I destroyed some SMD caps....Help! - Page 1
Forum section: electronics / beginners

author: melrel
author_rank: Contributor
timestamp: April 10, 2011, 08:03:38 pm
content: Hi Guys here's the pic of the destroyed caps. I wrecked them with a screwdriver whilst trying to remove a hybrid module on a plazma TV Z-sus board. I didn't see them because they were hidden under a heat sink. Please can someone tell me what I need to do to order these parts. All these capacitors in this row have an ESR of .5 or thereabouts. I measured them and I think they are of the 0805 variety (10ph - 4.7uf). I unsoldered one of them and my tweezer DMM won't measure nf. Even if I knew the value of the cap how do I know the voltage and wattage requirement for a replacement? This problem is really getting to me. I have been all over the world trying to get an answer. So far I haven't been able to get hold of a schematic - it's an LG 42PX5d Plazma TV and the Z-sus board number is 6871QZH056B. If I can't fix it soon my dear wife is going to hoof the lot out.

author: Zero999
author_rank: Super Contributor
timestamp: April 10, 2011, 08:35:15 pm
content: It's very had to get schematics for modern TVs as they're generally not worth repairing and if they are few technicians bother to debug down to component level, the usual answer is just to replace the entire board.You could try replacing them with somethng generic like 100nF (typical for decoupling) then if it doesn't work replace the board.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 10, 2011, 08:36:34 pm
content: they seem to be all in parallel, maybe a noise remover? are you sure the tv wont turn on without these? try any smaller smd caps you can get. maybe they can work.

author: quirmche
author_rank: Contributor
timestamp: April 10, 2011, 08:41:13 pm
content: eBay has the whole board. Judging from your grammer I suspect you are from the UK or the like. Here is a link to your board. I suggest get the board, pop it in and be done with it. Believe me you'll be glad you did!!!http://cgi.ebay.com/LG-42PC1DA-42PX5D-YSUS-6871QYH053B-6871QYH053A-/220761248616?pt=LH_DefaultDomain_3&hash=item3366655368

author: joelby
author_rank: Frequent Contributor
timestamp: April 10, 2011, 08:51:12 pm
content: Power rating is mostly based on the package, so as long as you get the same package I wouldn't worry. If you don't know what the voltages on the board are, just get the highest rated capacitors you can buy.

author: Unknown
author_rank: Unknown
timestamp: April 10, 2011, 09:14:24 pm
content: What else is around that area? They look as if they are stitching two copper fills together at high frequencies. Could be an EMC measure, in which case the caps might be of different value. Is any of the two fills ground?The obvious thing is to measure a few from that row (go to a local electronics store, they should have something that measures small caps). This looks like 0805. If they are all the same then buy 5 of those. If not, measure the last ones from the complete row next to it.Apart from that you can leave it as it is, I doubt it would have any real effect on operation, remember they have large tolerances. I see another row next to that, you can desolder one from there and bring it over to balance things out a bit.£65 for 3 0805s sounds like a terrible waste. Also, be careful with the ebay board, there seem to be different revisions if you just google the board number.

author: Simon
author_rank: Unknown
timestamp: April 10, 2011, 09:16:00 pm
content: I'd say replace the board if you can, otherwise your wife has the best solution

author: Unknown
author_rank: Unknown
timestamp: April 10, 2011, 09:17:59 pm
content: Oh come on Simon! We are not like that, we fix things that break!

author: Hypernova
author_rank: Unknown
timestamp: April 11, 2011, 12:43:06 am
content: Quote from: Hero999 on April 10, 2011, 08:35:15 pmEarly Feb I fixed my landlord's Samsung TV by replacing the caps which popped. $6 for a pack of caps from RS vs $99 for what the repair man quoted her just to come out and look it over, I found the problem within 20sec of opening the back panel.

author: Simon
author_rank: Unknown
timestamp: April 11, 2011, 05:55:20 am
content: Quote from: Alex on April 10, 2011, 09:17:59 pmWell i'm talking about it getting fixed faster than the wife can get rid of it(Having just picked up a radiogram for my dad off some poor old man who's wife decided they didn't have room for it)

author: melrel
author_rank: Contributor
timestamp: April 11, 2011, 06:56:27 am
content: Thanks all you guys for taking the time to reply to this. I know That Simon is probably right with his suggestion but I am not doing this for business. I have just retired and find this electronics sooooooo cool to get into. But my sentiments are with Alex - I really want to get down to component level and find out what's going on. I'll take your suggestion and trot on down to Maplin and see if I can replacements. The other thing about this is that I have already purchased the intelligent power module (underneath the sink) and apparently that's the usual thing to fail on this board. It was a hell of a job to get off the board until I was introduced to Chip Qwik SMD rework solder. The module cost about £35 so I am committed to get this thing going. Thanks to all of you again for this. I'll keep you informed of progress. Kind regards Robert

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 11, 2011, 07:58:44 am
content: if you cannot fix it, buy the board.

author: Unknown
author_rank: Unknown
timestamp: April 11, 2011, 08:57:39 am
content: Happy cap rolling! lol

author: Zero999
author_rank: Super Contributor
timestamp: April 11, 2011, 04:53:56 pm
content: Quote from: melrel on April 11, 2011, 06:56:27 amI've not seen SMT capacitor in Maplins for years.There's Farnel, RS Components, Rapid, Digikey etc. but they all charge a lot for delivery on small orders, unless you have a business account.

author: Time
author_rank: Frequent Contributor
timestamp: April 11, 2011, 07:04:32 pm
content: looks like power supply decoupling to me. I bet you can just arbitrarily replace them and be good to go.

author: melrel
author_rank: Contributor
timestamp: April 11, 2011, 07:22:35 pm
content: OK, well I'll have to check up on line and see if they do sell SMD components. Thanks Hero999, you might have saved me a journey there. When you say arbitrarily Time, do you mean any 0805 cap? I do get the impression from you guys that the cap values are not that important. This is the stuff I need to learn. So why have the designers opted for a load of low value caps in parallel in preference to selecting a larger single cap. Surely it can't be just a space-saving exercise. The PCB machine must have to do a heck of a lot more travelling around the board sticking these things everywhere. Don't get it!

author: Time
author_rank: Frequent Contributor
timestamp: April 11, 2011, 07:31:41 pm
content: .01, .47, or .1 would be good.Here is some fun reading:http://download.micron.com/pdf/technotes/TN0006.pdf

author: Time
author_rank: Frequent Contributor
timestamp: April 11, 2011, 07:35:53 pm
content: Quote from: melrel on April 11, 2011, 07:22:35 pmThe amount of parasitic inductance and resistance is reduced by using individual caps in parallel. If you look at the impedance vs. frequency curve of the parallel combination it gets closer to ideal with the more you have. Its a practice you commonly see in use on the power supply rails of some types of RF ICs.

author: Zero999
author_rank: Super Contributor
timestamp: April 11, 2011, 07:42:04 pm
content: 100nF is the most common decoupling capacitor value but to get better frequency response engineers will put lower and higher values in parallel, so you might get 100pF, 1nF, 10nF, 100nF and 1uF all connected in parallel with the lowest value situated closer to the source of the high frequency noise.

author: melrel
author_rank: Contributor
timestamp: April 11, 2011, 09:21:45 pm
content: Thanks Time and Hero999, I wish I could just download your knowledge into my head. I will read the article Time, it has already explained that by using smaller caps in parallel the ESR is lowered and therefore the inductance. This is so interesting. Sex on a stick as Dave would say. This provokes me to ask you a shed load of stuff on the same subject but I will resist doing so as I know your time must be valuable. Best regards Robert