can you guess the value of this capacitor? - Page 1
Forum section: electronics / repair

author: edb1984
author_rank: Contributor
timestamp: April 30, 2020, 11:46:36 am
content: so I have a graphics card for a PC, its not been switched on in almost 5 years and on the first attempt this capacitor in the photo below blew up.I am thinking i might just bodge on a new one, it's an old card now so it's not exactly going to be a waste if it does not work but it's worth a try.what do you think the value may have been?

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 30, 2020, 11:55:35 am
content: 10μF

author: Manul
author_rank: Super Contributor
timestamp: April 30, 2020, 11:57:31 am
content: Thats on a 12V rail, so you need voltage rating 16V or 25V. 4.7uF - 10uF should be good.

author: mikerj
author_rank: Super Contributor
timestamp: April 30, 2020, 12:08:35 pm
content: It's probably a tantalum, ceramics don't tend to fail like that. It's decoupling the +12v rail so probably around 1uF-10uF and it would need to be at least 16v (preferably higher) rated voltage. The exact value is not critical, and the card may even work without this part. If you replace it with a tantalum cap, make sure you get the polarity correct.

author: Manul
author_rank: Super Contributor
timestamp: April 30, 2020, 12:28:42 pm
content: Quote from: mikerj on April 30, 2020, 12:08:35 pmIt is ceramic (MLCC), they fail like that when isolation fails. It is often that isolation cracks because of mechanical stress. This being near a socket definetly received some flex. Tantalum here is a bad idea.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 30, 2020, 12:53:37 pm
content: As there are several different caps in parallel the value is not very important. This is done to have a wider frequency decoupling function. Dave made a video about this topic. With a bit of luck it can even work with the cap removed. But I actually wonder why that happened. Yes it could be bending stress. I rather think the damage is caused by over-voltage.After fixing the GPU: You should probably check the HDDs/SSDs with a different PC. If they're working and do a backup if not already done. For further tests run the system without the drives connected. If you see the BIOS screen than everything is fine.

author: exe
author_rank: Unknown
timestamp: April 30, 2020, 12:59:12 pm
content: If it's tantalum, then a significant voltage derating is needed, I saw a recommendation to use it no more of 40% its rated voltage. I would avoid tantalums, but that's me. Got one exploded into my face.What's on the other side of the board? Asking because for me it's quite unusual to see three caps in parallel. It's either a mistake, or someone knows how to do it in such a way they don't mutually resonate (few people actually have this skill, so...). If there is no IC on the other side, then it doesn't make sense to have three caps.If so, this cap is a "bulk capacitance" cap and a cheap electrolyte would do it too. May be even better if it has higher capacity. It may also work without it

author: Yansi
author_rank: Super Contributor
timestamp: April 30, 2020, 01:04:36 pm
content: Quote from: mikerj on April 30, 2020, 12:08:35 pmIt definitely is a ceramic.Quote from: exe on April 30, 2020, 12:59:12 pmI have tried to blow up a modern tantalum cap. I had to really try quite hard to get at least a spark from it.Well, I bet they teach that in schools nowadays, even recommend in datasheets. Just put 10uF + 100nF + 4n7 + 100pF all in parallel. Just don't say you haven't seen datasheet with this stuff.

author: edb1984
author_rank: Contributor
timestamp: April 30, 2020, 01:30:29 pm
content: Thanks everyone!!! - I just soldered in a 4.7 50v (it's what I had to hand) and it's working again!Excellent thanks to all 👍

author: exe
author_rank: Unknown
timestamp: April 30, 2020, 01:33:31 pm
content: Quote from: Yansi on April 30, 2020, 01:04:36 pmYeah, modern should do better. There are better types nowadays available, like niobium (https://www.avx.com/products/niobium/). I'm no cap expert, and leave it to the curious reader to do research on tantalum caps safety.As of what happened to me a couple of years go, I wanted to figure out tant cap safety and reliability. I didn't find much info, so I decided to conduct my own research. I bought cheap tans from China, reverse biased it, nothing was happening for the first few seconds, so I thought that they are safe. Next moment it exploded when I didn't expect it. So, at the very least, I wouldn't buy a tant from an unkown source (or, actually, any cap).