Why mark the top of electrolytic capacitors

[nukie]

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.

[Uncle Vernon]

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.

[HLA-27b]

Occam's Razor at work....

[ejeffrey]

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?

Because the people doing the assembling and test have poor handwriting? 

[ciccio]

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

[Neganur]

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.

[Kiriakos-GR]

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. 

[nukie]

Interesting, that means test are done manually?

[Uncle Vernon]

Interesting, that means test are done manually?

Don't think for a moment that every PCB with a scribble has been tested, or even quality checked.

[ciccio]

Interesting, that means test are done manually?

We 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.

Don't think for a moment that every PCB with a scribble has been tested, or even quality checked.

I 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

[vk6zgo]

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

[Uncle Vernon]

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.

I 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.

[nukie]

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.

[ciccio]

I 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.

To 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...

[Simon]

The problem (according to my accountant)  is that this longevity precludes new sales...

but 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!

[Zero999]

The problem (according to my accountant)  is that this longevity precludes new sales...

but 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!

It 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.