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The capacitor that Apple soldered incorrectly at the factory

downtowndougbrown.com

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Re: The capacitor that Apple soldered incorrectly at the factory

#101

Post by 83 »

Filligree wrote: post #60
grujicd wrote: post #58

Earlier quoted context omitted.

Well, until today I didn't even know capacitor can have orientation! So more productive Wednesday than yours. In entry level electronics class I had decades ago it was always treated as a component that works the same way no matter in which direction the current flows.

Ceramic capacitors don't have polarity. Electrolytic ones do. Thing is, electrolytic capacitors have far higher capacitance for their size -- though also higher resistance. It's something to check, but the polar ones should be clearly marked as such.

Bipolar electrolytic capacitors are a thing, I recently had to solder up a handful of them in some audio circuits.

Re: The capacitor that Apple soldered incorrectly at the factory

#102

Post by kevindamm »

nuancebydefault wrote: post #89
grujicd wrote: post #58

Earlier quoted context omitted.

Well, until today I didn't even know capacitor can have orientation! So more productive Wednesday than yours. In entry level electronics class I had decades ago it was always treated as a component that works the same way no matter in which direction the current flows.

Once you have experienced blowing up a reversed elcap you will never forget its orientation. I never understood though what makes it leak current and hence heat up.

There's an aluminum oxide layer as a coating on both the anode and cathode inside the (electrolytic) capacitor. Under forward voltage it will gradually thicken but under reverse voltage it dissolves and causes a short. This increases the temperature which causes hydrogen ions to separate and bubble through the material, increasing pressure within the capacitor package until it bursts.

Re: The capacitor that Apple soldered incorrectly at the factory

#103

Post by blitzar »

xattt wrote: post #68
blitzar wrote: post #50

Earlier quoted context omitted.

> Not sure why we stopped expecting that from electronics. Last years model only does 4k, my eyes need 8k

32K ought to be enough for anybody.

32K is going to look so lifeless and dull after you try 64k.

Re: The capacitor that Apple soldered incorrectly at the factory

#104

Post by robomartin »

Brings back memories…

About 30 years ago I designed my first PCB with frequencies in the GHz range. It was full of challenging transmission line paths with frequencies in the hundreds of MHz and above.

I am still proud of the fact that all of the high speed signals worked as designed, with excellent signal and power integrity (the large FPGA was challenging). Emissions passed as well.

I did, however, screw up one thing: DC

I somehow managed to layout the DC input connector backwards!

These boards were very expensive ($2K), so an immediate respin was not possible.

I had to design a set of contacts to be able to flip the connector upside-down and make the electrons go in the right way.

The joke from that point forward was that I was great at multi-GHz designs but should not be trusted with DC circuits.

Re: The capacitor that Apple soldered incorrectly at the factory

#105

Post by rty32 »

pjc50 wrote: post #90
rty32 wrote: post #88

Earlier quoted context omitted.

[flagged]

It's the sort of mistake that one could make in a PCB design today.

Apparently people can't read.

I don't know which part of "to me" is not clear.

I don't design PCB boards (thus the "useless" word), and the comment was apparently a lighthearted joke in response to another lighthearted joke.

Re: The capacitor that Apple soldered incorrectly at the factory

#107

Post by marcosdumay »

nuancebydefault wrote: post #89
grujicd wrote: post #58

Earlier quoted context omitted.

Well, until today I didn't even know capacitor can have orientation! So more productive Wednesday than yours. In entry level electronics class I had decades ago it was always treated as a component that works the same way no matter in which direction the current flows.

Once you have experienced blowing up a reversed elcap you will never forget its orientation. I never understood though what makes it leak current and hence heat up.

Modern electrolytic caps don't burn like they used to.

The last few times I made a mistake, there wasn't even an explosion, even less a short-circuit. The thing slowly boiled and bubbled or unfolded.

Anyway, it blows up because the capacitor's insulation layer isn't some stable material, it's a tiny oxide layer built over the metal plate by anodization. If you put a high voltage on it with the wrong polarity, you reverse that anodization and short the liquid and the metal electrodes.

Re: The capacitor that Apple soldered incorrectly at the factory

#109

Post by Workaccount2 »

kevindamm wrote: post #99
magic_smoke_ee wrote: post #79

Earlier quoted context omitted.

Electrolytic capacitors are kinda like lead-acid batteries in that they are polarized through manufacturing processes. A voltage is applied in the factory to anodize the anode with a thin oxide layer. For fun, I think it would be possible to buy a quality low voltage cap and reverse the polarity of it in-situ which would remove the anodization from the new cathode and deposit a new layer on the new anode (former cath…

Or much shorter, around two years, if it was part of the Capacitor Plague. https://en.wikipedia.org/wiki/Capacitor_plague#Premature_fai... The normal lifespan of a non-solid electrolytic capacitor of consumer quality, typically rated at 2000 h/85 °C and operating at 40 °C, is roughly 6 years. It can be more than 10 years for a 1000 h/105 °C capacitor operating at 40 °C. Electrolytic capacitors that operate at a lower…

This is also why so many LED bulbs are shit, lots of heat in a small space full of electrolytic caps.
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