- Blog entry posted in 'Teardowns', May 09, 2013.
My tower fan stopped working, so i figured i should take a look at it. it was surpsing hard to open in the end, but was made possible, nothing broke up.
Repair itself: At first, nothing really showed up, no bulged caps or anything else sucpicious at first. I measured the voltage pins for transformer, and it turned up to be okay. Then, when i plugged it, somewhat bigger spark came from dc-socket. I measured supply voltage pins for controller chip, 5v as datasheet says, so at least it gets supply voltage. After that, i realized that couple of smd-transistor were pretty warm, hot actually, so i measured them just to make sure they are not SC/OC, they turned out to be just fine. But, then i felt AHA, when i saw possible fault. One of the caps leads were left too long, and it was bent over to wrong place, causing SC. No wonder there was spark at dc-socket. I snipped feet smaller, and 'voila, repair success. Also, i noticed couple bad solderings, which i repair too. Well, i guess made-in-china says it all, but why it worked before just fine?.
But, i took photos also, so here comes teardown:
Inside was 12v brushless fan, and some cind of synchronous 12v motor, for pendulum movement. Pushbuttons for speed adjustment at 3 steps, pendulum on/off, and main power.
The ''brains'' are HT46R47 battery charger controller. Funny, this is fan, not a battery charger, but as it turned out, this controller has PWM output, so nothing strange there after all :D. I played around a bit when i was measuring the output waveform of PWM pin, and yes it indeed changed duty cycle as speed changed. I also stress-tested system too, by braking the fan, and controller responced by increasing duty cycle. Also, i found out that 1/10x at scope probe really matters, when i measured at x1 position, the was more noice, and fan shutted off. At x10, no problem.
