P.O.S. Chinese SMPS killed my laptop!! - Page 1
Forum section: electronics / projects

author: CaptDon
author_rank: Super Contributor
timestamp: February 25, 2024, 10:08:27 pm
content: Should have been more careful, should have known!! 19VDC SMPS with '2-prong' line cord and no ground. Had my laptop powered up and when I plugged the audio cable from my grounded (a.c. cord with three prongs) guitar amplifier into the laptop KA-BOOM....smoke rolls out of the laptop!Looks like the .33uf cap from the A.C. line inside the SMPS failed dead short!! I must have been shit lucky in the past to have plugged the non-polarized 2 prong line cord into the outlet in such a way as the .33 cap was on the neutral side and didn't cause a problem? I have used this setup before with no smoke but today cost me a laptop!! Motherboard was blown big time. Old dinosaur guitar amp still works perfect! The 1/4" input jack is chassis grounded steel to steel and the chassis is grounded via line cord. Laptop became the fuse!!! I did get some satisfaction beating the shit out of the power supply with a hammer!! Kind of strange the 2 prong power cord wasn't polarized? May not have mattered?

author: amyk
author_rank: Super Contributor
timestamp: February 25, 2024, 10:15:35 pm
content: Likely a non-safety rated Y capacitor that failed short.

author: floobydust
author_rank: Super Contributor
timestamp: February 25, 2024, 10:18:55 pm
content: After seeing Big Clive's adapter fail teardown, where it shorted mains HV DC bus to output(-) due to the hazardous live heatsink shorting to the output inductor, very scary, fuse was bypassed. No hi-pot test, fake safety approvals.OP a 0.33uF film cap is X-cap and should not kill the laptop. Wonder what this cap is that failed short. Y-cap is typ. 2,200pF ceramic.Why do people pay and power expensive stuff worth $1,000's dollars from cheap chinese unsafe power supplies?

author: ejeffrey
author_rank: Super Contributor
timestamp: February 26, 2024, 12:39:52 am
content: Quote from: CaptDon on February 25, 2024, 10:08:27 pmNot much reason for an ungrounded, "double insulated" power brick to be polarized. There is not even any obvious way to choose which side should be neutral.

author: Gyro
author_rank: Super Contributor
timestamp: February 26, 2024, 10:10:42 am
content: Without seeing photos of the OP's SMPS (which would be very interesting). I suspect that the primary - secondary capacitor is actually after the bridge rectifier and so, plug insertion direction independent. With an improperly rated or fake Y cap (I don't understand the 0.33uF, more likely would be a 3300pF), catastrophic failure is only a matter of time, and maybe a mains spike away!

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2024, 10:13:05 am
content: You are very lucky it killed the laptop and not the user.If from Ebay, just learn not to buy any mains supplies there. If from a local importer, report to authorities ASAP, it's a high priority issue.

author: Miyuki
author_rank: Frequent Contributor
timestamp: February 26, 2024, 11:09:58 am
content: I have one funny SMPS (19V 4.74A) that was with a soldering station, it uses 3 pin mains cable, so I expected it to be grounded or at least reasonably insulated, but still builds a pretty big charge at the outputWhen the soldering iron touches something grounded a small spark comes out

author: CaptDon
author_rank: Super Contributor
timestamp: February 26, 2024, 01:57:50 pm
content: The cap that shorted was a gray rectangular thing and indeed marked .33uf, I don't recall the VAC marking but I assume it was 250vac which is typical. I didn't take time to see which side of the B.R. the cap was connected to. After the blow up I grabbed my meter and measured 120vac from the sleeve of the D.C. connector to house receptacle ground and also measured 0.1 ohms from sleeve of D.C. connector to one of the line cord prongs. Power brick is gone in the trash after taking out my frustration on it with a hammer causing 'user stress marks'. I only saved the line cord since it fits my DMX stage lighting devices. This power brick had some age on it, definitely chinese made. Perhaps it has been bad for a while since I had not connected that laptop to my sound system for a month or so. Hard lesson learned however!! I think I will use 3 prong power packs only in the future and verify proper grounding / voltages between input and output. Cheers mates!!

author: factory
author_rank: Super Contributor
timestamp: February 27, 2024, 11:13:42 am
content: If the line cord was supplied with it, then it might use the dangerous copper colored steeloraluminium wires inside, this is a fire hazard if there is a short circuit.David

author: Gyro
author_rank: Super Contributor
timestamp: February 27, 2024, 07:16:10 pm
content: Quote from: CaptDon on February 26, 2024, 01:57:50 pmCurious, that sounds like the X cap, which would have been across mains L-N, not primary-secondary. Something else must have shorted - transformer, opto, dodgy Y cap or compromised primary-secondary clearance somewhere on the board, heatsinks etc.