Guide to changing MDD bus speed / CPU upgrade

harrymatic

macrumors 6502
Original poster
Dec 30, 2013
331
20
United Kingdom
I mentioned last week that I ordered a dual 1.33 GHz CPU module for my MDD G4. The new CPU was pulled from a G4 Xserve – it has 2MB of L3 and requires a 167 MHz frontside bus to work at its full clock speed. It arrived today so I thought I’d document the upgrade process for anybody else wanting to upgrade their MDD G4.

This particular G4 happens to have the slower 133 MHz FSB – it originally shipped with a single 1 GHz module and is one of the FW800 models. Fortunately, it is fairly simple to change the bus speed on the MDD boards – you just need to remove a resistor on the underside of the board.

1. Remove all cards, cables and the single screw securing the logic board to the case (it’s near the little fan in the door). I also removed the backup battery. Slide the logic board away from the back of the case and remove it.

2. Locate and remove the resistor marked R676 on the underside of the board – it’s near the heatsink under the CPU area. (see photos) You’ll need a fine pencil-tip soldering iron. Make sure that the removed resistor doesn’t get lost somewhere on the board! I didn’t find this too difficult as I do a lot of work with electronics, but if you don’t have experience with SMD components, practice loads on some old PCBs first.

3. Reinstall all components back in the case and reattach any cables. Remember to reapply thermal paste on the CPU module before putting the heatsink back on.

This upgrade gave me a huge increase in system performance. There is now absolutely no slowdown anywhere in the Leopard UI. YouView can now play 720p HD videos quite happily, Flash Player is now able to play full-framerate full-screen SD video in all of the websites I tried it with. Games are now running so smooth, it's just great. :D
 

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eyoungren

macrumors Core
Aug 31, 2011
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OK. So, I have to ask because I'm clueless about all this bus stuff. Is it possible to speed up the bus on my G4 Quicksilver?

I know it's not the MDD you mention in this thread, but if there's a way I'd sure like to find out. My QS started life as a 733mhz single processor. But right now it's running a Giga Designs 7447A G4 dual at 1.73Ghz.

If there's no way to speed up the bus, that's fine. Just wondered.
 

Goftrey

macrumors 68000
May 20, 2011
1,844
70
Wales, UK
Great post. I'm sure it'll get a lot of attention in the future - certainly beats out people digging through the archives looking for that pretty vague guide that's written up in French (AFAIK that's the only other proper 'guide' out there for doing this).

I was going to do the same to my DP 867MHz, but was able to get my mitts on a DP 1.42GHz for an insanely good price literally days after picking the 867 up (the 1.42 had a blown PSU, simply swapped the one out for the other et voila).
 

harrymatic

macrumors 6502
Original poster
Dec 30, 2013
331
20
United Kingdom
OK. So, I have to ask because I'm clueless about all this bus stuff. Is it possible to speed up the bus on my G4 Quicksilver?

I know it's not the MDD you mention in this thread, but if there's a way I'd sure like to find out. My QS started life as a 733mhz single processor. But right now it's running a Giga Designs 7447A G4 dual at 1.73Ghz.

If there's no way to speed up the bus, that's fine. Just wondered.
I'll have a look and see what I can dig up - I definitely recall people changing the FSB speed on the old Sawtooth G4s back in the day - there was even a place on the logic board where you could solder in some DIP switches to set it to whatever you liked.
 

archtopshop

macrumors regular
Dec 13, 2011
206
1
OK. So, I have to ask because I'm clueless about all this bus stuff. Is it possible to speed up the bus on my G4 Quicksilver?

I know it's not the MDD you mention in this thread, but if there's a way I'd sure like to find out. My QS started life as a 733mhz single processor. But right now it's running a Giga Designs 7447A G4 dual at 1.73Ghz.

If there's no way to speed up the bus, that's fine. Just wondered.
The only concept needed to understand is your processor is set to run at a multiple of your bus speed.

In your case, your processor is running at 1730 MHz. If I remember correctly, your bus speed is 133MHz. 1730 divided by 133 is 13. So, your processor is set to run at 13 times the bus speed.

If you increase the bus speed to 167MHz, then 167MHz*13=2173MHz, or 2.17GHz. Your processor probably won't work at that high of speed. So, you will need to adjust the multiple down until you reach a speed at which your processor will work at the higher bus speed.

