Recommended stock of low-ESR caps for monitor / TV SMPS repairs? - Page 1
Forum section: electronics / repair

author: Delta
author_rank: Super Contributor
timestamp: December 07, 2015, 01:47:05 pm
content: If one were to be embarking on collecting and hopefully repairing LCD TVs and PC monitors, what range of values of low-ESR caps should I keep on hand?Cheers!

author: Ian.M
author_rank: Super Contributor
timestamp: December 07, 2015, 02:31:30 pm
content: Maintaining a large stock of good quality low ESR caps will kill your margins due to the wide range of voltage ratings and form factors used.If you want to get this right, you need to log every part used to the job ticket in a searchable database so you can make intelligent stock control decisions. If you are going down that road, you might as well insist on adding a brief fault description refined by the service tech, including component designators so it can be used to identify stock faults.We didn't do the database thing properly and used to operate a policy of buying one part for the set and one for stock unless the part was grossly expensive. Generic dead parts were chucked in a jar by type, and when the jars got full enough, they were sorted to identify commonly used parts to stock. If it was really cheap, we'd usually go the first price break quantity if we thought it would be a common part. We'd typically put in two or three orders a week for next day delivery. If you've got the volume you can go to daily orders.

author: Delta
author_rank: Super Contributor
timestamp: December 07, 2015, 06:17:18 pm
content: Whilst I genuinely appreciate you advice Ian, I think you may have over estimated the size of my planned operation! I'm just talking about buying a few pints for the bloke who works at the council dump (sorry, "recycling centre", and collecting a few TVs a week.What caps should I keep on hand so I can fix stuff immediately, rather than order specifically to replace like for like?

author: SeanB
author_rank: Super Contributor
timestamp: December 07, 2015, 06:36:32 pm
content: Typically you will need 1000uF 16v capacitors, preferably on a 6mm pitch ( or close to that) so they will fit most boards. Some 1000uF 25V ones as well, and a similar number of 1000uF 10V. Then some 470uF 35V will be useful. The 1000uF can be used to replace any from 560uf to 1500uf reasonably well, and you need the different voltages because the cans get longer or larger with increasing voltage. Some 82uF 450V ones will be used for the primary side, and a few 100uf 63v ones as well, used for the startup supply. That will cover a large number of the most common values, and will at least allow the set to start up.

author: Ian.M
author_rank: Super Contributor
timestamp: December 07, 2015, 06:54:57 pm
content: I'd add a selection of smaller ones in the 1uF to 100uf range (1, 2.2, 4.7 in each decade), all 63V. The problems start however when the board has SMD electrolytics, and you try to bodge on thru-hole ones and end up ripping off traces. There is no substitute for the right part for the job.

author: Shock
author_rank: Super Contributor
timestamp: December 08, 2015, 12:34:43 am
content: Do you really mean low ESR, don't confuse a cap that failed out of spec because it was a cheap/poor quality, underrated for the circuit or was sitting right next to a heat source. You don't necessarily need low ESR caps you need caps that are going to not crap themselves when warm or left on in a powered circuit for a few years.I would just use a known name brand (as opposed to notorious), if you look at element14 or mouser you will find most of the better ones. A quick google will confirm if it's junk or a defective series. Then make sure it's voltage and temp is suitable if the design was in question and you're done.

author: wblock
author_rank: Regular Contributor
timestamp: December 08, 2015, 04:24:21 am
content: Quote from: Shock on December 08, 2015, 12:34:43 amSwitching supplies typically do need low-ESR caps. GP caps will fail in a matter of months. As far as stock, the general rule is that what is needed is pretty much what is not on hand. For low quantities, probably best to order what is needed, but get a few extras each time.

author: Shock
author_rank: Super Contributor
timestamp: December 08, 2015, 07:01:32 am
content: Yeah what I mean is ESR is not the only factor you have to take into consideration. Seen plenty of good caps huddling around a heatsink like it's a camp fire.