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Winix Air Filter won't power on. Found broken diode in power supply?

mfrankSD

Feb 16, 2022
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Feb 16, 2022
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Hi all, i'm somewhat new to electronics so forgive any ignorance...

I have a high-end room air filter (https://www.winixamerica.com/product/xq/) that won't power on.

I started looking at the power supply unit to see what's going on. No burned smells, or visually obvious broken components.

After some research, I figured out this is a flyback power supply. I'm seeing 167V at the primary side of the transformer (apparently rectifying 120V main with a rectifier increases the DC output by 1.4X).

All the components between the wall outlet power and the primary side of the transformer seem OK. At first, I thought maybe the switching IC went bad. The label printed on the component seems to match this guy https://www.hkkzd.com/products/1_6812934/tny286pg which indicates switching frequency 125-140kHz. I looked at some youtube videos and it looks like you measure frequency by putting one probe on the primary side and one probe on the secondary side? This didn't make intuitive sense to me. However, I did measure 150kHz. Slightly out of spec, but maybe my switcher is slightly different than the one in the above link.

On the secondary side, I don't measure any output voltage. There's some capacitors rated for 16V so I should be expecting 16V on the secondary side of the transformer. I'm not super confident that I know where to put the probes on the secondary side. There's two pins coming out on the secondary side of the transformer, I assume this is the + and - of the secondary DC circuit that should give me 16V.

After the secondary transformer, there's a diode. It appears to fail the diode test on my DMM but in a weird way. I measure 0.0V drop across this diode with EITHER polarity of my probes! So the diode has shorted? It should give me O.L. on reverse polarity and some measureable voltage drop on the other polarity. Now, the question is, if this diode is done for, does that explain why I am not getting power on the secondary side? My intuition says that diode is absolutely required for creating DC current because otherwise the current out of the transformer is oscillating.

I've uploaded pictures of the power supply, and I've circled the broken diode in RED.

Any help would be super appreciated! Thanks.
 

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kellys_eye

Jun 25, 2010
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Assuming there's nothing wrong with your meter then the diode is dud. Just to be sure, lift one end from the board and test again. Should read around 0.3V forward, 'infinite' in reverse.
 

mfrankSD

Feb 16, 2022
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Feb 16, 2022
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Yes the diode is a dud. I was able to replace the diode today… but still no luck. I’m expecting 16V on the secondary side but I’m not measuring anything. Above 0.9 V. The device is still unresponsive.

do you think I should replace the capacitors too?

strangely, I’m now measuring the switching frequency at 250kHz!

when I probe the pins of the switcher itself, I got a spark on the board. Is this catastrophic?
 

kellys_eye

Jun 25, 2010
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when I probe the pins of the switcher itself, I got a spark on the board. Is this catastrophic?
Potentially (even quite likely). A normal measurement wouldn't cause a spark at all. If you shorted any adjacent pins (likely) then you may have destroyed a component.

Get the datasheet for the main switching device (I'm assuming it's an integrated switcher?) as this will provide a useful schematic on how the unit has been designed and you can fault trace using the approximated data i.e. expected voltages and waveforms at the various pins etc
 
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