Trying to identify smd caps/resistors - Page 1
Forum section: electronics / projects

author: shant
author_rank: Newbie
timestamp: August 09, 2013, 01:35:15 am
content: Hello guys, i just registered and i have very basic education in electronics so far and willing to learnanyway i have a computer motherboard here that has 5 smd components broken off in series,those are connected to the sound chip, although the sound itself is working (if im not mistaken there is a buzz in the sound),id like to repair it anyway,im not sure if they are capacitors or resistors and i also can't find out their values because its not stated on the pcb, i tried measuring the ones next to it (they look the same) but some people told me that i would get wrong value if i measure on the pcb itself, not sure how true that is, what is the easiest way to find out the value ? here is a picture of it, thanks a lot!

author: wraper
author_rank: Unknown
timestamp: August 09, 2013, 01:52:48 am
content: You could at least write a model, I think this is some Gigabyte UD series. Looks like capacitors because all resistors are smaller on this board. And this picture from the side, do you think people can see much on it? I measured them on a bit similar Gigabyte board, those should be 4,7 uF 0805 caps.

author: Psi
author_rank: Super Contributor
timestamp: August 09, 2013, 02:55:54 am
content: Do a google image search for that model motherboard (and any models similar).Restrict the search results to high resolution images only.You should be able to see if they're resistors or capacitors and maybe even the value if they're resistors and you can read the writing.Or, find the datasheet for that realtek chip and see if it contains a reference layout/circuit diagram.It may show exactly what the components on those pins are.

author: c4757p
author_rank: Super Contributor
timestamp: August 09, 2013, 03:10:19 am
content: Quote from: wraper on August 09, 2013, 01:52:48 amThere is an 0805 resistor in that photo to the left of the barcode sticker.......however, I am pretty sure I see the remains of ceramic capacitor guts stuck there.Thedatasheethas lots of reference schematics. Judging by the abundance of 1uF capacitors in them, I'd guess 1uF, though you should get a closer look and see which pins they go to.

author: SpiderElectronics
author_rank: Contributor
timestamp: August 09, 2013, 07:52:56 am
content: How did they get broken off?Are you sure they are meant to be fitted?What makes you think this will repair the fault?

author: MacAttak
author_rank: Unknown
timestamp: August 09, 2013, 08:27:07 am
content: Looks to be extremely close to this - probably a related board:From this page (I can't read it - I think it is in Japanese?):http://ktyk.seesaa.net/article/100753718.htmlClearly caps. But very hard to say what values.Datasheet:http://www.hardwaresecrets.com/datasheets/ALC889_DataSheet_1.0.pdfThe application circuit doesn't show anything obvious on pins near those pads. But with the photo angle it is very hard to figure out where the traces go.

author: SpiderElectronics
author_rank: Contributor
timestamp: August 09, 2013, 08:35:06 am
content: I think they are most probably DC Blocking capacitors for audio-inputs to the audio chip.They are probably fitted/removed depending on which audio sources are available on the board.

author: Experimentonomen
author_rank: Regular Contributor
timestamp: August 09, 2013, 09:08:05 am
content: They were most likely never populated to begin with, unless you saw them get scraped off by slipping with a screwdriver or such accident.I have a graphics card that looks like components were desoldcered from it but it still works 100%

author: KJDS
author_rank: Super Contributor
timestamp: August 09, 2013, 09:23:14 am
content: I'd be amazed if anything has ever been fitted there.

author: wraper
author_rank: Unknown
timestamp: August 09, 2013, 09:59:28 am
content: Quote from: KJDS on August 09, 2013, 09:23:14 amThere are clearly remains of parts on pads. Those seem to be DC blocking caps because on my board which is similar they are not connected to power rails. So I was able to measure capacitance, all of them are 4.7 uF.

author: Psi
author_rank: Super Contributor
timestamp: August 09, 2013, 10:47:06 am
content: Dont forget the scratch marks visible in the pic. They could be screwdriver slip impacts.Used to see those quite often around cpu heatsink clips.Bit odd for an entire line of caps to be ripped off though, normally the screwdriver would just take out one or two.

author: amyk
author_rank: Super Contributor
timestamp: August 09, 2013, 11:27:20 am
content: Believe it or not I actually found a schematic for a Gigabyte mobo with the ALC880, but it's close enough to show that they're DC-blocking caps. (Is there a common pinout for audio chips or something?)

author: wraper
author_rank: Unknown
timestamp: August 09, 2013, 01:40:56 pm
content: Quote from: amyk on August 09, 2013, 11:27:20 amRealtek chips from the same family have the same or almost the same pinout. ALC650 and 655 are the same, also ALC888 and 889 and others. Even different manufacturers can have same pinout. There are often different model motherboards on the same pcb with different part populated including audio codec.

author: shant
author_rank: Newbie
timestamp: August 11, 2013, 10:52:30 pm
content: awesome! you guys are epic! thanks a lot for the links and information on the role of the caps, they were broke by a person who hit it to the corner of a desk, im not sure if those scratched traces are functional or not, i think the traces need a conductive pen right ?sorry for not posting board model number, its the "gigabyte GA-EP45T-UD3R"

author: wraper
author_rank: Unknown
timestamp: August 12, 2013, 08:08:42 am
content: I don't think they are broken, only solder mask scratched. But if they are then no conductive crap, only soldering them together with thin wire.

author: shant
author_rank: Newbie
timestamp: August 13, 2013, 01:46:18 am
content: can traces be soldered? hmmm, i have to watch how that's done!

author: Psi
author_rank: Super Contributor
timestamp: August 13, 2013, 01:52:18 am
content: Quote from: shant on August 13, 2013, 01:46:18 amYes, but first you have to scrape off the solder mask to revel the copper. Use a blade in the non cutting direction, or a tiny bit of sand paper.Then you can solder them just fine.You might be able to just bridge them with some solder.Otherwise yeah, use a tiny bit of wire (one strand from some multistranded wire). Tin both sides of the track as well as the wire. Then solder it on top.You should be able to confirm conductivity/breaks with a DMM once you have removed the mask.