EEVblog #330 – Medela Swing Teardown & RepairPosted on August 8th, 2012 9 comments
Teardown, troubleshooting, and repair of a Medela Swing Breast Pump.
Great stuff! Awesome… Ordering my Rigol next week hopefully, Have already replaced the old meter with 2 fluke 177s 1 new, 1 used. Waiting on Hakko you suggested in one of your videos. Still have a lot left to buy, but you’ve put me on the right track as to what I need. Thanx for the great info. Ive always been facinated with electronics, working with many amazing things every day in my industry. Biomedical. Computed tomography (CT scans) X-ray machines, Dental chairs, Electric hand pieces, just about anything you can imagine, Lasers even. All dental related. Being a tinkerer at heart since I was a child Ive always been trying to make things better. Im looking forward to my transition from ordering new boards, and replacing equipment to repairing existing. In my industry I come across a lot of equipment that parts are not available any longer. I want to be able to help my customers by giving them a choice. You can buy new if you want to upgrade. Or i can repair what you have. It can be a difference of 10.00 dollars or so in electronic components vs. 100,000 thousand or so to replace Item. Im always striving to be the best I can be, and to always be able to offer my customers the absolute best.
The problem with just the series diode is that you have constant power dissipation during operation whereas having the parallel reverse biased diode you only have the leakage current causeing loss.
There are plenty of ways to implement reverse battery protection with less forward drop and dissipation than a simple series diode (good subject for an EEVBlog tutorial maybe?)
Just off the top of my head; resettable PTC fuse, MOSFET with sense, and plenty of proprietary little chip solutions out there. A large contact relay can have very low drop and dissipation, but it the slowest to act.
Heck, if you pick your regulator part properly it will come with efficient reverse protection already built-in!
If your circuitry is so sensitive it cannot even withstand reverse voltage for the short time it takes electronic protection to act, you can also add the diode across the supply rail. The diode will dissapate a lot when the reverse voltage is applied, thereby protecting the circuit. But not for long enough to harm the diode. This requires careful design however.
Here’s a video on using a PFET for reverse protection…
There are only a few explanations that come to mind quickly for the poor way the brute reverse battery crowbar protection was designed in this pump:
1. Plain old bad design.
2. The mechanical battery holders were supposed to prevent the user from ever installing the batteries backwards – and didn’t. (Or Dave was mucking around in there before and shorted something, he-he).
3. Planned failure (Evil Marketing).
Regards, David in Jakarta
As clever as the molding of the housing parts are, the molded markings are no match for some colored paint or a label to indicate battery polarity.
…And that little fuse would send the whole lot to the bin. Yet most people with even a cursory knowledge of electronics would check that fuse upon seeing it, find it blown and be able to bodge a replacement.
it´s always a great pleasure to see your videos. Thanks a lot for being a real fantastic mentor to me!
It took me quite a long time to realize what´s a “breast pump” (first thought its a medical surviving gear) but as I finally got it, it was clear to me what´s the sense of the second output on your scope (not the motor one). I´m quite sure its controlling an air valve and it´s the “gentle releasing function”, the opposite of the motor suction.
So the motor creates a vacuum for getting the milk out of the breast, and for sure this vacuum then has to be relesed in a fine way not to hurt “mamas tits”.
Does that make sense?
Best regards from Germany,
Isn’t it possible that the sensor signal is the output of a vacuum sensor? It’d make sense I guess: the MCU controlling the motor according to the actual vacuum level (and operation parameters).
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