[nSLUG] [OT] Re: Any electronic hardware wizards here?

Mike Spencer mspencer at tallships.ca
Fri Nov 7 01:34:45 AST 2008


Dop> I would expect it to be essentially an array of resistors
Dop> embedded in the blanket, and the connectors are fraying or
Dop> flexing and coming loose or snapping. I would agree with the
Dop> gurus that this is really not worth repairing, but if you want to
Dop> try it on a dead blanket, tear the blanket apart...

Did that once years ago.  There were little vinyl-encapsulated
mechanical thermostats in the blanket. No longer. Dead tech. The
"wires" are non-conductive fibre flat-wound (like a flat-wound guitar
string) with a fine conductive strip, making them reasonably resistant
to fatigue-hardening and fracture.

Dop> My personal recommendation would be a couple of hot water bottles
Dop> and extra layers of blankets/duvets/etc. This works fine for me
Dop> with the thermostat set to 10C.

My bedroom is unheated, ergo as low as, say, -17C.  Alternative in
mid-winter is an arctic mummy bag. :-\

Gerald> Can you be more specific about what stopped working? Does some
Gerald> of it get warm? Do some settings on the control work?

   + Controls appear to work: LC display shows (putative) settings;
     shows "PH" when pre-heat is pressed, shows error code if blanket
     is not connected.

   + Nothing gets warm.

   + External connections are all tight.

   + Sewn-in plug/connector appears (superficially) to be okay.

Dan> Funny, I was just thinking the other day how weird it was that
Dan> the "double" bed size dual control electric blanket that I bought
Dan> a quarter century ago was still working fine, and I've used every
Dan> night, every winter since then.

Priceless, old stuff. Now that the chief valued assets of corporations
are brands, the actual, tangible products are becoming cargo-cult
simulacra.  Blacksmiths have an acronym -- ASO -- for those things from
Harbor Freight or Princess Auto: Anvil Shaped Object.

Dan> ...but the wires somewhere in the blanket, of the classic flexed
Dan> "wire disease," probably where they join the three-prong
Dan> connector at the foot of the blanket.

I fixed one like that once. Unstitched the blanket, cut away the
plastic plug to expose the embedded wire, re-attached the blanket
wire, re-embedded it in silicone goo.  I guess that's the next thing
to look at.  But other folks out there on the net also complain of
gradual failure.

Dan> The control is pure mechanical bimetallic spring with its own tiny  
Dan> heater...

But not on new ones. More dead tech, more's the pity.

Dan> So - starting from basics: you're sure it's the control that has
Dan> failed?

No. Having cut one open with a tiny circular saw on a dental drill, I
can't see anything that is likely to have failed in there. No leaking
cap or visibly fried component. Has an IC chip, misc. tiny components,
a cap and what I take to be a (power?) transistor -- black rectangle
with three comparatively hefty legs and a aluminum heat sink/radiator.

Dan> In a sense - the "resistor" is the wire itself -- a helix of a
Dan> fine copper filament...

In the last one I dismembered, the wire didn't look like copper and
didn't solder worth doodly-squat.  But the wire is apparently the
resistor. If there are discrete resistors or sensors in the blanket, I
haven't spotted them.

Dan> ... wrapped around some fiber, all embedded in vinyl.   

Yeah.

Dan> You'll feel numerous bumps in the blanket itself;...

Not any more.

Dan> ...these are overtemperature fusible links which keep it from
Dan> overheating

Were.  I don't know how present tech senses local overheating.

Thanks, all, for the non-hostile replies to a grossly OT query.
Feel free to continue off-list if you're actually interested in the
subject and might help with my (obsessive?) attitude toward
intentionally unrepairable cargo-cult consumer appliances.


- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^



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