Memory capacitor polarity

[craig588]

I have a stick of BH5 that clocks bad....very bad. It tops out at 198MHz on a good day. It was given to me because the previous owner somehow managed to knock off a bunch of the caps in the top row. They said it used to do 225MHz for them no problem with 3.1V. I plan to replace the top row of caps with some electrolytic caps, but I need to know the polarity.

I have a lot of disc caps which I belive are non polar, if I can't find out the polarity of the caps could I just use a few of these or would they have too high of input resistance?

[Tatewaki]

most cremaic caps (brown color) are not polarized

[craig588]

yes, that is why I can't use one of my other BH5 sticks as a reference. I really want to use electrolytic here. Hipro5 did it, but in his pics the polarities are obscured because he was acctually taking a picture of the memory label and not the mods.

[Holst]

Caps will usually run from V+ to ground.

You should be able to look up ground pins on the memory DDR DIMM spec sheets (should be on the JDEC spec) then you can use a multimeter on continuity to work out which side of the cap solder point is ground, the other should be V+

[Holst]

You should be able to use some decent electrolitics just fine, you may want to experiment with values as ive never tried this myself.

[STEvil]

SMD ceramic capacitors are usually for signal quality reasons and to keep voltage jitter down.

[craig588]

I couldn't get the system to boot with the electroltic caps, so I just went with disc ones and it's working fine. It's acctually clocking past it's old limits. Too bad I don't have any working benching systems right now, it seems like it would be a fun stick to play with. My current benching mobo doesn't like using the 2nd side of any stick at any speeds past 240MHz, but it was playing with the 1st side of this stick error free in memtest at 280MHz.

[reject]

so memtest shows errors only in the xxx-xxxmb region and not the first half?
wat mobo

[craig588]

The DFI NF3 LP UT.

I belive part of the problem is I trashed it with LN2. Something got too cold on it.

[kryptobs2000]

hmm.. would it be possible to do a cap mod to any normal stick and would it increase ur oc? Got any pics of urs or something, I might try it if this would work.

[enzoR]

i did a pacs mod to my ram this morning. soldered 1000uf electrolytic low ESR from a dead mobo in parralell to my rams smoothing capacitors. voltages remain really stable now going from load-idle. it gained me 3mhz. i think i should do it to the VTT aswell.

[craig588]

Just take any ceramic disc caps with a voltage rating higher than the maximum you plan to take your 3.3 rail to, the higher the farad rating the better, and solder them to both sides of the little ceramic caps on the PCB. I love this mod, I did it to a few other systems and it helped with cold boot issues that one of my mobos had. It also raised the clocks I was able to get out of some generic 2100 ram on a old pali system.

Why isn't this mod done more often, or talked about more freqently? It is incredible!

[celemine1Gig]

Could you please take some pics. Pics often tell more than thousand words.
This sounds to be a mod for me.

[craig588]

I don't have a camera, when I take photos I always need to borrow a friends. I'll have some sometime this week though.



Oh, just so people know, I wasn't doing 280MHz with 3.1V, it was with 3.7V.

[celemine1Gig]

What about some pics? Did you already have the time and the opportunity of taking some pics?

Would be really nice.

[stealth17]

bump

[craig588]

I still have the stick, it's dead now though. This isn't the safest mod either because it greatly increases the startup current required and I have killed one mobo because of it.

It's a fun thing to try though, everyone should experiance it.

[stealth17]

I just put 4x100uf 16v on and I either got worse results or it didnt help at all. It was kinda hard to tell because the BH-5 was heating up a lot and with the caps on there I couldnt run 2x80mm fans directly above it.

[celemine1Gig]

If you try this mod you should use eiterh SMD ceramic caps, or radial 6.3V 105°C extra low ESR caps. Using caps with a high ESR could be the source for the problems here.

[SoddemFX]

The 100uF is way overkill, 10 or 47uF low ESR are much more suited or as celemine1Gig has said some ceramics, or both...

ESR shouldn't decrease performance, this just limits the amount of current which can be transfered by the capacitor. It might make the modification ineffective, but the ESR of the new capacitors on its own shouldnt decrease performance or cause any harm.

Maybe this large bulk capacitence wasn't needed anyway and the increased inductance from the capacitor leads has just made the existing capacitors on the DIMM and board now not only supply current to the IC's but also compensate for the series inductor?

I think that additional bulk capacitors to reduce ripple such as low ESR electrolytics should be added to the motherboard with only small value -probably ceramics, being soldered directly to the DIMM PCB. Just my opinion

Tom

[stealth17]

are all ceramics the same? like are there ESR and low ESR versions?

[SoddemFX]

Alu. electrolytic << tantalum < ceramic

The ESR in a ceramic is very very low, 1 to 5 milli Ohms typically. You can ignore it.

For removing ac ripple you can use electrolytic with low ESR, for high frequency noise you must use a ceramic because the ESL dominates in the high frequencies and alu. electrolytic even when mounted with very short leads have very high ESL.

I drew this in Word, it was a few years since i last studied this so it might be a little off but this shows how ESR and ESL act on a capacitor. The scales are both log. The green line shows the ideal capacitor which blocks DC and passes AC.

Hope this is of help

Tom

[stealth17]

so what value and voltage ceramic should I get?

[SoddemFX]

I'd put multiple 100nF ceramics on the DIMM PCB (maybe one per IC) then some 47-100uF low ESR electrolytics on the back of the motherboard DIMM socket bettween supply voltage and ground...

Tom

[Hound]

just curious, is there anywhere where i can learn more about this, i plan on going to uni anyway, but since i gotta finish school first (damn waste of time that is) how would i learn about electronics? and to make this (barely) on topic, where do i start with ESR & ESL?