving on to a new machine and just wanted to let you know why. After "experimenting" with every upgrade that could ever work with the 6400, I finally pushed it too far. I clocked my motherboard bus to 46 mhz and overclocked my G3 Sonnet to 345mhz. This set up worked fantastic until I started having problems with the system booting up. I initially thought it was a cooling problem but after adding fans which keep the G3 cool (39c) I narrowed it down to the motherboard. To make a long story short...my advice is to leave the motherboard alone. I used the Sonnet Clocker prior to messing with the motherboard and had ZERO problems running it at 320mhz.
I have finally purchased a new computer (a new 500mhz G4 Server, 36 gb SCSI 160/10,000rpm HD, DVD, 512mb Ram, SCSI card ,gigabit ethernet from Small Dog for $1700). All my 6400 upgrades are going to my son's Performa 6360. It will make a 6 year old a damn fine machine!!!]

And later he sent this

[Tom, It did get to the point where the computer would lock up at any sign of "work" but I installed two 2" fans that kept the G3 running cool (39c). I suppose the motherboard has a heat issue because when I let it cool off for 10-15min it will restart. The only other quirky thing is that if I install software that requires a restart the machine will not reboot. I have not received my G4 yet so I am still using the 6400 and it has been on all day. It will not do any amount of hard work (videos, encoding mp3's, unstuffing a large file or games etc )without locking up. Prior to messing with the motherboard the machine would run 24/7 and memory was the only limitation. Again my advice is to leave the motherboard alone and try not to "hotrod" the 6400 to it's death. I do however think the Sonnet G3/1mb runs flawless at 320mhz (courtesy of the Sonnet Clocker). All my goodies (Ati Orion, 136mb memory,8.4g HD, comm slot II ethernet card and the Sonnet G3) are going to be transplanted into my son's 6360. Can't wait to get my G4....hopefully it will last me as long as my 6400 did (5 1/2 years!!). Can you imagine using a 5 1/2 year old Wintel machine?? NOT!! :)]

This is one reason why clocking any component on your computer should always be considered as taking a risk and you could permanently ruin your system. As always, clock at your own risk!

11/18/2001 6400 Mother Board overclocking info from Thierry: Thierry sent me a lot of good info on his mother board clocking experiments. Thanks Thierry! It is rather large so click here to read the entire letter.

2/9/2002 Overclocked mother board may have killed this users 6400?: HB McKinney sends word that his 6400 died and he believes that overclocking the mother board may have done it! Whether that is the cause or not, overclocking anything is always a risk and this could happen to you. Thanks HB McKinney.

  • [My 6400 finally died! I have been posting to this site for several years now and just wanted to give an update. I have one of those "maxed out 6400's" with 136mb, 20gb hd, 10/100t ethernet, ATI Orion (yuk), Sonnet G3 300 running at 325, USB card, external CDRW, SCanner, Zip, 3 piece speaker system . It has been a great machine but it finally died. My advice to anyone who truly wants a stable and healthy system is to avoid tampering with the motherboard. I overclocked the motherboard to 46mhz and while that lasted almost a year I am sure it is the cause of it's death. I transferred the upgrades to a 6360 so it lives on in spirit!

    My main computer now is a G4 running OS X. Having made the jump to a new machine and OS X I just want to let everyone know that it is worth it. OS X is fun and stability is unbelievable. iPhoto, iMovie, Office, iDVD are all incredible and I am now confident that Apple has a winner with OS X. People are generally afraid of change....but this time change is good!]

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This page last updated 4/23/2003