After several months working with my overclocked Phenom II, I happened to notice something intriguing during play sessions of XCOM: Enemy Unknown, while running CPU-Z. The application would show the CPU clock fluctuating between around 3000MHz and 3400MHz and various values in between. However, the changes in clock speed were not being affected by adjustments to the CPU multiplier; I had disabled AMD's Cool 'n' Quiet in the BIOS while overclocking. Instead, the base clock itself was dropping from it's stock 200MHz, occasionally hitting 180MHz, so I began researching possible root causes. This proved to be particularly difficult, as most of my searches produced results relating to AMD's Cool 'n' Quiet or Intel's Enhanced Speed Step (i.e. adjusting the multiplier). However, I did begin to find some interesting discussions around the strain placed on voltage regulation circuitry when over-volting a CPU.
Voltage Regulation Modules
An important part of power delivery to components is voltage regulation, which is achieved through the use of voltage regulation modules (VRMs or VRegs). For CPUs, these are situated on the motherboard and operate on the 12V DC current delivered by a system's power supply unit (PSU), reducing this to the voltage required by the processor. The topic of how VRMs work is an interesting one, but perhaps a little too long to discuss here and I'm not particularly convinced I'll do a great job anyway! If you're interested in some of the specifics, then I highly recommend watching this YouTube video and reading through this forum thread on the Overclock.net site; coincidentally, both were produced by the same individual (sin0822).
While under normal operation, the VRM generates a fair amount of heat, and it's important for this to be dissipated as quickly as possible. When you factor in the over-volting required to hit certain clock speeds, this becomes even more crucial, so many high end motherboards include VRM heat sinks; such as those on the Asus Maximus Formula I bought recently. The VRMs for the motherboard in my primary system (an Asus M4A77TD Pro) doesn't have any cooling, passive or otherwise. You can see for yourself in the below image; the VRMs are highlighted:
Not only do the VRMs on my board not have any cooling, but I believe the problem is exasperated by my after-market cooling solution for a couple of reasons:
- Stock CPU coolers are designed to blow cool air down over the heat sink. This has the added advantage of the air being pushed across nearby components (including VRMs) as well, helping to move hot air away from them. My H80i closed-loop cooler doesn't push any air across the CPU, nor any nearby components.
- The radiator and fans from the H80i
positioned at the rear of my case protrude over the VRMs, which could be causing a dead-zone where very little air is moving and preventing heat dissipation.
Now, further research on the Overclock.net forums revealed an interesting piece of information regarding Asus VRM design; specifically, the fact that they often use a throttling technique to prevent damage to VRMs in the event they should reach dangerous temperatures. This involves dropping both the voltage and clock speed to keep the temperature down. Certain that this was the problem I was experiencing, I started to investigate the possibility of adding after-market cooling to the VRMs on my board.
Parts List - Passive and Active
After reading the VRM guide and database posts on Overclock.net, I opted to not only double up my passive cooling by adding heat sinks to both MOSFETs and chokes, but also a spot cooling fan to circulate fresh air. I bought the following items:
10x Enzotech Passive Mosfet Cooler MOS-C1 - these fit perfectly over the VRM MOSFETs.
10x Enzotech Passive Mosfet Cooler MOS-C10 - these are for the chokes.
Antec Spotcool 100 Blue LED Fan
Installation
Fitting the parts was quite an intrusive operation, because of the problems highlighted with the VRMs being obscured by the H80i's radiator. So, the first step after removing the side of the case was to unscrew the radiator and move it out of the way:
Once I had a good view on the VRMs, I cleaned them to remove any any dust and attached the heat sinks:
Fitting the Antec Spot cool was a bit more difficult; I think I may have gone overboard with the fan diameter. It was difficult to find a location where I could position it to direct airflow over the newly placed heat sinks. Originally, I'd envisioned placing it directly below them in order to move air up across them and into the PSU's intake. However, that wasn't possible, so I ended up placing it in the middle of the case with the fan directing air towards them as best as possible:
After all this work, I was disappointed to find that the base clock fluctuations still occurred while playing XCOM. Unfortunately, I hadn't been able to take a temperature reading prior to this, so I couldn't tell you if the VRMs had actually been overheating! I suspect now that this wasn't the issue, however, now I'm pretty convinced the VRMs should be nice and cool even with my unlocking and overclocking pulling extra juice.
