Since I’ve been documenting failure modes in electronics, another tale of electronic woe regarding N109 type knockoff Lenovo 90W AC adapters. I have a couple T series ThinkPads, which conveniently all use the same 20V 90W supplies with the same connector. I noticed that the stress relief on one of my AC adapters was wearing, so, having had a streak of good luck buying various direct-from-China products, I bought a knockoff replacement adapter that way.
I would suggest that you don’t want do that.
It was fine for a couple weeks (sadly, long enough to give it indelible positive feedback at the vendor).
Then the case partially melted.
I blamed it on kicking a blanket over it while drawing power and didn’t worry much, figuring it was just cheaper plastics.
I was wrong.
Yesterday, while sitting with good ventilation on a desk, it cooked one of its caps off (for the uninitiated, electrolytic capacitors make a very distinctive smell and noise when they fail, and are among the most common failure modes for consumer electronics). Distressingly, it was still trying to supply power until I unplugged it.
Being me, I pulled it apart as soon as it cooled down enough to handle.
The heat deformation is centered behind what appears to be a 5N60C type N-Chanel MOSFET, although there is something that looks like a rectifier right next to it that I can’t read the label on around the also slightly melted 100µF 400V capacitor.
One of the pair of 680µF 25V capacitors on the output side was the source of the explosion. The label says it was only rated to 105°C, which I’m pretty sure was being exceeded whenever it was under load.
Also charming: note the indicator LED inside the solid black case. Clearly this circuit was custom designed for the application, and not just tossed in on the basis of being close enough.
I wish I’d thought to hook this thing up to an oscilloscope when I got it, looking at the circuit I suspect it has been emitting ripply garbage into my laptop the whole time. Hopefully it didn’t do any damage to the computer. One of these days I’ll say that enough times to give in and pick up a scope, the Rigol DS1102D scope + logic analyzers are getting ever more tempting.
Now, I’ll be getting rid of the husk so it stops stinking up my apartment. It looks like there are some possibly-authentic ones from reasonably reputable vendors for like $16-20 that are more likely to be worth owning.
