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Old 04-17-2016, 12:38 PM   #1
Per Hansson
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Default Dell PowerConnect 2716 and ADP-40VP PSU recap

This switch power LED was lit red and some ports with cables not even in them where lit yellow after a power outage, not a good sign...

I checked the caps and they visually looked ok and even tested good in circuit.
The startup and bulk caps where replaced in it some years ago.

I first desoldered all 1000F 6.3v Taicon HD 8x16mm capacitors on the switch and tested them out of circuit and then it became obvious what the problem was:
Their ESR ranged from 0.11 > 0.98!
So I replaced them with Rubycon ZLJ 1000F 10v 8x20mm caps (10000 hours lifetime!)

Next I checked the ADP-40VP PSU where the caps also had measured ok in circuit.
Not so out of circuit: The Ltec LZG 2200F 10v 12.5x20mm ranged in ESR from 0.05 to 0.80 & the lone Ltec LZG 1500F 10v 10x23mm measured 0.05.
They got replaced with Panasonic FR 2200F 16v caps in matching dimensions and the lone 1500F cap got replaced with a Samxon GT 1000F 25v cap in matching dimensions.
I checked ripple before and after the recap and it was an improvement at idle.
Though with a load the ripple is around 80mV which is not so great... (Did not check the load ripple before the recap).

I can't really fault the original caps, the switch is 10 years old now and has been running pretty much 24/7, but with the new caps rated for 10000 hours I'd be surprised if they fail within my lifetime
I also saw when Googling this PSU that there exists a direct replacement from Artesyn: NLP40-7605J which RS, Farnell, Mouser and Digikey stocks.
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Old 04-17-2016, 01:35 PM   #2
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

Is it working now?
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Old 04-19-2016, 12:05 AM   #3
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

Nice job, Per!

That PSU should indeed last a very long time. The only thing I am concerned about is the heat/burn marks under the primary bulk cap. Does the PSU run hot, especially in that area? If yes, I wonder why only the primary side and nowhere else. SMD snubber network on the solder side, perhaps?

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Is it working now?
I'm guessing so. If he was able to test it and all.

Last edited by momaka; 04-19-2016 at 12:06 AM..
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Old 04-19-2016, 01:38 AM   #4
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

I have an identical PSU in a Dell PowerConnect 2724.
It also has a heat mark in the same place, a bit worse.
The big primary cap on mine was visibly bulging, so i wonder if that would cause the resistor to heat up ?
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Old 04-19-2016, 06:06 AM   #5
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

Maybe. That capacitor may slowly be turning from a capacitor into a resistor into a virtual piece of 0-gauge wire bridged across the 2 capacitor terminals.
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Old 04-19-2016, 01:54 PM   #6
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

momaka: Yea the heating on the primary side was caused by the primary capacitor failing, which is a very common failure mode in this PSU.
There even exists "rebuild kits" on eBay for it...

TechGeek: Heh, left that part out didn't I? Yea it's working fine after the recap
I was a little skeptical at first because I know from Linksys routers that when ports are lit randomly without a cable plugged in it's usually CPU damage...

diif: I think the failing bulk capacitor causes the diodes to work too hard with resulting overheating.

Edit: would have been nice to replace the two SMD caps as well but have no idea what their ratings are. (Anybody have some idea bar the obvious 16v 100F?)
For sure they can't have had an easy life when all the other caps around failed...

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Old 11-14-2017, 03:09 PM   #7
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

Quote:
Originally Posted by Per Hansson View Post
would have been nice to replace the two SMD caps as well but have no idea what their ratings are. (Anybody have some idea bar the obvious 16v 100F?)
For sure they can't have had an easy life when all the other caps around failed...
Curiosity took the better of me:
Looking in the datasheet for the AMS1505 voltage regulator it seemed like the lower the ESR the better.
So I bought some with 0.45Ω ESR & 197mA ripple.
They even have 2000h endurance at 125C.
Switch seems happy enough with them

Anyway the old ones where the shocker:
Bop parker ESR meter does not see a cap at all.
My "component tester" says one has 200F capacitance and the other 300F.
The ESR is listed as 0.14K or 140!
And the leakage is at around 10%
Dear god, poor switch, how did it survive this abuse?!

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Last edited by Per Hansson; 11-14-2017 at 03:31 PM..
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Old 11-15-2017, 08:58 PM   #8
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Default Re: Dell PowerConnect 2716 and ADP-40VP PSU recap

Quote:
Originally Posted by Per Hansson View Post
Anyway the old ones where the shocker:
Bop parker ESR meter does not see a cap at all.
My "component tester" says one has 200F capacitance and the other 300F.
The ESR is listed as 0.14K or 140!
And the leakage is at around 10%
Dear god, poor switch, how did it survive this abuse?!
Nice work, Per!

Wow, those SMD caps for sure are dead. My component tester typically shows caps 0.15k for near open-circuit caps... with the occasional Sacon FZ being interpreted as a film/ceramic cap with just a few picoFarads of capacitance. And the truly open-circuit caps show as "no, unknown, or damaged component".

That said, it is indeed interesting how the switch managed to survive with those caps, considering they appear to be connected to a buck regulator. After all, we know what happens to those LinkSys WRT54G routers when they have really bad caps.

However, it seems that not all buck regulator circuits are intolerant of bad caps. Case-in-point, your switch. But I've also had a lot of XFX video cards with completely open-circuited Sacon FZ filter caps and both the RAM and GPU survived.

Last edited by momaka; 11-15-2017 at 08:59 PM..
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