SMPS Laptop Adapter Outputs 3-4V instead of 19V - Page 1
Forum section: electronics / repair

author: penmarker
author_rank: Contributor
timestamp: September 17, 2017, 12:57:38 pm
content: My laptop adapter had stopped working one day and using a multimeter I measured the output to have gone down from 19V to 10V, and it keeps going down to 3V or 4V and drifts up and down.Since I do have a replacement backup adapter, I decided to open it up and attempt a repair. They have several no name brand capacitors with no indication of damage or anything. I decided to replace all of them anyway and ordered from Element14. Because of the casing limitation I had to choose the ones that will fit instead of selecting low ESR parts. I believe modern and original electrolytics will have low ESR anyway but if I may be wrong so please correct me.One question I have is, my PCB has a blank X capacitor placeholder. There is a Y capacitor so it is a little weird to see it having a Y without an X.I'm not too familiar with SMPS and I've only came across the X/Y capacitors from recent searches.Should I be worried about the absence of X caps?

author: SMdude
author_rank: Frequent Contributor
timestamp: September 17, 2017, 04:32:11 pm
content: Have you tested it with the output cable disconnected? I have found a few times that the cables have been internally broken near the end and in some cases shorting out.In terms of the "missing" cap, well it was probably a design option, just in case they needed it for EMC compliance or something.

author: stj
author_rank: Super Contributor
timestamp: September 17, 2017, 05:42:37 pm
content: what he said, check the voltage at the charger pcbbtw, nice job getting in - some of those cases are a bitch to open.

author: Armadillo
author_rank: Super Contributor
timestamp: September 17, 2017, 09:14:35 pm
content: I don't think the adapter is the original adapter. The input line noise filtering and EMI shielding are non existence, line choke missing etc. More likely a piece of cheap adapter of unknown origin. Therefore there is not a need to be concerned with X or Y capacitors unless your neighbours complain of line noises from you. But likely they wouldn't notice it anyway, and if they ever did, they would more likely blame the Grid.

author: amyk
author_rank: Super Contributor
timestamp: September 17, 2017, 09:25:15 pm
content: In particular, check the cap which supplies power to the controller IC, and yes, low ESR is a requirement and not all caps are today. Visit badcaps.net for (much) more information.

author: wraper
author_rank: Unknown
timestamp: September 17, 2017, 10:00:40 pm
content: Throw this piece of crap into waste bin. It's non original or counterfeit charger. Distance between primary and secondary is tiny, this crap is simply dangerous.

author: penmarker
author_rank: Contributor
timestamp: September 18, 2017, 03:40:02 am
content: Quote from: SMdude on September 17, 2017, 04:32:11 pmNo I haven't because I don't think that's the case here. What tipped me off was the LED power indicator was also pulsing and very dim.Quote from: stj on September 17, 2017, 05:42:37 pmThis one was really quite a bitch too, but I managed to crack it open with a flat blade screwdriver.There was a lot of hard glue inside to keep it closed, I'm just glad I didn't rip anything off the board especially the BR and the regulators since they're stuck to the metal cage for heatsinking.Quote from: Armadillo on September 17, 2017, 09:14:35 pmYes you're right. My bag along with some external HDD, mouse, laptop adapter, etc was stolen and I only had my laptop on my person at that time. The original laptop adapter was very robust, the brick is big, wires are thick and the connection is tight and inspires confidence.This adapter is a Grenosis universal laptop adapter. It comes with an array of output jacks for different laptop brands and output voltage.There is actually shielding, I took it apart. The shielding is two parts - one stuck on the board as heatsink for the regulators (with thermal paste) and the other was stuck to the adapter brick body. They close like a clamshell.I've actually had bought 3 different adapters, the other 2 was pretty shit. They both had some leakage that I can feel on the laptop body. This current one that I opened, even though looks pretty shit, is actually the best out of 3. It feels good in the hand too when I pick it up, feels solid and have that hefty weight to it. No current leakage on the body that I can feel.But yeah there's no perceivable noise when the laptop is plugged it.Quote from: amyk on September 17, 2017, 09:25:15 pmThanks a lot, they are a good source of information.Quote from: wraper on September 17, 2017, 10:00:40 pmYes it's a 3rd party charger.I don't have any better one at the moment, and I went to Acer store for an original adapter, they said they don't sell them, only laptops.I looked through eBay and none of the "genuine" and "original" adapters look like it.

author: wraper
author_rank: Unknown
timestamp: September 18, 2017, 12:03:40 pm
content: Quote from: penmarker on September 18, 2017, 03:40:02 amCheck authorized Acer service centers. They should sell them.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 18, 2017, 03:51:45 pm
content: Poubelle...Envoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 18, 2017, 05:02:56 pm
content: Quote from: perieanuo on September 18, 2017, 03:51:45 pm+1

author: Armadillo
author_rank: Super Contributor
timestamp: September 19, 2017, 01:42:49 am
content: Everyone is entitled to their opinions so just relax....Your question was on X cap, so I assume you have repaired the adapter? If not, just shake the component leads and look out for dried out poor solder joints. Wraper was right, distance kind of close, so be aware of it ok?

