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Old 01-01-2023, 10:24 PM   #1
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Default psu mlcc

i came across dead seasonic prime psu with shorted mlcc caps on the modular board, this is the third time i encounter this problem, i usually just removed the shorted mlcc and not replace them since theres a lot of caps around the psu i used to think those mlcc probably does not matter much, i have no equipment to test or proper knowledge for this. i just reuse those psu on low end machines. but few days ago one of the machines have its 2 sticks of ram died, it keep on getting blue screens. 2 sticks of ram died at the same time, its probably something else and not just the ram. in the past when a board kills ram its usally a sign of a bad filtering cap on the memory vrm, but the board uses solid caps, so im thinking those mlcc that are removed from the psu may have increased ripple? if so what value of caps should i be using to replace those mlcc's? will a 10uf 16v electrolytic be fine?
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Old 01-02-2023, 06:48 AM   #2
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Default Re: psu mlcc

like you said, ram has it's own regulators - so i'm not sure the psu caused it
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Old 01-02-2023, 10:36 AM   #3
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Default Re: psu mlcc

Originally Posted by jescolta View Post
if so what value of caps should i be using to replace those mlcc's? will a 10uf 16v electrolytic be fine?
The MLCC's are there probably for suppressing high-frequency EMI/RFI - something the electrolytic/solid polymer caps may not do, due to much (relatively speaking) higher ESR. So adding small electrolytic capacitors in place of the MLCCs is pointless.

That being said, the removed MLCCs very likely aren't responsible for the RAM dieing. Indeed RAM has its own voltage regulation system (sometimes multiple buck and linear supplies in cascade), so any voltage spikes from the PSU don't have a chance of making it to the RAM at all.

Of course, if you still want to replace the MLCCs for piece of mind, use same or similar values. I'm not 100% sure what values to expect these days given a certain size for an MLCC... and it will also depend a lot on the voltage rating of the MLCC too. But in any case, 16V, 25V, or 35V MLCCs of 1 to 10 uF will probably match very closely to what was in there before (that is, if you have no way of removing any of the remaining MLCCs and measuring them.) If you have any scrap motherboards or video cards, you can pull such MLCCs from near the CPU area - just make sure to use the ones that are connected to the 12V rail for the CPU, as those are probably rated for 16-35V. The ones connected to CPU V_core may only be rated for 6.3V or less and likely will self-destruct if you connect them to the 12V rail.
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Old 01-02-2023, 10:57 AM   #4
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Default Re: psu mlcc

I can't believe a SS Prime would have this problem. They've been nothing but awesome with me
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