Automatic Opening Kitchen Bin Repair

Some time ago I bought an “Automatic Opening Kitchen Bin” from Amazon.

I would provide a link, but I don’t think they stock the particular one I bought, probably because it is unreliable. The idea is that you wave your hand over the top of the bin and it magically opens. It then closes a few seconds later. Mine doesn’t.

Turning the top over, you can see it is secured with 10 screws.

These come out easily with a number one Phillips screwdriver.

At the back, there is a motor, battery box and on-off switch.

At the front there is the sensor, brains and motor driver board.

From the video at the start of this post, you can see that the sensor works. It does try to open the bin. It doesn’t fully open it, it kinda does an open/close movement.

The bin is then held slightly open for a reasonable amount of time, then it closes in a satisfyingly purposeful manner.

So, to summarise…

  1. The sensor works fine.
  2. The open function doesn’t work well at all.
  3. The timer works fine.
  4. The close function works perfectly.

So my bet is that the motor driver part is faulty. Let’s have a closer look at that board.

Wow! I was not expecting such a complex board for such a simple job.

You can see the IC in the centre of the board, I guess that is some sort of microcontroller handling the timing and sending open/close signals.

You can see the four transistors on the left hand side of the board. My guess is that these are forming a H-Bridge motor driver circuit.

They are labelled

  1. Q2 – SS8550 flat face to the right.
  2. Q3 – SS0850 flat face to the left.
  3. Q4 – SS8550 flat face to the right
  4. Q5 – SS8050 flat face to the left.

SS8550 is a PNP transistor

SS8050 is it’s NPN sister.

There is a description of an H-Bridge on “Learning about electronics” It is helpful. Given that I’ve found 4 transistors of the correct types to form a H-Bridge, I’m going to stop my investigations there and just make the wild assumption that one of these has died. I’ll replace them all and see if it works afterwards.

I pulled out the transitors (using my fabulous desoldering “moo” gun) and tested them. All but one tested OK, but one SS8050 showed…

Which doesn’t look at all “transistory” I think it (and it’s sisters) need replacing. Fortunately I’ve just bought a big box of transistors.

So I installed new replacements, put everything back together and gave it a quick test.

No difference, still the same slow open and half close.

Maybe it’s the motor. The wiring round there is a bit of a mess, there is a rather hacked together mess around an opto pair with a flag wheel. I pulled the motor out and checked how it engaged with the arm that opens the bin lid. All looked clean, well lubricated and no signs of wear.

Then I did the most obvious thing – the thing I should have done first… I changed the batteries.

Lesson learned. Check the basics first.

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