Why mark the top of electrolytic capacitors - Page 1
Forum section: electronics / projects

author: nukie
author_rank: Frequent Contributor
timestamp: September 07, 2011, 07:40:32 am
content: Hello all,I have this question where it is more related to manufacturing. I have seen many switch mode power supplies with their top of electrolytic capacitors marked or scribble with a marker pen or some sort. Anyone know why is this done?Google doesn't seems to understand my question.Vincent.

author: Unknown
author_rank: Unknown
timestamp: September 07, 2011, 07:51:10 am
content: It's the first signs of imminent PCB graffiti!In most cases the marks will just signify build or test level. Just a production thing like the scribble in new car engine bays. Why the electros? Simply because they offer the most convenient surface for scribbling.

author: Unknown
author_rank: Unknown
timestamp: September 07, 2011, 07:54:54 am
content: Occam's Razor at work....

author: ejeffrey
author_rank: Super Contributor
timestamp: September 07, 2011, 10:31:30 am
content: QuoteBecause the people doing the assembling and test have poor handwriting?

author: ciccio
author_rank: Frequent Contributor
timestamp: September 07, 2011, 03:02:53 pm
content: We do that because, at the moment of visual inspection, we are more sure that the lady that is doing the inspection has checked for correct polarity.A reversed electrolytic can do a lot of damage (even physical injury) at the moment of powering on for electrical test.Most of the time the electrolytics are installed by hand, being trough-hole, and not by the SMD machine, so an error may always occur.Regards

author: Neganur
author_rank: Unknown
timestamp: September 07, 2011, 09:15:07 pm
content: Repair technicians typically mark components they replace on boards that fail assembly line QA / board tests. It can sometimes help to track a 'repair history'.With those bigger electrolytic capacitors I guess it's the visual inspection's tag, as ciccio suggested.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 07, 2011, 09:37:33 pm
content: I do mark capacitors all the time, when I remove then for testing and reinserting them in a heavy populated PCB.For new devices it could be a mark that those capacitors are really soldered underneath.The large capacitors are 90% hand soldered, and this markings helps in the production line, so to not turn the PCB upside down all the time, just for the soldered capacitors inspection.

author: nukie
author_rank: Frequent Contributor
timestamp: September 08, 2011, 03:20:18 am
content: Interesting, that means test are done manually?

author: Unknown
author_rank: Unknown
timestamp: September 08, 2011, 03:24:33 am
content: Quote from: nukie on September 08, 2011, 03:20:18 amDon't think for a moment that every PCB with a scribble has been tested, or even quality checked.

author: ciccio
author_rank: Frequent Contributor
timestamp: September 08, 2011, 09:43:11 am
content: Quote from: nukie on September 08, 2011, 03:20:18 amWe don't build PC motherboards in the tens of thousands (they are surely tested with Teradyne's or other automated systems), but small lots of audio or industrial control's circuits.We test everything manually, that means that a technician test the correct operation of the circuit, maybe with the help of a dedicated jig that reduces the number of connect-disconnect operations, and after a functional test he makes the eventual adjustments and calibrations.He tests each control's operation, and the audio devices are all retested for "audible noise" and correct operation with music or voice signals.The tested device are sent to burn-in and after it they are re-tested before packaging and delivery.Quote from: Uncle Vernon on September 08, 2011, 03:24:33 amI know that, for cheap and simple products, sometimes they test only a small sample of the batch, but in my case we test everything, twice, and I know that we are not the only ones...Regards

author: vk6zgo
author_rank: Super Contributor
timestamp: September 09, 2011, 08:18:18 am
content: With older equipment,it usually means that a tech chasing a fault has removed & tested the cap.Except for very rare or expensive caps,if I remove them,I fit new ones,but other techs have other ways.VK6ZGO

author: Unknown
author_rank: Unknown
timestamp: September 10, 2011, 02:13:58 am
content: Quote from: ciccio on September 08, 2011, 09:43:11 amI wish everything was still done that way.Sadly it's not just mass market consumer devices that are only sample tested, and its not just cheap devices.+1 to your test regime, say no to the throwaway society today.

author: nukie
author_rank: Frequent Contributor
timestamp: September 10, 2011, 02:48:29 am
content: That's true, the marked capacitors I notice are from high availability server power supplies, industrial robotic power supply, and solar inverters in the order of 10kW.

author: ciccio
author_rank: Frequent Contributor
timestamp: September 10, 2011, 05:47:16 am
content: Quote from: Uncle Vernon on September 10, 2011, 02:13:58 amTo my knowledge most (if not all) of the reputable Companies that operates in our market use the same "test politics".In fact sometime testing become boring, because most of the time, thanks to the quality work of our suppliers doing board assembly, we have better than 99% of success in first operational test.I know that this is not true for some Far East products, priced at about 50% of ours... In this case the operational testing is done by the customer.I think that quality testing (married obviously with quality design) add a lot to product's life length.Days ago I checked an intercom power supply that was made in 1985 by myself (then I was a single person operation) , and it needed only cleaning an some screw tightening.The problem (according to my accountant) is that this longevity precludes new sales...

author: Simon
author_rank: Unknown
timestamp: September 10, 2011, 08:02:33 am
content: Quote from: ciccio on September 10, 2011, 05:47:16 ambut it gets you a reputation that gets you more sales, I wish my company thought like that. A friend of mine takes radiators out of cars 70 years old that are made by the company I work for. But nothing made today will still be working in 70 years!

author: Zero999
author_rank: Super Contributor
timestamp: September 10, 2011, 08:50:38 am
content: Quote from: Simon on September 10, 2011, 08:02:33 amIt depends on your market. For a premium product which people expect to have a long life, you'll get more sales deigning for longer life but if it's something which people replace fairly often, designing for longer life just pushes up costs.