Trying to fix my UniFi USW 48 power supply

[Beardz]

So I got the USW 48 switch and it went boom. On closer inspection, I found out that the 68uf 400W capacitor on the power circuit is swollen and it is the probable cause for burning out the fuse and resistors r20 to r24. I have no problem finding the capacitor or the fuse but the resistors are so burnt that I have no clue what they are. I'm hoping that someone could help me to find the replacement components

[Renegade042]

I hope you are the world's top electrician, cause i'm almost positive 5 out of 4 youtubers recommend against

fixing your own PSU...

[LIGISTX]

5 minutes ago, Renegade042 said:

I hope you are the world's top electrician, cause i'm almost positive 5 out of 4 youtubers recommend against

fixing your own PSU...

As long as you know what you are doing, its fine. If you do not know what you are doing (which you will either know you know what you are doing, or you will know you do not know what you are doing), do not ever open up a PSU.

 

Do not pretend to know what you are doing either. If you know what you are doing, you know what you are doing, likely from electrical engineering cources in school, or being an electronics assmebly technitian etc. 

26 minutes ago, Beardz said:

So I got the USW 48 switch and it went boom. On closer inspection, I found out that the 68uf 400W capacitor on the power circuit is swollen and it is the probable cause for burning out the fuse and resistors r20 to r24. I have no problem finding the capacitor or the fuse but the resistors are so burnt that I have no clue what they are. I'm hoping that someone could help me to find the replacement components

Good luck... I am not sure where that data would be, or if its even published anyway. I may suggest checking out https://forum.level1techs.com/ as folks there will be much more in the weeds and may even have a switch opened up they can just read the resistor color codes or values off of for you. Folks here may as well, but there is "less noise and more signal" on level1techs for things this technical, if you catch my drift. Potentially also Lawrence Systems forums as well, lots of folks there run Ubiquity gear as well.

[johnt]

10 minutes ago, Renegade042 said:

almost positive 5 out of 4 youtubers

They are definitely the most qualified bunch to give advice 

[Renegade042]

7 minutes ago, johnt said:

They are definitely the most qualified bunch to give advice 

Well lets just assume that any advice Linus gives comes from writers who did their research

and maybe talked to an expert or two before they recorded their video

[Beardz]

Thanks for the input. I have a degree in information electronics. I tried to measure the components but they are so badly fried that I get no reading from them and also the text on top of the component is unreadable. I was hoping that someone has a similar switch and could look inside and identify the components

 

I will ask around from other forums also.

 

"Don't worry brah.. i know what I'm doing"

[Alex Atkin UK]

3 hours ago, Beardz said:

So I got the USW 48 switch and it went boom. On closer inspection, I found out that the 68uf 400W capacitor on the power circuit is swollen and it is the probable cause for burning out the fuse and resistors r20 to r24. I have no problem finding the capacitor or the fuse but the resistors are so burnt that I have no clue what they are. I'm hoping that someone could help me to find the replacement components

Just because the capacitor was swollen, doesn't mean that was the cause, it could also be a symptom of a deeper problem.

 

I've replaced a decent number of capacitors on routers and other devices where I had nothing to lose, but when it comes to PSUs its a big nope from me.  Though it sounds like you have a better chance of understanding the circuit than I would, so fair enough.

 

I just don't think its worth risking destroying the switch (assuming it isn't already) over.

[johnt]

7 hours ago, Renegade042 said:

Well lets just assume that any advice Linus gives comes from writers who did their research

and maybe talked to an expert or two before they recorded their video

That's exactly what we discovered from the last debacle a few months ago...

 

You need to do your own research at times and get your hands dirty with your own projects. I'm not suggesting everybody open their own PSUs and start replacing components willy nilly. But it isn't as hard or as complicated as the tubers make it sound. There are a lot of capable people in this world.

[johnt]

What happened to the warranty?

[Beardz]

Its secondhand i wound a psu from ebay but the problem is that its on the other side of the globe and with shipping i might just buy a new one

[Alex Atkin UK]

19 hours ago, johnt said:

That's exactly what we discovered from the last debacle a few months ago...

 

You need to do your own research at times and get your hands dirty with your own projects. I'm not suggesting everybody open their own PSUs and start replacing components willy nilly. But it isn't as hard or as complicated as the tubers make it sound. There are a lot of capable people in this world.

While replacing a few capacitors is not complicated, knowing they were actually the cause of the problem and not a symptom of a greater problem elsewhere IS complicated.

[johnt]

6 hours ago, Alex Atkin UK said:

While replacing a few capacitors is not complicated, knowing they were actually the cause of the problem and not a symptom of a greater problem elsewhere IS complicated.

Diagnosis is truly an art. But the fear mongering on this forum just for opening your PSU is on another level. Last year I was in an argument for swapping my PSU fan that was making a very loud bearing sound under load. It was a five minute job with a simple mini fan connector. It's not helpful to tell people they are going to die if they open their PSU. That doesn't fix problems... just creates e-waste. I could have easily bought a new PSU to get rid of the noise but it was a $20 fan.

[Alex Atkin UK]

19 hours ago, johnt said:

Diagnosis is truly an art. But the fear mongering on this forum just for opening your PSU is on another level. Last year I was in an argument for swapping my PSU fan that was making a very loud bearing sound under load. It was a five minute job with a simple mini fan connector. It's not helpful to tell people they are going to die if they open their PSU. That doesn't fix problems... just creates e-waste. I could have easily bought a new PSU to get rid of the noise but it was a $20 fan.

Very true, but you have to accommodate the lowest common denominator.  There's a lot of people out there willing to "have a go" at fixing things they really shouldn't.  Even ignoring the dangers, the risk that if you get it wrong you can fry everything connected to the PSU should not be taken lightly.  Even if the PSU appears to work fine, if you replace the components wrong it could be running out of spec causing damage over time.

Even a dry joint in the wrong place on a poorly designed PSU (or one where the Y capacitors have also failed) could cause spikes on the entire mains circuit, damaging devices not even connected to the PSU itself.

 

As someone who once accidentally touched the PCB of a running PC PSU (old PSU before they put isolation layers between the PSU case and the PCB plus had a huge hole that slot into the case), I'm a lot more wary.  The current had a direct path to ground through my fingers and hand but my entire left arm was numb for hours.  I was very lucky.