An upgraded power module (VRM) for the Power Mac G4 CubeDesigned by Cuebus Upgrades in United States of America
The G4 Cube SuperVRM is an upgraded power module (known as the VRM) to support CPU and GPU upgrades that take more power than the originals. Most Cube owners are aware of the fact that the stock VRM …Read More…
The G4 Cube SuperVRM is an upgraded power module (known as the VRM) to support CPU and GPU upgrades that take more power than the originals. Most Cube owners are aware of the fact that the stock VRM is overloaded when supplying the power needed for any upgrades and the risk of failure means potentially frying your motherboard and its components.
Enter the SuperVRM, which takes the original VRM design and upgrades the specific components that are likely to fail. The original design by Apple (largely following a circuit released by Linear Technology in an application note) used a cutting edge voltage controller at the time, the LTC1628, for the 5V and 3V3 rails. Since the voltage controller itself has never been an issue in the original VRM, I decided to go with the same proven circuit, but upgrading to 5 MOSFETs per voltage rail from the original 3, each with a power pad that is soldered to internal copper planes. Heat dissipation is extremely uniform and even across the entire module, meaning there are no individually overheating components. With the addition of slightly larger inductors and more bulk capacitance, power also stays in regulation over larger loads as well as fast step-loads. Apple used the LM2678 by National Semiconductor for the 12V rail, which supplies up to 5A, more than enough for all the 12V needs the Cube will ever have. Therefore, I've left this part of the circuit mostly the same, with a few small changes such as polymer capacitors instead of electrolytic and larger polyfuses to allow the maximum current draw.
This module is designed to be a drop-in upgrade with all connectors in the same place, and an identical PCB (no removal of one of the pillars needed!)
This VRM has been tested on two Cube machines, both with upgraded CPUs and GPUs. An important note: I do not recommend installing this VRM in stock form for dual-CPU upgrades, especially dual 1.7ghz and above, due to the fact that the motherboard of the cube is not designed to distribute that much power. The connector itself is rated only up to 15A on the 5V rail (21A on 3V3), and with a dual CPU you are drawing close to 100W. There is a reason that these CPUs generally came with a VRM bypass solution- putting that much power through any VRM in the cramped space where the VRM sits is asking for trouble. If you need a VRM relocation harness, please check my other listing here here.
Assembly is done entirely by me on my home production line, using lead-free solder and a reflow profile optimized for this dense circuit board on an IR reflow oven. It is RoHS compliant. PCB is 4 layer, 155Tg FR4.
90 day warranty on the VRM module only. If there is enough interest, I may be able to retroactively extend that to 6 months or a year in the future.
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