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Old 18th January, 2003, 04:08 PM
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8RDA+ vcore fluctuations - how to reduce it

All boards are not created equal - a fundamental rule to our hobby . However, reading various forums it looks like the 8RDA+ has extreme stability problems when using over 2v give or take. Some cant use over 1.9v, others are fine up to 2.1v.

The stability problems are at least partially due to voltage fluctuations which increase with vcore. Here are my readings below, all taken under 100% load (prime95) :

1.5v = 1.49 - 1.51v
1.6v = 1.58 - 1.61v
1.7v = 1.67 - 1.72v
1.8v = 1.74 - 1.83v
1.9v = 1.81v - 1.94v
2.0v = 1.89v - 2.07v
2.1v = 1.98v - 2.21v
2.2v = 1.96v - 2.31v

Now these spikes and dips in voltage increase in regularity as you move up. For example at 1.7v it would be at 1.71v for most of the time, and every 5 minutes or so would dip low then spike high and return to normal again. At 2v and higher the voltage was constantly changing as fast as MBM could report it (on a 1 second dashboard refresh rate).

After messing about with these readings I made my first mistake. I touched the voltage controller after 29 minutes running at 2.2v. I now have a blister the size of my whole fingertip. It gets SCORCHING hot.

So on went a piece of a P4 heatsink. I used a P4 heatsink due to the height. You always want as much surface area as possible with your heatsinks, and when youre looking at such a small base area for the heatsink you need very high fins to make up for it. It still gets very warm running at 2.2v, but its much better.

Results below :

1.5v = 1.49 - 1.51v
1.6v = 1.59 - 1.61v
1.7v = 1.69 - 1.71v
1.8v = 1.78 - 1.81v
1.9v = 1.88v - 1.93v
2.0v = 1.94v - 2.03v
2.1v = 2.02v - 2.18v
2.2v = 2.10v - 2.29v

Much better. Still not perfect though. Next thing is to check mosfet temps. Ouch number 2, and an even bigger plaster. Anyway, out comes the hacksaw and the remains of the P4 retail cooler. 20 minutes later after the arctic epoxy has gone off and were ready to rock and roll again.

1.5v = 1.49 - 1.51v
1.6v = 1.59 - 1.61v
1.7v = 1.69 - 1.71v
1.8v = 1.79 - 1.81v
1.9v = 1.89 - 1.91v
2.0v = 1.97 - 2.02v
2.1v = 2.07v - 2.14v
2.2v = 2.15v - 2.25v

MUCH better. Its still not perfect, but at such high load it never will be. However, when running the chip maxed out its now possible to use 2.2v without random lockups. Some cpu figures below to compare. 1st is before any mods, second after the vreg heatsink and 3rd after mosfet and vreg heatsinking.

2024mhz @ 1.925v. Any more voltage and cpu speed had to be dropped to prevent desktop freezes under load. 2.1v wouldnt even boot windows properly.
2096mhz @ 2.05v. As above again, more volts meant dropping cpu speed. 2.2v would load windows and remain stable, but only at 1984mhz or lower.
2183mhz @ 2.2v. Wheeeeeeeeeeeeeeeeeeeeeee!

Its also improved stability at any given cpu mhz as can be illustrated by the results below :

1900mhz @ 1.75v with no mods.
1900mhz @ 1.725v with the vreg cooled.
1900mhz @ 1.675v with vreg and mosfets cooled.

Your mileage will probably vary depending on how bad your board was in the first place and how much your cpu likes voltage, but cooler chips are always happier chips. Highly recommended as mod - took me about an hour in total to do the mods (not including readings - that took about 6 hours ) and all it cost me was a bit of AS epoxy and a spare P4 retail heatsink off my 1.6a which had been sat in the box since i bought it 12 months ago. A pretty profitable evenings work all in all .

Im playing about with cooling the clock gens at the moment. The FSB clock gen gets VERY hot at over 170mhz (its right next to the AGP slot incase youre wondering). Sticking whats left of the massacred P4 heatsink on it seems to have gained me another couple of mhz FSB stable. Wont put my foot down and say a compulsive yes yet as ive not had chance to properly test yet.

In combination with the VDD mod (540ohm fixed resistor giving me 1.88 - 1.89vdd) im now able to run dual channel mode at 221mhz and single channel at 228mhz. Next up is the vmem mod.

PiLsY.
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Old 19th January, 2003, 03:16 AM
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Good Work Pilsy..... appreciate the effort, even though I had already done mine. Maybe some folks will see this and do the same..... maybe they'll even be generous enough to say TY......

I'll say Thx. for your effort anyway.
( Thx for your effort anyway... heheh)

muzz
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Old 19th January, 2003, 03:33 AM
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Front page stuff Pilsy!

http://www.aoaforums.com/
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Old 19th January, 2003, 04:16 AM
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What again ?

Gonna have to start a statutory charge per post at this rate .

PiLsY.
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Old 19th January, 2003, 04:39 AM
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No, I think AOA can continue to allow you free postage":O}
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Old 19th January, 2003, 05:19 AM
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lol
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Old 19th January, 2003, 05:52 AM
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thats really interesting, didnt know it had that much of an effect, umm 2 questions though, where are the vreg chip an the clock gen. at, a pic would be helpful. maybe ill have to throw some ram sinks on there. good post pilsy
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Old 19th January, 2003, 11:42 AM
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Quote:
Originally posted by Coheed
thats really interesting, didnt know it had that much of an effect, umm 2 questions though, where are the vreg chip an the clock gen. at, a pic would be helpful. maybe ill have to throw some ram sinks on there. good post pilsy
yeah! nice write up ,very interesting stuff ,only could you poss throw some picies of where these things are?
even if you can,t great info :beer:

 
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Old 19th January, 2003, 01:29 PM
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Pilsy, are these measurments taken using UDSM/MM5 or a multimeter.

I think you will probably find that if you use and accurate multimeter the Changes in Vcore you are noticing in the onboard measurment will dissapear.
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Old 19th January, 2003, 02:15 PM
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So basically the boards voltage regulation is perfect and mbm5/USDM make up the voltage spikes and dips yes? And putting heatsinks on the vreg and mosfets fixes this bug in mbm5/USDM? And its this bug in mbm5/USDM that causes people to get lockups or spontaneous reboots when they use over 1.9 - 2.1v (depending on their particular board)? Well I should probably pass on that info to the author of mbm5. Maybe he'll include some heatsinks with the mbm5 download in future?

You get funnier each day Holst :-D.

PiLsY.
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Old 19th January, 2003, 02:18 PM
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My cameras out on loan at the moment, but heres a borrowed image that shows the 7 mosfets (dont forget the small one behind the ps2 ports ) and the vreg. Cheers to OCNZ for this one .

PiLsY.
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8RDA+ vcore fluctuations - how to reduce it-3phase.jpg  
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Old 19th January, 2003, 03:22 PM
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Hmm, them MOSFETs look different to mine, mine are square whereas them have little inward bumps.
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Old 19th January, 2003, 04:51 PM
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Mine are square also and I only have 4. But feel them. Mighty toasty, could stand some cooling. Almost a year ago I bought some heatsinks to cool these but just never got around to putting them on.

I had read else where that this was a way to get a higher more stable overclock. But I didn't know it was because of reduced voltage variations.

Good find PiLsY
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