author: penmarker
author_rank: Contributor
timestamp: September 19, 2017, 10:33:52 am
content: Quote from: blueskull on September 18, 2017, 03:49:54 amIt's the same voltage as most laptop adapters at 19V, but the current rating is supposed to be 4.2A. Most adapters are only rated at about 3.42A however.Quote from: wraper on September 18, 2017, 12:03:40 pmI'll try and see within the week if I could take a long lunch break from work.Quote from: carl_lab on September 18, 2017, 05:02:56 pmI'll be sure to bin it after I get a replacement.But I must say it worked for the past 1 1/2 years.Quote from: Armadillo on September 19, 2017, 01:42:49 amIt's okay, I do understand.I haven't repaired it yet, still waiting for the 150uF cap to arrive. Other than that suspected cap, everything else looks fine. No burnt smell or cold solder joints.Does anyone has an example of a good laptop adapter board? I'm not too familiar with how they should look like. SMPS is very new to me.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 19, 2017, 06:01:38 pm
content: Quote from: penmarker on September 19, 2017, 10:33:52 amWe have sell about 2-5 every day in paris in a tiny boutique.about 10% returns in the first month.some of them worked 1-2 years.but here becomes interesting we had also reports in fact scandals with burned motherboards.a mobo was more then 130 euros at the time...So judge for yourself if for 40-50 bucks you put in danger your board.me I say poubellewith no disregard to you and the readers.Same thinking goes to generally power supplies quality and repair.never forgot the board attached is more expensive and put also your time.Smps like that one I repaired more than 200 -I had to,not by conviction...doesn't worth the time spent,in the end you still have a sh...tty transformer with low window size at limit for power needed and so on..Regards,PierreEnvoyé de mon iPad en utilisant Tapatalk

author: penmarker
author_rank: Contributor
timestamp: September 21, 2017, 02:16:15 am
content: I looked through google to see what other laptop adapter looks like and I found a familiar looking board.So it turns out my laptop adapter is just a generic OEM but I don't even have the intake choke. They must have cheaped out on the manufacturing.The link is to Alibaba listing.https://www.alibaba.com/product-detail/Alibaba-express-laptop-keyboard-to-usb_60285608444.htmlDoes this laptop board look safer? Is the distance between the primary and secondary adequate? The board is similar to mine with exception of different component choices. Mine however has a lot of goop glue everywhere.

author: Rasz
author_rank: Super Contributor
timestamp: September 21, 2017, 02:44:22 pm
content: NEVER EVER buy "generic" chinese death trap laptop chargers.Its not only safer, but cheaper to source second hand brand name charger locally thru classifieds/olx/craigslist/gumtree/whatever from someone upgrading his laptop/selling off broken one.

author: b_force
author_rank: Super Contributor
timestamp: September 21, 2017, 02:58:52 pm
content: Or otherwise get a adapter/power supply from Meanwell.Very decent brand for these type of power supplies.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 21, 2017, 04:34:48 pm
content: Quote from: Rasz on September 21, 2017, 02:44:22 pmRight, and +1Envoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk

author: Gyro
author_rank: Super Contributor
timestamp: September 21, 2017, 04:43:28 pm
content: Quote from: penmarker on September 21, 2017, 02:16:15 amSimilar looking at first glance, until you check the track layout details. Do you see on yours (3rd photo in your OP) there are a couple of narrow feedback tracks that run above the transformer and gloop and straight into the secondary side on the right. I can't see any isolation [Edit: clearance] there at all.Now compare the underside of the one you just found. The feedback tracks run below the transformer to the secondary side (on the left this time). They stop at an opto isolator with the PCB underneath it slotted to increase creepage distance. They've even run a ground track around the secondary pins of the opto. Very 'belt and braces'. Good clearances between the primary and secondary sides in general.The devil really is in the detail even on apparently similar looking boards. Is that enough to say it's safe? Not really. I can't see the details of how well the Aluminium sheet primary and secondary heatsinks are insulated from PCB components on the other side (though the primary side one stops at the right place (next to the opto). I can't see the internal construction of the transformer windings and their insulation.All I can say from those photos is that the PCB was actually designed by someone with a brain in their head - a promising sign, but he may still have been let down by his purchasing department, assemblers and test department. Only evidence of test and approvals gives you that confirmation of safety.

author: penmarker
author_rank: Contributor
timestamp: September 22, 2017, 04:05:28 am
content: Thank you all for your replies.I've fitted the new input 150uF cap today but sadly it still won't work. I suspect the two mosfets are out.Don't think they'll last long anyway looking at the components. If there's anything genuine in there then I'm a monkey's uncle.Found replacement mosfets (MBR20100CT and STF10N65K3) but I don't think repairing it is worth any more of my time.Poubelle!Quote from: Gyro on September 21, 2017, 04:43:28 pmYou're right, they only look identical but the traces are different.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 22, 2017, 11:20:53 am
content: Quote from: penmarker on September 22, 2017, 04:05:28 amThe mosfets don't die of ageyou have also bad capacitors or bad flyback transformer or bad loop control like some IC not working... So for sure some time to spend... And start with current limiting for mosfet like some load in series with drain and watch on scope or if voltage get stable on output. Regards pierreEnvoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk