In this Instructable, I will be showing you how I repaired my brother's Mi Air Purifier Pro that went bang while working.

The purifier was just about one year old and just a few weeks after the warranty period was over so I wanted to see if I can repair it myself, instead of taking it to a repair shop.

As a warning, please note that this device operates on mains voltage and you need to be extra careful when dealing with it. Mains voltage can easily hurt you or even kill you!

Supplies

Tools and materials used in the video:

ACM3-CA-PWXR Mi Air Purifier Pro Power Module - https://s.click.aliexpress.com/e/_AphZTt
JCD 8898 Soldering Station - https://s.click.aliexpress.com/e/_9z7oVp
Screwdriver Set - https://s.click.aliexpress.com/e/_AONVML
Multimeter - https://s.click.aliexpress.com/e/_9xHSYP
Desoldering pump - https://s.click.aliexpress.com/e/_A8zEdZ

Step 1: Remove the Filter

With no obvious screws, the first thing that I did was to remove the filter through the door on the back.

Step 2: Open Bottom Cover

With the filter removed. I flipped the purifier upside down so I can access the bottom cover.

Here under the 4 rubber feet, there are screws that hold it in place.

Keep in mind that one of these screws has a sticker attached and that sticker will get damaged when removed. If your purifier is still under warranty, do not open it as that will void it.

Step 3: Inspect the Power Module

Under the bottom cover, there is a power module that converts the 230V from the mains down to 24V for the purifier.

Immediately after I removed the cover, I noticed that there are signs of liquid on it, and at first, I thought that something must have been poured into it from the top.

However, after some further inspection, I saw that the main electrolytic capacitor on the board have bulged and the liquid signs were from its electrolyte.

It's possible that this electrolyte might have caused a short or since the capacitor was damaged, the rest of the circuit was pushed to its limit and it had to fail.

It is quite possible that the original board is repairable, but I managed to source a replacement online and i decided to replace it completely, just to be on the safe side.

Step 4: Switch Connector and Fix Broken Capacitor

When the replacement board arrived, it was obvious that it had a rough journey and it experienced damage to its main capacitor.

Luckily, the capacitor was only removed from the solder joins and I was able to solder it back in place.

When I ordered the board, I saw that the replacement had a different connector than the original, so I also switched the power connectors between the boards.

Step 5: Test Replacement Module

Since the replacement board got damaged in shipping, I wanted to confirm that after the repair, it worked as expected so I plugged it in on my bench to measure the output voltage.

If you do the same be aware that the board is powered from the mains and that there is main voltage exposed so be extra careful when handling the board.

With the multimeter, I measured the output and it showed the expected 24V so I knew that the board is OK to be replaced.

BUT, before handling this board to reinsert it into the purifier, make sure to give it enough time to discharge its power capacitor as it can contain a lot of power in it. When I measured the capacitor it was charged to around 300V and that can give you quite a serious zapp if you touch it.

To make sure that I don't get zapped, I used my pliers to short out the capacitor and that produced some really big sparks.

Step 6: Reassemble and Test

The module can be reinstalled by placing it in the tray and securing all of the screws.

Once everything is back in place, I turned on the purifier and I was greeted by the Mi logo on the screen.

When I power on the air purifier, it started operating normally so I knew that I could call this repair a success!

If you liked this repair, then be sure to check out my website, my other Instructables as well as my YouTube channel where you will find a lot more repairs and projects similar to this one.