8RDA+ high Vcore shutdown fix!

[Spartacus]

The 8RDA+ is a great board, about the best around for AMD overclocking right now. Even so, a lot of dedicated mobo abusers (myself included) have had a problem where the 8RDA+ would just shutdown at Vcore settings over 1.9v even though the board is rated to provide 2.2v Vcore.

The symptoms of this problem are that while running the CPU at 100% load (Prime) the system will totally shutdown. The system will often boot fine to the Windows desktop even with Vcore set at 2.0v. The shutdown can happen instantly upon starting Prime or sometimes not for 30 minutes. Generally, the higher the Vcore is set, the quicker the shutdown. My 8RDA+ would run Prime for quite a while at 1.925v but would shutdown eventually. Setting my Vcore for 2.0v guaranteed a shutdown in 30 seconds or less.

This problem makes it impossible to achieve a decent overclock because the 8RDA+ shuts down much too soon. I spent a lot of time looking at CPU temp problems, even going so far as to disable the AXP's internal diode for temp sensing. High CPU temp causing the shutdowns didn't make sense though because I was able to run the same 2400+ cpu at 57C (!) perfectly stable on my old KR7A. The 8RDA+ was shutting down with CPU temps only around 40C. Next I thought that maybe the 8RDA+ MOSFETS or voltage regulator were overheating. Nope, same symptoms with cold air blasting at the power section on the mobo.

OK, I've covered a lot of possibilities but no payoff yet. I started looking at the IRU3055 Vcore voltage regulator. It's job is to control the switching of the power MOSFETS providing power for the CPU. Looking at the datasheet:

http://www.irf.com/product-info/data...ta/iru3055.pdf

I found that the IRU3055 also has overvoltage and overcurrent protection. Hmmm, that's sounds like something I need to look at. I originally thought that maybe cutting or lifting pins 15 & 19 might keep the overvoltage circuit from shutting down the system. Then I realized that there is no overvoltage condition causing the shutdown. The voltage in the MBM log is always fine at shutdown. Ok, that leaves the overcurrent protection circuit.

Pin 16 of the IRU3055 is called "OCSet". It needs an external resistor to provide the threshold for the overcurrent shutdown. So Epox would need to pick a resistor value to protect the power section of the mobo (and CPU) and make sure that the value they select will allow high enough current for overclocked conditions but still shutdown the system before a meltdown. Could that be where the problem is? YES!

Due to mobo component variables and operating temp variables, the value of the resistor (I didn't measure it) that Epox selected is causing the system to shutdown when it should not. In short, the IRU3055 is being programmed to be over protective.

Here's the fix: Cut the trace leading to pin 16 on the IRU3055.
I used a flashlight, magnifying glass, and an X-ACTO razor knife to cut the trace. In my system, I pulled the power supply aside and could see the IRU3055 very clearly. It took about 30 seconds. Sorry, no pics. I don't have a decent digicam available.

Now the IRU3055 has no idea how much current is flowing through the MOSFETs. It will happily supply current until everything overheats, your system catches on fire, and burns your house down! That's the way every hardened overclocker wants it . YEAH!

Now I don't really think that will happen, but if it does, I will laugh at you and call you names! If you choose to do this mod, it is ALL AT YOUR RISK! This mod will also void your warranty (duh). The "right" way to do this mod would be to replace the resistor with a value that will allow more CPU power, but still provide some protection. Just cutting the trace completely disables overcurrent protection. You have been warned! The circuit is not a feedback/correction loop though, only a protection circuit.

Good luck guys!

NOTE: If you don't feel comfortable doing board mods and cutting traces, PLEASE don't do this mod yourself. Get help!

DDTUNG: Thanks for posting so many of your mods, I posted this mod here first.