Identifying and testing SMD capacitors - Page 1
Forum section: electronics / beginners

author: Johnny5
author_rank: Newbie
timestamp: April 07, 2014, 02:53:54 pm
content: Hi folksMy first post, but have been looking at the forum for weeks and watching Dave's fantastic videos.But thanks to Dave i now have another hobbyI have done a few repairs and made a few kits, but now i have set myself a goal.I have in the garage some old 90's retro intelligent lights which i picked up from a job hoping to repair, sat in the garage for years.My goal is to repair these for our family NYE party and show off my new slowly aquiring skill.So far i have managed to test and replace most of the faulty components.... BUTNow i have the task of checking those damn SMD capacitorsFirstly they have no markings on them what so ever!I did get a schematic for the board , but that only tells me the values, but not the size or type of smdHow do i find out what caps i have and whats the best way to test them?Sorry for the long ramble but i just thought it would be a good way to introduce myselfAll the bestJohnny

author: peter.mitchell
author_rank: Super Contributor
timestamp: April 07, 2014, 03:10:45 pm
content: There are a few types of SMD capacitors, ceramics chip capacitors, tantalum capacitors, electrolytic capacitors and film capacitors.Ceramic capacitors are pretty easy to identify, they look like a brown block with metal ends - they look burnt if they are bad, generally and will pass most tests unless this is the case.Tantalum capacitors vary in looks, but here is what they can usually look like;, they usually look a-OK until they go pop and then they look like this;Electrolytic capacitors look like little cans. The surface mount ones usually don't show any signs when they are bad, although they do get physically hot.Film capacitors are pretty uncommon in surface mount devices, so you can fairly safely ignore them, but for identification purposes, they look something like this;The ceramics/tants/films will all be pretty much perfect until they catastrophically fail, electrolytics slowly go up in ESR, getting hotter and hotter until either they pop or just become completely useless.

author: theatrus
author_rank: Frequent Contributor
timestamp: April 07, 2014, 03:17:15 pm
content: Ceramics and to some extent tantalum and certain polymer caps come in a range of standardized sizes:http://upload.wikimedia.org/wikipedia/commons/thumb/3/34/SMT_sizes,_based_on_original_by_Zureks.svg/330px-SMT_sizes,_based_on_original_by_Zureks.svg.png(Do note that a metric 0402 is nowhere near in size to an imperial 0402 - I have accidentally ordered the "grains of sand" 01005 (metric 0402) parts before)Its common for a board to pick one size and stick with it, unless voltage or capacitance dictates otherwise.

author: Johnny5
author_rank: Newbie
timestamp: April 07, 2014, 03:31:24 pm
content: Thanks Petersorry i should have been a bit more specificI did mean ceramic capacitors .. the ones i have on the board have no markings, i would like to find out how to identify whether they are class 1 or 2 or if they're X7R etc etc and what package sizeI have managed to suss the other types due to Daves great video .. but these damn ceramics are a pain in the ass

author: theatrus
author_rank: Frequent Contributor
timestamp: April 07, 2014, 03:43:49 pm
content: In general, buy the best dielectric you can (NP0 > X7R > Y5V) for the capacitance and voltage needed for the size of the part. Voltage would need to be determined in the circuit, and capacitance of a good cap via an LCR meter. There are no reliable indicators of what properties they have without testing.However, ceramic caps rarely fail - its not something you need to watch for unlike bursting electrolytics.

author: Johnny5
author_rank: Newbie
timestamp: April 07, 2014, 04:19:46 pm
content: Thanks theatrusSome of the ceramic caps are coupled with the electrolytic caps, so i was going to replace them in case i heat damaged them .I am going to replace all the ceramic caps, just basicly down to the age ... they are all Samwha SD and have manged to get the same spec to replace with .would i be safe with X7R caps or would it be best to over spec to something else?Also what brands are the good ones ?With regards to LCR meters, what is a good hobbyist one to go for ?btw that's a great chart, i shall rint that off later and use it for reference in futureThanks for the help, i'm really starting to get into working with boards now, i've always managed to shy away from it until i got hooked on the eevblog videosEven my other half said Dave's slogan " Dont turn it on , take it apart " is me all overMust order a t'shirt haha