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cooling? Yikes! | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| DISCLAIMER/WARNING:
First and foremost I want to stress that modifying to cooling, clock speed or CPU voltage of PowerMacs will void your Apple warranty. Once the label over the jumper
block is removed, no Apple Authorized Service provider will perform warranty
work on that system regardless if the problem is motherboard or CPU related!
Adding a Peltier cooler involves mods that may destroy your mac or result in
personal injury if improperly done. Do not try this at home. The following information is for reference/entertainment only, and is not recommended to others by xlr8yourmac or the author. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Introduction: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
For some introductory information as well as the jumper block settings required
for this modification, please refer to my first article, G4
Overclock. This article doesn't pertain to any of the new AGP G4s, although
some information may be usefull. This article will mostly benefit B&W G3
and Yikes G4 owners. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The Voltage Boost: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Previously, my stock G4/400 Yikes! would not boot at 500MHz. It would simply drop into open firmware. So my first decision was to boost the core CPU voltage to achieve 500MHz. Before I did this, I removed the jumper block and soldered a 10 way dip switch to the jumper block pins. This way I can switch CPU and bus speeds in a matter of a few seconds. Without this modification testing would have been a complete headache. A wire wrap tool works great too. Just put your jumper block in a safe place, and forget messing with jumpers ever again. Boosting the core voltage allows for cleaner signals within the CPU, but increases power consumption and therefore heat. This modification can be tricky, and two fine tip irons are highly recommended. I also had the aid of a microscope built for soldering and PC board work. The controlling resistors are at positions 43, 25, 26, 27, and 28. These control VID codes 4,3,2,1, and 0, respectively. A zero denotes a 100 Ohm resistor and a one is an empty spot. Your model may have a different resistor value, 101 is 100 Ohms, 102 is 1000 Ohms. The Yikes comes stock at 2.1 Vdd, or a VID of 11110. The easiest jump is to 2.4 V. This can be done by moving the surface mount resistor from position 43 to position 26, for a VID of 11011. This is still below the max rated voltage of 2.5 V +or - 0.1 V.
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| The Peltier Junction: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
I was ecstatic to see my G4 boot at 500Mhz. However, it crashed after about thirty minutes of heavy mp3 and mpeg movie playing. Temperatures were in the 130s. I lowered the backside cache speed to see if the cache was the limiting factor. The machine still crashed with a 200MHz cache. Clearly is was a temperature problem, because the system runs stable at 450/225. So I ordered a 30mm x 30mm thermoelectric cooler from AllElectronics, part #PJT-1. I found a piece of aluminum about 1.25" square and 1/8" thick at work. This provides even cooling from the peltier to the surface of the CPU die. I also purchased three 10 Watt 10 Ohm power resistors from a local electronics store. They were wired in parallel to achieve a total resistance of 3.33 ohms. The resistance of the peltier unit was measured to be approximently 8 ohms. So with roughly 12 ohms of load and a 12 Volt power supply, the peltier will drain 12 Watts maximum (P=V^2/R). Just remember yellow to black on a power connector will produce 12 Volts potential difference. Red to black is 5 Volts. I found 5 volts to be insufficient. The Apple OEM heatsink was placed on the hot side of the peltier. With this setup, I did not have to shave down the heatsink, everything fit great. I used wire with the stock heat sink clip to attach the heatsink/peltier to the socket. The resistors are laying in the zip bay. A future improvement could involve moving the resistors outside of the case, to keep the ambient case temperature lower. The resistors generate quit a bit of heat, and are too hot to hold for more than five seconds. I installed a 35CFM 80mm fan hanging from the zip bay. Rubber bands are holding it directly over the heatsink, so the CPU receives plenty of airflow. With the current setup it boots into openfirmware at 550Mhz, and is unstable at 520 MHz. I believe anything over 500MHz will be unattainable due to the errata bug in stepping 2.6 G4s. I did not include temperatures because I believe those readings are not very accurate. My system runs in the 100-120 F range regardless of speed and cooling, from my stock G4/400 to the G4/500 with peltier and fans. Also, there is no condensation at all, but I leave my computer on 24/7. Below are my results from many hours of tinkering.
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| Synthetic Benchmark: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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For all benchmarks, best score/times are highlighted yellow.
Macbench 5.0, OS9, extensions off.
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| Real World Performance: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Adobe Photoshop 5.5 w/AltiVec Plug-ins 12.3 mb 300dpi 24-bit RGB scan 125mb allocated OS9 Glass Distort: 20 Distortion, 15 smooth, Frosted, 100% Radial Blur: Amount 10, Spin, Best All times are in seconds.
distributed.net RC5 client v2.8007.458 AltiVec enhanced for cracking RC5 keys. All numbers are in keys/sec.
* Same as others but booted with extensions disabled. ** Crashed immediatly after finishing benchmark. Can you say stepping 2.6 erratta?
G4TimeDemo Altivec Enhanced 3d game engine by Altor Systems Amazing detail, thousands of colors. Rage 128 OEM
I'm not sure how accurate this benchmark is.
Unreal Tournament 4.05b3 Highest quality graphics, low quality sound. 800x600 Rage128 OEM OS 9 OpenGL 1.1.2 130mb Allocated. [FPS may vary a fraction of a FPS in normal run/run variation.]
OS9 with OpenGL 1.1.3 and ATI Drivers from 9.0.2.
Looks like the Rage128 is the bottleneck.
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