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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: Suspension losses
Date: Sun, 12 Jan 2025 21:11:37 -0500
Organization: A noiseless patient Spider
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On 1/12/2025 5:13 PM, Jeff Liebermann wrote:
> On Fri, 10 Jan 2025 20:01:26 -0500, Frank Krygowski
> <frkrygow@sbcglobal.net> wrote:
> 
>> Two days ago, my kid asked me to figure out why an electric blanket
>> wasn't working. The controller refused to turn on. I opened it and
>> confirmed that it was getting supply voltage. Beyond that, the pile of
>> dozens of surface mount electronic components was incomprehensible to
>> me. I suspect Jeff might have been able to diagnose it, but not me.
>> Here's a photo:
>> https://www.flickr.com/photos/16972296@N08/54259119364/in/dateposted-public/
> 
> I don't think I can do much with just a photograph.  If you have the
> maker, model and FCC ID number, I can do better.  Also, some
> indication of what it does when the power is applied, such as do the
> LED's light.  If the don't light, try again in the dark and see if
> they partially light.

There was no action at all, no lights, nothing.

> Looking at the PCB components, I would guess it's 2000 to 2010
> vintage.  In other words, it's old.  I can't read any of the part
> numbers from the photo.  If the SOT-24 package (probably a PIC
> Microcontroller) has a date, that would determine the age.  Looking at
> an enlargement of the photo, I notice that some of the components
> (LED's and pushbutton switches) were hand soldered.  Enlarging the
> photo showed several possible places where the soldering looks like a
> volcano with a black annular ring around the center component lead.
> That's about all I can do with just a photo.

I thought about bad solder joints and looked pretty carefully, but 
didn't see any that looked suspicious. I didn't go so far as to follow 
the traces to see where voltage went away. The owner is quite prosperous 
and lives a distance away, and was saying "Dinner is ready!" She'll just 
buy a new one. I figure I did my duty by eliminating obvious faults and 
by pointing out that the blanket itself was still good, so just replace 
the controller.

>> I know electric blankets are old technology. I know they functioned well
>> for decades with maybe a rheostat and perhaps a couple of other
>> components. Why add unrepairable complexity?
> 
> I don't want to write a lengthy essay on topic.  Your rheostat
> probably was fine for mid 20th century technology, but would never
> pass the safety standards that followed.  Those safety standards were
> there for a good reason such as killing the customer by fire or
> electrocution. 

Yes, I surmised that was the motivation. The terrible plague of electric 
blanket deaths has finally been conquered! We are safer every year!

- Frank Krygowski