I hope this helps.
 

eyoungren

macrumors Core
Aug 31, 2011
21,264
13,115
ten-zero-eleven-zero-zero by zero-two
The only concept needed to understand is your processor is set to run at a multiple of your bus speed.

In your case, your processor is running at 1730 MHz. If I remember correctly, your bus speed is 133MHz. 1730 divided by 133 is 13. So, your processor is set to run at 13 times the bus speed.

If you increase the bus speed to 167MHz, then 167MHz*13=2173MHz, or 2.17GHz. Your processor probably won't work at that high of speed. So, you will need to adjust the multiple down until you reach a speed at which your processor will work at the higher bus speed.

I hope this helps.
Well, the CPUs actually have settings up to 2.0GHZ. I can get the Mac to boot at 2.0Ghz but it goes direct to Open Firmware and then I have to boot it from there. At which point it will freeze at any given point. If I can increase the bus speed maybe I can then increase the CPU speed? It'll also run at 1.8Ghz and boot normally, but I get freezes. So, I settled at 1.73GHZ with 1.65voltage.
 

archtopshop

macrumors regular
Dec 13, 2011
206
1
Well, the CPUs actually have settings up to 2.0GHZ. I can get the Mac to boot at 2.0Ghz but it goes direct to Open Firmware and then I have to boot it from there. At which point it will freeze at any given point. If I can increase the bus speed maybe I can then increase the CPU speed? It'll also run at 1.8Ghz and boot normally, but I get freezes. So, I settled at 1.73GHZ with 1.65voltage.
If it doesn't run stable at 1.8GHz with 133MHz bus speed, then I don't think it will run 1.8GHz with the bus at 167MHz either. Adding more cooling might help. That would be my first step to try.

Adjusting the voltages is something I never fooled around with, so I don't know how that would affect it.

----------

I mentioned last week that I ordered a dual 1.33 GHz CPU module for my MDD G4. The new CPU was pulled from a G4 Xserve – it has 2MB of L3 and requires a 166 MHz frontside bus to work at its full clock speed. It arrived today so I thought I’d document the upgrade process for anybody else wanting to upgrade their MDD G4.

This particular G4 happens to have the slower 133 MHz FSB – it originally shipped with a single 1 GHz module and is one of the FW800 models. Fortunately, it is fairly simple to change the bus speed on the MDD boards – you just need to remove a resistor on the underside of the board.

1. Remove all cards, cables and the single screw securing the logic board to the case (it’s near the little fan in the door). I also removed the backup battery. Slide the logic board away from the back of the case and remove it.

2. Locate and remove the resistor marked R676 on the underside of the board – it’s near the heatsink under the CPU area. (see photos) You’ll need a fine pencil-tip soldering iron. Make sure that the removed resistor doesn’t get lost somewhere on the board! I didn’t find this too difficult as I do a lot of work with electronics, but if you don’t have experience with SMD components, practice loads on some old PCBs first.

3. Reinstall all components back in the case and reattach any cables. Remember to reapply thermal paste on the CPU module before putting the heatsink back on.

This upgrade gave me a huge increase in system performance. There is now absolutely no slowdown anywhere in the Leopard UI. YouView can now play 720p HD videos quite happily, Flash Player is now able to play full-framerate full-screen SD video in all of the websites I tried it with. Games are now running so smooth, it's just great. :D
Thanks for this post. Good stuff.:D
 

eyoungren

macrumors Core
Aug 31, 2011
21,264
13,115
ten-zero-eleven-zero-zero by zero-two
If it doesn't run stable at 1.8GHz with 133MHz bus speed, then I don't think it will run 1.8GHz with the bus at 167MHz either. Adding more cooling might help. That would be my first step to try.

Adjusting the voltages is something I never fooled around with, so I don't know how that would affect it.
Well, at 1.5v (the default) all I get is a black screen with the CPUs set on 2.0Ghz. So, adjusting the voltage to 1.65v let it boot, even though I have the issues.

