A few questions about the ka790gx and dka790gx

Question

i have a few questions about the ka790gx and dka790gx , how much better is the dka790gx compaired to the ka790gx ? . how much difference does the ACC function make to overclocking etc , i plan on getting a phenom II 940BE or 720BE . i already have the ka790gx so would it be worth building another system using the dka790gx mobo , or should i keep what i already have and just change the cpu ?

Answer 1

It's largely irrelevant what other boards had VRM issues other than the KA790GX - the fact is it died at stock settings. Since there is little cost difference between the more robust DKA790GX (or Platinum if you really need 1394) why bother with the proven weakling? There are other examples around of the KA not having a robust power section.  There's no way I would use even a 95W TDP CPU in the KA and absolutely not O/C.....!
As for the credentials of Custom PC, I have generally found their reviews accurate and balanced, and echo my own findings where applicable. If a little too infrequent.
The fact that the KA has such a huge VRM heatsink leads me to my other comments on the Forum, particularly regarding the "fudge" aspect:
"""Henry is spot on - the notion that adding a heatsink to the top of the D2PAK or whatever MOSFETS is effective is virtually worthless. The device's die thermal junction is the tab on the device back - which is always against the PCB pad. The majority of heat is therefore dissipated in to the board, and the fact that the epoxy plastic encapsulation gets hot is simply due to the inability of the heat to be conducted away from the device die via the tab. Not sure when Epoxy become an effective conductor of heat.... Good practice is to increase the size of the PCB pad (or "land" in American) such that the enlarged PCB copper area acts as an adequate heatsink. This is still not as effective as clamping a power device tab to an actual piece of ali or copper, but since the devices used are SMD devices, this is not possible. However, the surface area required to provide sufficient PCB copper area to act as a heatsink for several devices isn't available in the current motherboard layouts. Where industrial SBC designs differ in this respect is to place the VRM MOSFETs on the back of the PCB on very enlarged PCB pads - where real estate for components is not an issue.
Gigabyte's UD3 2oz copper mainboards sound like a good idea, on the face of it. However, without knowing how they have connected the device tabs to where and what remains a mystery. I suspect it is more hype than solution, although there will be some positive effect. From an electrical perspective, having lower resistance connecting whatever to whatever (probably just a 0V plane) is no bad thing.
The way the likes of ASUS sort of get round the problem is to increase the sheer number of MOSFET devices and effectively spread the heat dissipation over a larger physical area. This works to a degree, there is the same amount of heat being dissipated, but over several more square inches. The other advantage of this is that each leg of the VRM circuit passes less current and therefore localised heat is reduced. Remember that as well as absolute peak operating temperature causing reduced component life, thermal cycling stresses the mechanical aspects of components (die wire bonds for example) as well as the solder joints on the board. Keeping components at a relatively constant temperature, even if this is high (but within operating temperature limits), is a means of promoting longevity.
For myself, the first thing I do with a seperate VRM heatsink is take it off and use a quiet fan to blow air on to the VRM area of the PCB - this is where the heat is. This has the added benefit of actively cooling the inductors and capacitors too....
Cooling the epoxy component body is a fudge. If the epoxy (and thus any heatsink plonked on top of it) is running at 60C, the component die is way above that.....
It's better than nothing, but only just."""