Re: Suspension losses

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