Replacement of Chemi-Con KZG with Rubycon ZLJ

[blub0815]

Hi,
is the replacement possible? There is a difference of factor 2 between the ESR/Impedance.
The caps are located on a motherboard.

KZG:
https://www.digikey.at/htmldatasheet...zg-series.html

ZLJ:
https://cdn.badcaps-static.com/pdfs/...a472c7fe84.pdf

BR

[RukyCon]

Re: Replacement of Chemi-Con KZG with Rubycon ZLJ

In terms of ripple current, they're pretty close, almost exact, though the impedance is almost double with the Rubycons. They might still be fine, as the impedance is already pretty low, but I would wait for someone more qualified than me to chime in.

Now since the caps are being used on a motherboard, it might be possible/easier to go with 'solid polymer' electrolytic capacitors. Since they're pretty common now and don't cost that much more than standard electrolytic capacitors.

[momaka]

Re: Replacement of Chemi-Con KZG with Rubycon ZLJ

For any of the KZG and KZJ that filter power for the CPU VRM or any other buck regulator output, then you might have to find replacements with ESR closer to KZG and KZJ. ZLJ will likely "work" too, but the ripple & noise may be higher, which may or may not be an issue (particularly with overclocking, higher-power CPUs, or large capacities of RAM.) So it depends on what the KZG and KZJ caps were filtering before. For example, the CPU VRM is buck-regulated, and so should be recapped with caps that have ESR that is closer to the originals. Since high-capacity low ESR "motherboard grade" electrolytic caps are not available for sale anymore anywhere, the common remedy is to go with polymers, as RukyCon suggested. Polymers usually come in smaller capacitance, though. However, it's generally OK to drop the capacitance up to 1/2 of what the electrolytic caps were (i.e. 820-1000 uF polymer in place of 1500 uF electrolytic and 1500-2200 uF polymer in place of 3300 uF electrolytic.) Polymers also tend to be more easily found for lower voltages (such as 2.5V and 4V.) With that said, for any "large" capacity 6.3V KZG and KZJ caps right next to the CPU heatsink - these usually filter the CPU VRM. So if you use polymer replacements for these, you can usually drop the working voltage down to 4V or even 2.5V (exception: if the KZG/KZJ caps had 16V rating, DO NOT drop the voltage rating - keep it at 16V.)

Now, you may not need to replace every KZG/KZJ with polymers. Again, it depends where they are all located and what they filter. Any KZG and KZJ that are near or are electrically connected to an inductor or toroid of some sort - these will likely filter a buck-regulated rail, so you can use the same method as when recapping the CPU with polymers (but usually, it's better not to drop the voltage rating for these, unless you know the voltage of the rail the polymer caps will go on.) Otherwise, for the rest of the board (i.e. caps between PCI / PCI-E / AGP expansion slots, caps near USB headers, and small-medium caps close to I/O port area), ZLJ should be just fine. If available, I think ZLG, ZLH, and ZLS might offer slightly better ESR spec. Panasonic FR, FM, and FS, along with Nichicon HV and HW are good alternatives too, if those can be found easier where you are.

What motherboard do you have, BTW?

[blub0815]

Re: Replacement of Chemi-Con KZG with Rubycon ZLJ

Thanks for the elaborate answer!

The motherboard is a GA-K8NXP-SLI. This is very rare and hence I want to be sure with the replacement caps.