I've already added back the original fan that was not there when I got this machine because it was unnecessary in the previous upgrade. And the processors themselves came with two small fans on the heat sink. I suppose I could try an additional fan and see what happens, but I'm not sure if heat is the issue, versus just the processors. Something to try though. Thanks!
 

archtopshop

macrumors regular
Dec 13, 2011
206
1
Well, at 1.5v (the default) all I get is a black screen with the CPUs set on 2.0Ghz. So, adjusting the voltage to 1.65v let it boot, even though I have the issues.

I've already added back the original fan that was not there when I got this machine because it was unnecessary in the previous upgrade. And the processors themselves came with two small fans on the heat sink. I suppose I could try an additional fan and see what happens, but I'm not sure if heat is the issue, versus just the processors. Something to try though. Thanks!
Yep, good luck!
 

gavinstubbs09

macrumors 65816
Feb 17, 2013
1,386
247
NorCal boonies ~~~by Reno sorta
Mods: Not mine! Just helping others out who may be looking for the CPU used in this guide!

Bummer deal that I don't have a bit to spend on a CPU upgrade! I found two things someone might be interested in as I was taking a look through the CPU section of eBay.

Xserve 1.33DP processor card: $79+10 S/H
http://www.ebay.com/itm/NEW-Apple-PowerMac-G4-Xserve-1-33-GHz-Dual-CPU-661-2834-820-1470-A-/350733177070?pt=CPUs&hash=item51a95390ee

Dual 1.42GHz card + copper heatsink: $99.99+calculated shipping
http://www.ebay.com/itm/G4-Powermac-G4-CPU-Dual-1-42-GHZ-Heatsink-/141196509442?pt=CPUs&hash=item20dff7c102

Maybe someone might find a use!
 
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eyoungren

macrumors Core
Aug 31, 2011
21,264
13,115
ten-zero-eleven-zero-zero by zero-two
Bummer deal that I don't have a bit to spend on a CPU upgrade! I found two things someone might be interested in as I was taking a look through the CPU section of eBay.

Xserve 1.33DP processor card: $79+10 S/H
http://www.ebay.com/itm/NEW-Apple-PowerMac-G4-Xserve-1-33-GHz-Dual-CPU-661-2834-820-1470-A-/350733177070?pt=CPUs&hash=item51a95390ee

Dual 1.42GHz card + copper heatsink: $99.99+calculated shipping
http://www.ebay.com/itm/G4-Powermac-G4-CPU-Dual-1-42-GHZ-Heatsink-/141196509442?pt=CPUs&hash=item20dff7c102

Maybe someone might find a use!
Just some friendly advice. You might want to make a note to the mods in your post that those are NOT your auctions and you aren't selling anything.

I did the same as you a while back, hoping to let others know about a good deal I saw and the mods came down on me because they thought it was my auction.

Just saying. ;)
 

gavinstubbs09

macrumors 65816
Feb 17, 2013
1,386
247
NorCal boonies ~~~by Reno sorta
Just some friendly advice. You might want to make a note to the mods in your post that those are NOT your auctions and you aren't selling anything.

I did the same as you a while back, hoping to let others know about a good deal I saw and the mods came down on me because they thought it was my auction.

Just saying. ;)
Dang mods!

All updated. Maybe someone will have fun updating their MDD!
 

harrymatic

macrumors 6502
Original poster
Dec 30, 2013
331
20
United Kingdom
For what it's worth, I've found that the best results for MDD CPU modules are found by putting in the Apple part number - 820-1470-A . Just looking now on eBay US I can see several dual 1.33s and 1.42s - most are around $50. There's even a whole logic board with 1.42 and copper heatsink for $80.
 

desantii

macrumors 6502
Sep 9, 2006
292
19
Aurora, IL
I actually took my dual 1.25 to a dual 1.33 about 10 days ago. Not much of a speed increase...but who cares

Now its running fine at dual 1.33s
 

gavinstubbs09

macrumors 65816
Feb 17, 2013
1,386
247
NorCal boonies ~~~by Reno sorta
So as you guys know my new MDD was running at 800MHz (and I thought the entire time it had a QS CPU, how crazy am I lol). After some research tonight I found out that it was the 133MHz FSB on the single 1GHz MDDs that was locking it down to that speed. I removed the resistor with a flathead screwdriver and took about 15 minutes to remove and re-install the logic board.

Now my MDD is running at a happy dual 1GHz and a 167MHz FSB :)