Meanwell PSU blown - Page 1
Forum section: electronics / repair

author: thedude8888
author_rank: Newbie
timestamp: June 28, 2017, 05:57:56 pm
content: Hey everyone, i messed up a little yesterday.I noticed my Meanwell NES-350-12 psu was giving my finger a little current when i was touching it on the metal enclosure.http://www.meanwell.com/scripts/resource/pdfJS/web/viewer.html?f=NES-350&pdf=NES-350-SPEC.PDFI looked at it for 15 mins thinking fuk, and then i remembered reading something online about people having problems with the psu, if the 110/230V slide button was set wrong. I was already on 230V, as i should, but then out of nowhere i put it on 110V and powered ON.There was a bang and a lot of smoke. So now i have blown capsI think. Nothing else seems to be burnt or anything.Do you think it would be fixable with just replacing the caps? Or would it be more easy to just buy a new one for 50 bucks?And what would your guess be to the problem with the psu enclosure, giving off current and making your heart beat a little worse when touching it? It actually worked still worked good with the zapping, but it was just kindda there suddenly. Wires were all still connected good. Just a little zapping. But then i went and did the bad thing.Do you think it is fixable?

author: thedude8888
author_rank: Newbie
timestamp: June 28, 2017, 06:01:28 pm
content: And would also guess that i need to replace the small fuse. 8A250V i think it was. Is this true?

author: wraper
author_rank: Unknown
timestamp: June 28, 2017, 06:28:49 pm
content: Quote from: thedude8888 on June 28, 2017, 05:57:56 pmThe problem was you did not connect the ground wire. There was no failure. Just a little bit of current flowing through the noise suppression capacitors connected between mains voltage and enclosure. It should be fixable, however the quantity of failed parts depend on your luck. I don't see any capacitors obviously blown on the pic. So YMMV if they were blown or not. Almost anything on the primary side could fail. PWM controller, mosfets, rectifier, capacitors...

author: alm
author_rank: Super Contributor
timestamp: June 28, 2017, 06:42:15 pm
content: I would definitely check the primary side semiconductors (rectifiers, FET) for opens/shorts. As for the need to replace the fuse, that should be easy to test (does it measure as a fairly low resistance or open circuit).

author: Armadillo
author_rank: Super Contributor
timestamp: June 28, 2017, 06:46:10 pm
content: Terminal 3 should be connected to Ground Or Earth.Note Check also that terminal 2 is the Neutral, you know sometimes it get mixed around with live.

author: rg58
author_rank: Regular Contributor
timestamp: June 28, 2017, 07:38:33 pm
content: Yes, it is probably fixable, but if you are not familiar with electronics as it sounds,I would highly advise you for your own safety to stay away from any repair attemptsof switched power supplies! We are talking about voltages of nearly 400V DC here that can still be present for up to several minutes even if the PSU is powered OFF.DANGEROUS!Apart from that, those things are sometimes not trivial to fix and can be quite stubburn. Usually the switching MOSFET is gone, maybe the IC as well, diodes, resistors can be broken too without you seeing it from just looking at them. If you are lucky it really is only the fuse, but I doubt it. You can check the fuse with an Ohmmeter to see if the resistance is near to ZERO Ohms. If it has a high resistance (Ohmmeter not showing anything) then the fuse is gone and needs to be replaced. You can try putting in a new fuse of the same rating, close the metal case (safety!!) and turn it on - AT YOUR OWN RISK! It will most likely make a big BOOM and smoke starts to come out.To make this work I would go through a lot of parts with my multimeter and test them one by one, investing at least 1-2 hours of my time before even attemping to turn it on CAREFULLY with some kind of protecting on the mains side (limiting the mains current and voltage). As I do not think that you have enough professional experience with electronics, I would recommend you to buy a new one. You may still sell the broken one on eBay for parts to someone with more experience in electronics.

author: WastelandTek
author_rank: Frequent Contributor
timestamp: June 28, 2017, 08:03:19 pm
content: Quote from: thedude8888 on June 28, 2017, 05:57:56 pm

author: Electro Detective
author_rank: Super Contributor
timestamp: July 03, 2017, 02:01:26 am
content: Quote from: thedude8888 on June 28, 2017, 05:57:56 pmVote #1 for a new one at 50 bucksThe parts may cost you $55Get an identical unit, and the blown one can be a future parts donor (once you test the parts first)In time you may decide to repair the blown one using the good one as a reference.It's a $50 no brainer decision I reckon