ASUS P5K Capacitor Mod

Why Mod?

The motivation is to prepare this board for a quad-core CPU. There have been reports of caps blowing up with the P5K series of boards when pushing a quad-core CPU to the max. In most cases the caps that blow up are either on the CPU VRM side or on the source ATX 12V connector side.

There can be two possible reasons booth which have a cascading effect.

1. Since the P5K sports only a 3-Phase VRM, the ripple current is going to be larger. This means when large currents are drawn by a highly OC'ed quad-core, the ripple current will increase as well. The problem here is not just the current draw, but the slew rate, i.e the time-rate of change of current. When the Slew-rate beginss to increase as the draw increases, so will the ripple current. At some point this will exceed the ripple current rating of the capacitor leading to a kaboom!
2. Another way of looking at this would be to understand how a multi-phase VRM topology works. In an n-phase power distribution scheme, power is divided into n-phases that are offset by a fixed angle. To understand this, we have to consider only the AC part of the current from the voltage regulators (i.e ripple current). The purpose of the n-phase offset is to ensure that the average AC current is close to zero due to destructive intereference between the AC components. These phases are controlled by the PLL IC and the duty-cycle regulator ensures that the desired current amplitude is maintained. When highly overclocked, there can be a phase mismatch because everything is operating far out of spec, so this in effect contributes to a large ripple current.
3. As the current draw from the PSU increases, the teeny 16V 270uF Solid Cap turns out to be insufficient. You can see on the silkscreen that there is space for more. If the ripple current rating of the ATX12V cap is exceeded it blows as well.
4. Having no filter caps near the 24 Pin connector also worries me a bit. I'm going to use a 16V 1500uF Chemicon LXZ in that location.

What to mod?

1. Add 16V 1500uF or 16V 680uF Chemicon LXY near the ATX 12V connector.
2. Add 4V OSCON SEPC near the phase inductors.
3. Add 6.3V 680 uF Nichion Conductive Polymer near the FETs.
4. Add 6.3V 680uF Nichion conductive Polymers near the chipset.

Pictures:

What a good mod for the P5K. There are storeies on the web of these caps bursting.

The higher end board like the P5K Premium should not need this mod right? The area around my socket is loaded with caps and mosfets, cooling etc.

Ranger, sometimes Premium's have had caps blow up on them as well. But that would be the ones near the 4 pin ATX connector and not on the CPU VRM side. I should be getting a board sometime this week to work on. I'll keep you guys posted.

Good work SN, a cap-mapped before/after shot would be good so people know where your actually placing the new caps...I can only see three in the pics

Super Nade said:

Ranger, sometimes Premium's have had caps blow up on them as well. But that would be the ones near the 4 pin ATX connector and not on the CPU VRM side. I should be getting a board sometime this week to work on. I'll keep you guys posted.

Click to expand...

The Premium\Black Pearl has an 8-pin 12v ATX..You're talking about the connector by the CPU right?

No hiccups. Installed the board today and ran memtest for a few hours. I'll be doing a bit of OC testing tomorrow.

I hate these ROHS multi-layer boards. Cleaning out the holes is a major PITA.

Use a mini drill.

A drill would rip through the contact pads and adjoining thermal pads. I won't recommend it for a multi-layer PCB. OC did not increase by 1MHz, but that was expected. My CPU has hit a wall. However, I expect more stability during sudden load changes. If I had the time, I would have replaced all the Fujitsu's with the SEPC as well.

I drill them all the time, the drill is the slightly over the size of the cap leg.

Wow good stuff. Makes me want to pull my board and check for bulging caps, but the Premium Black Pearl has a much beefier power circuitry....

You won't see any bulging caps. The stock ones are pretty good (Fujitsu). It is just that all locations are not populated. Usually, I'd like to fill up the CPU VRM and DRAM sides.

Hmmm... I just got a new p5k. It's the same revision as yours but mine has blue caps, instead of red. Are they the same inside?

Blue = United Chemicon. Red = Fujitsu FP-Cap. The blue ones are good too. You should have no problems. They are the same.

Hello, sorry to bring an old thread back from the dead.

I would like to improve my P5k as you describe, but I cannot see any of the pictures, if there were some shown that is.
Just installed a q6600 and it does get very hot around that area. I pencil modded the vdroop.
After reading about the 3 phase not being great, I have left trying to run the CPU at 3.6ghz and above until I can try to improve the power to the chip as you describe. I placed some DIY HS's on the MOSFETs at the top of the board above the CPU, as I noticed it was getting to 135c+ when Priming for stability at 3.6ghz.

I have searched about, Super Nade seems to be the only person that has described this mod. Can find no other talk of it elsewhere.

If anyone could post some pictures or pointers as to how to go about it, it would be fantastic.
I have a soldering iron and a steady hand, and have done a few basic mods before. I could only copy from a diagram though as the electronics talk is a bit beyond my knowledge.
I hope to buy the parts at Maplins maybe, or take off an old motherboard.

Thank you for your time.

Edit:
After lots of probs, I reinstalled Firefox, and can now see the pictures, which makes this whole post completely pointless

No worries, if there is anything I can do to help let me know.

Welcome to the forums!

Since we like new members, if you send me a self addressed envelope with postage I'll give you the OSCON-SEPC caps for free (I do have some left over).

Much appreciate it.
I would love to send a stamp addressed, envelope, but I'm over the pond in the England.
I will get some photos of my P5K and post them here, so you could show me where aboutsexactly to place the new components, if that's ok by you.
I have only ever really done basic voltage mods on graphics cards. And soldered a few broken chips back onto boards for friends. So want to get it right, so I don't blow up my motherboard
I was looking at the local electrical component store, but could not find the parts you listed. (only due to my lack of knowledge), as I'm sure they must have them. I just not so sure what I was looking for.
I was going to try to get them from here:
http://www.maplin.co.uk/Sub_Category.aspx?Menu=-2
This store is in town, and have bought other bits n bobs from them in the past. Only resistors though, components wise.

I will borrow a camera and take some (hopefully clear) pictures to get the ball rolling.
Thanks again!

Edit: Just noticed in your thread about suppliers. Digi-Key seem to have a UK branch too. http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=131081;keywords=capacitor My failure to find the parts continues though. I am really pretty dim looking at the filter list on these sites.

Perk, after extensive searching on that site, I would not recommend any of those caps they have there. Seems pretty generic to me.

On the digikey site:

565-3038-ND
565-3233-ND
565-3255-ND
565-3228-ND

These should meet all your needs. I would go with 680uF or 820uF on the CPU VRM side, 560uF on the DRAM and chipset side, while going with the 330uF 16V caps on the power supply locations.

Great!
I will be borrowing a camera some time over the weekend, and will get some screens up. Then can work out how many of each needed to do the job.
Will post back soon as I've done that.

This post is intense, thats some crazy stuff there SN. Well done though.