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Since this is my first question here, I hope this is on topic.

The power supply of one of our old CISCO Aironet 1231G wifi access point failed recently, after a power outage. I think that the power supply failure took something in the AP with it, because even using a known good supply I get nothing when I plug the device in. I opened the device and I think I found the failed component, marked CR1006:

failed component

Considering the blackened pins and PCB traces, I think this is the most likely culprit. I am a relative novice when dealing with electronics though, and I have no idea what this thing is (or rather was). My own research led me to believe that this is some kind of diode, other, more obvious, diodes are also marked as CRxxxx, but I don't see any polarity markings. Here is a second picture which show the markings better:

marking: mirrored "C"ii443 CM

I found nothing about this using Google. Poking it with a multimeter gives me 285 ohms regardless of polarity.

This device is not anything that is really important anymore, and a professional repair is not economical (the AP is at least 8 years old), but I would like to try this repair anyway, as learning experience, and because I dislike throwing repairable equipment away.

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closed as off-topic by Leon Heller, Kaz, Matt Young, Daniel Grillo, Majenko - not Google Jun 18 at 19:11

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See also: Is asking on how to fix a faulty circuit on topic?" – Leon Heller, Kaz, Matt Young, Daniel Grillo, Majenko - not Google
If this question can be reworded to fit the rules in the help center, please edit the question.

    
Did you remove it from the board before measuring resistance? The part could actually be open ("infinite" resistance), while you're measuring the resistance through some other path through the circuit board. Repair questions are topical only if they demonstrate good understanding of the design of the device and are about specific troubleshooting or repair steps. –  Kaz Jun 18 at 17:59

1 Answer 1

This part might be a surge suppressor, which is basically two power zener diodes in series with opposite polarity. If so, then this part being fried is a symptom, not the cause. It may even still be intact, just dissipated a lot of power for a while trying to clamp a voltage to within limits the rest of the circuit can handle. It could also be failed shorted.

You've got little to lose, so try removing the part and see if the unit works without it. If so, it means it is now running correctly, but without the benefit of surge protection this part would otherwise provide. The next surge will blow up even more stuff.

More likely, however, there are other problems. As I said above, this part being fried is more likely to be a symptom of something else going wrong previously, than the cause of the unit not working now. Trying to diagnose and then fix it will be a lot more expensive than just getting a new one.

Modern manufacturing techniques have made electronic device much cheaper than they were a few decades earlier, but the flip side is that they are now harder to diagnose and repair. This makes devices like this disposable when they fail.

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1  
+1 Most likely this is what it is- a bidirectional TVS, since there is no polarity marking. –  Spehro Pefhany Jun 18 at 15:19
1  
Actually, I bet the rest of the board is fine. It looks like this is the first line of defense for the power coming from the external (failed) power pack. I see a common-mode choke and a polyfuse, which probably protected the rest of the board. It might be worth doing a continuity check on the two windings of the choke. –  Dave Tweed Jun 18 at 15:28

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