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About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Electronic Mixer Control Repair: Doing My Part to Reduce E-Waste

Braun kitchen hand mixer case opened - RF CafeJust because I don't wear Earth Day or 'Save the Whales' T-shirts or donate to their causes does not mean that I abide wanton and senseless destruction of our planet's resources and natural beauty. Do a search of RF Cafe and you will find many examples of articles I have written and headlines posted regarding offenders and, equally as important, the hypocrisy of many people and groups who are in your face constantly about these issues. Most of those types are either woefully stupid about and ignorant of how their actions are hypocritical, or are in it for the money and/or notoriety and don't care about their hypocrisy. The former join protests in opposition of petroleum companies while wearing clothes and owning devices manufactured in part from petroleum products, or made in factories whose machinery incorporated such materials. They conveniently ignore the petroleum products consumed in transporting themselves and their consumables from point A to point B. The latter, like a particular former VP, make multiple millions of dollars demonizing petroleum while gluttonously consuming it themselves.

Broken transistor lead on Braun hand mixer - RF CafeMy approach is to be personally aware of and responsible for causing as little damage to the environment as possible while availing myself of a reasonable amount of modern conveniences. One way I do that is to repair, renovate, and repurpose many things ranging from houses to appliances. Melanie and I have renovated no fewer than half a dozen houses (while living in them) in the last 30 years. We have not purchased a lot of excess stuff over time, and nearly always donate things we don't need anymore rather than sell or throw it away. I feel no guilt.

My latest example of repair is a Braun kitchen hand mixer that we've had for at least two decades. The blue heat shrink tubing on the power cord was part of a repair done many years ago. Recently, Melanie reported that the multi-speed switch seemed to be intermittent. After confirming the symptom, I opened the case and removed the switch assembly. Fortunately, it was held together with locking tabs rather than glue. I popped it open and found some of the contacts to be pitted and covered with arcing residue. I reconditioned the contacts, cleaned everything, and snapped the switch case back together. So confident was I of the repair that I even reassembled the entire mixer. I plugged it in and now it didn't work at all! A major deflation of ego accompanied the failure.

Thereupon, I took it apart again and verified the switch positions with a multimeter. Everything was AOK. In the process, I noticed that one of the motor control transistor leads was broken (see lower photo). It doesn't get much more obvious than that. Fortunately, the portion of the lead soldered to the PCB had a lot of extra length so it was possible to heat the joint and pull enough through to mate sufficiently with the part of the lead on the transistor package. A little emery cloth, a little flux, a little heat, and a little solder (PbSn -- OMG, I am an eco terrorist after all!) did the trick. Daunted by my aforementioned failing of technical prowess, this time I plugged the mixer in and tested it prior to putting everything back together. It worked perfectly.

My guess is that over time, this heavily used mixer was banged around enough to cause a fatigue failure in the lead, no doubt assisted by the fact that the heat sink is not supported, adding an extra measure of force to the transistor frame with each impact. I am somewhat ashamed to admit that I did not take advantage of the opportunity to properly secure it. I'll do it next time.

Interestingly, about 10 years ago Melanie's big countertop Mixmaster (Sunbeam) stopped working. The motor control transistor had fried on it, and at the time I was actually able to buy a replacement at the local Radio Shack. I doubt they even stock such a selection of devices anymore, although there is still a lot available online. In fact, very recently I bought a couple 10 W wirewound resistors from Radio Shack online; they had the best price for what I needed.

 

 

 

 

Posted on  April 29, 2015

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