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Old 08-20-2021, 12:06 AM   #1
shovenose
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Default Ubiquiti US-16-150 Help

Got this dead Unifi US-16-150W, assuming it was the power supply. Alas the PSU and everything looks perfect and the PSU is outputting a solid 53V.

I noticed that upon disconnecting then reconnecting the 4-pin connector from the PSU to the switch's mainboard it makes quite a spark. More than I would expect. So I got curious, took the mainboard out, and found the bottom to be like this.

Is this water damage? Or something else? Should I try to clean it off? Or is it toast?
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File Type: jpg 20210819_230122.jpg (107.5 KB, 25 views)
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Old 08-20-2021, 01:37 AM   #2
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Default Re: Liquid damage or somethign else?

Try cleaning up with denatured alcohol and see if you can clean or use a good flux remover spray I have clean a few boards with a flux remover spray

https://www.mpja.com/Flux-Remover-41...info/30364+MG/

It might be water stains but I not completely sure about this
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Old 08-20-2021, 03:55 AM   #3
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Default Re: Liquid damage or somethign else?

thats residue from water soluable flux,
the factory isnt changing the water often enough.
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Old 08-20-2021, 09:04 AM   #4
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Default Re: Liquid damage or somethign else?

Gotcha, thanks, do you think there is any point in cleaning it? Or is something else wrong with it?
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Old 08-20-2021, 09:43 AM   #5
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Default Re: Ubiquiti US-16-150 Help

Alright, so I did a little testing.

I've attached a couple pictures. I have a solid 24V across the purple caps. This is probably the circuit for the 24V Passive PoE function.

More important, in the other pic across the two points right below the pink dot I have fluctuating 0 to 3.3V. I'm assuming this is a/the problem.

What can I check to see why the 3.3V is fluctuating like that?
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Old 08-21-2021, 12:03 AM   #6
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Default Re: Ubiquiti US-16-150 Help

Most likely something is shorted and the power supply is hiccuping: that is it senses the short, powers down and then tries again...
Some times such a short can be found by a thermal camera (or hand) or you can use a very sensitive multimeter in ohms mode.
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Old 08-21-2021, 12:20 AM   #7
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Default Re: Ubiquiti US-16-150 Help

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Originally Posted by Per Hansson View Post
Most likely something is shorted and the power supply is hiccuping: that is it senses the short, powers down and then tries again...
Some times such a short can be found by a thermal camera (or hand) or you can use a very sensitive multimeter in ohms mode.
Hmm, thing is the power supply is happily at 53.7V with absolutely no fluctuating the entire time.
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Old 08-21-2021, 01:18 AM   #8
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Default Re: Ubiquiti US-16-150 Help

I mean on the secondary side, the 3.3v power supply.
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Old 08-21-2021, 04:57 AM   #9
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Default Re: Ubiquiti US-16-150 Help

Probably there are no shorts on the 3.3V rail. I think there is something else that gets powered from the 3.3V rail that shorts out when powered up. Check the other buck converters. Power the 3.3V up with a bench power supply and see what happens...
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Old 08-21-2021, 11:07 AM   #10
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Default Re: Ubiquiti US-16-150 Help

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Probably there are no shorts on the 3.3V rail. I think there is something else that gets powered from the 3.3V rail that shorts out when powered up. Check the other buck converters. Power the 3.3V up with a bench power supply and see what happens...
Hmm, OK, I'll have to rig something up.

In the meantime, I found this bubble on one of the BCM59111KMLG chips. It's supposedly a 60W PoE controller. Is this normal? Or bubbles=bad?
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Old 08-21-2021, 11:16 AM   #11
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Default Re: Ubiquiti US-16-150 Help

That chip is the problem I’d say.
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Old 08-22-2021, 08:09 AM   #12
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Default Re: Ubiquiti US-16-150 Help

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That chip is the problem Id say.
Thank you, I will see what I can do. I wonder if it's going to be really hard to remove lol.
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Old 08-22-2021, 08:56 AM   #13
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Default Re: Ubiquiti US-16-150 Help

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Originally Posted by shovenose View Post
Hmm, OK, I'll have to rig something up.

In the meantime, I found this bubble on one of the BCM59111KMLG chips. It's supposedly a 60W PoE controller. Is this normal? Or bubbles=bad?
It's dead Jim. That's a burn mark alright. Look also at the discoloration on the PCB around it.

Speaking of removal, depending on the power of your hot air station, you may need to use some sort of preheater or hotplate, that chip is a QFN with a large heat dissipation pad underneath.
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Old 08-22-2021, 01:51 PM   #14
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Default Re: Ubiquiti US-16-150 Help

Shouldn’t be that hard to remove. You can always preheat the board, then take it off with hot air gun.
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Old 08-22-2021, 01:55 PM   #15
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Default Re: Ubiquiti US-16-150 Help

It's easy peasy if you preheat, just don't be surprised if a cheapo chinese SMD rework station alone won't cut it.
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Old 08-22-2021, 06:57 PM   #16
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Default Re: Ubiquiti US-16-150 Help

Quote:
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It's easy peasy if you preheat, just don't be surprised if a cheapo chinese SMD rework station alone won't cut it.
it better be good enough because that's what i ordered haha. i will update once i've tried it.
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Old 08-27-2021, 10:29 AM   #17
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Default Re: Ubiquiti US-16-150 Help

Quote:
Originally Posted by Th3_uN1Qu3 View Post
It's easy peasy if you preheat, just don't be surprised if a cheapo chinese SMD rework station alone won't cut it.
so, i got my cheapo smd rework station and it worked perfectly to remove the chip.

i was hoping i'd get at least some sign of life now that the chip is removed and presumably the short is too.

unfortunately its still dead. what can i check now :'(
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Old 08-27-2021, 11:45 AM   #18
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Default Re: Ubiquiti US-16-150 Help

check for shorted ceramic caps near the dead chip area.
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Old 08-27-2021, 01:45 PM   #19
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Default Re: Ubiquiti US-16-150 Help

Check your wonky power rail. See what it does now?
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