Re: Suspension losses

On Sun, 12 Jan 2025 21:11:37 -0500, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:

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.

That makes troubleshooting easy.  There has to be a fuse or thermal
circuit breaker in there somewhere.  I can't see one on the PCB
(printed circuit board).  It's a single sided PCB so it's unlikely
that it's hiding on the back of the PCB.  It's either inside the wall
plug, inside some kind of on/off switch box that's in series with the
power cord, or attached to the blanket somewhere.

I took a 2nd look at the PCB and found some more things that look
suspicious.
<https://www.learnbydestroying.com/jeffl/crud/electric-blanket-control.jpg>
It's a single sided (nothing but the cheapest) PCB.  That means that
any wires going through the pads on the PCB need to be well soldered
or they will literally fall off.  I circled 6 solder connections that
don't look quite right.  (Oops.  I missed one).  Compare these solder
connections with the ones that look good on the left side of the PCB.

There are also 4 connection on the upper left with don't look right.
What is the black stuff on the leads?  Melted plastic?  The labels S1
S2 are wires to a switch.  H1 and H2 are heater wires.

If you want me to continue, please provide the maker, model number,
and FCC ID if available.

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.

After I look for suspicious cold solder connections, I just resolder
the connections.

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.

We have a different view of the problem.  I look my duty is to prevent
yet another piece of almost working electronics from ending up in the
recycling bin.

"Recycling Isn’t the Answer; It’s the Last Resort"
<https://www.ifixit.com/Right-to-Repair/Recycling>

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

Thank you for the cynical comment of the day. 

"Electric Blanket Fire Lawyer"
<https://www.killinofirm.com/practice-areas/electric-blanket-fire-lawyer>
"Electric blankets cause about 5,000 house fires per year in the US,
resulting in dozens of injuries and even death."


--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558