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Fixing the Airrouter you blew up with the wrong wall wart

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wa2ise
wa2ise's picture
Fixing the Airrouter you blew up with the wrong wall wart

You went and done did it, you killed your Ubiquiti Airrouter, because you grabbed the wrong wall wart and overvoltaged it.  And now it's dead. 

Well, there's a good chance that only the little switching DC-DC 5V to 3,3V downconverter circuit blew up. 
 
I removed the dead DC-DC converter chip and its associated inductor and diode, Did a test run with an external 3.3VDC power supply to see if the Airrouter was in fact repairable (that it still worked with this supply), and then used a linear voltage regulator to create the 3.3VDC the router circuits want. I used a regulator that was spec-ed to have low dropout voltage, as the input to output voltage difference isn't that much. And one that can do one and a quarter amps.  I wanted to keep the input voltage at 5V, so if someone plugs a cell phone charger cable or such into the USB jack, it won't get blown up by excessive voltage.  I mounted the regulator's heat sink atop the ethernet jacks.  I used some sheet aluminum I salvaged from an old video monitor, though I probably made it bigger than it needed to be.  In any event, the Airrouter was back on the air!  
 

KD1HA
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Can you share the part number

Can you share the part number for regulator? Thanks

W2TTT
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AirRouter

Bob,. As kas, I dud a more complete job! Hope this works for others! 73, Gordon

wa2ise
wa2ise's picture
I used a LM3940it 3,3v

I used a LM3940it 3,3v regulator.  As that's what I had on hand, that could do the low drop out, from 5V to 3.3V.  And it can take up to 12V input (at least mine did!) Bay Linear https://www.digchip.com/datasheets/parts/datasheet/064/LM3940-pdf.php says 26V, but TI and National Semi says theirs' only 7.5V, but be aware that this voltage will also appear on the USB port.   If I did this again, I'd get the KA278R33 https://www.onsemi.com/pub/Collateral/KA278RA05C-D.pdf regulator, it can take up to 35V input.  Or the LM1085 http://www.ti.com/lit/ds/symlink/lm1085.pdf 3A and max 27V in. 

KD1HA
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Thank you. I have 2 that

Thank you. I have 2 that where dead on arrival from eBay. One AirRouter and one AirRouter HP with the PoE and probably due to the wrong power supply.

Denis

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