
Postmortem Analysis of Dead Sonoff TH16 Wireless Switch - watchdogtimer
https://www.cnx-software.com/2018/05/30/sonoff-th16-wireless-switch-dead-postmortem-analysis/
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avian
It happens I'm a bit familiar with this circuit. I think the author misread
the schematic. The burned-out component is more likely the current-sense
resistor R2 (4.64 ohms).

In any case, it's unlikely that a 1.5 Mohm resistor would burn out like that.
Ant or not, you would need a lot higher than line voltage to cause that much
power dissipation over 1.5 Mohm.

The combination of two series 1.5 Mohm resistors R3 and R4 is actually well
visible in the first photo (two undamaged components with "155" printed on
them).

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unwind
That's a great find, but given your experience with the circuit, and the
different diagnosis, how does that change the likely cause of the problem? Why
did the sense resistor get toasty?

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megous
You don't need all that much power to toast such a small resistor. Looks like
0805 package, which would be rated for 0.125W max. Easy to burn.

It probably burned because of something causing higher current draw than
expected by designers. Short or whatvever. If it failed open, which would be
expected, it might have acted as a fuse.

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pi-rat
Reminds me of a LAN party with friends back in the early 90s, one of our
computers suddenly shut down while playing Doom, and would not power back up.

We opened up the case to check for any obvious problems, like a loose
connector or similar. On the motherboard, next to all the capacitors and
inductors near the CPU sat a fried garden slug...

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fhood
For real though, how on earth did a slug get into a computer case. I don't
think I have ever found a slug indoors.

~~~
mrguyorama
Likely very slowly

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TwiztidK
A few years back my company installed a few thousand capacitor bank
controllers on the bottom utility poles. Sometime last summer, we started
doing routine inspections and found a few of them covered with ants. Turns out
that something in the door seal is really attractive to ants, which seems like
something to avoid in a product typically installed outdoors.

~~~
kens
I had a nest of ants move into my driveway gate controller, eggs and all:
[http://www.righto.com/2010/08/getting-literal-bugs-out-of-
dr...](http://www.righto.com/2010/08/getting-literal-bugs-out-of-
driveway.html)

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rmoriz
Yesterday I was getting 4 new Sonoff Basic switches (2 from Gearbest, 2 from
Rosegal). 2 of them were broken and looked somehow botched. Pictures (+blog
post in German, sorry) [https://blog.rolandmoriz.de/2018/05/30/warnung-vor-
sonoff-ba...](https://blog.rolandmoriz.de/2018/05/30/warnung-vor-sonoff-basic-
wireless-switches/)

While I was impressed by the Sonoff S20 build quality, at least the Sonoff
basic series seem to be unreliable and even dangerous to use.

~~~
kiallmacinnes
None of mine look like this.. Could you have bought fakes?

~~~
Rjevski
Would there be any profit in making fakes for those, given the already very
low price of the original?

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kiallmacinnes
I'd say so! They are cheap from Sonoff, but way cheaper knockoffs are
available on AliExpress.

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StapleHorse
I never had this problem with bugs :)

I have two dead sonoff and I was expecting a more applicable postmortem
analysis. In my case looks like a failure of the integrated power supply in
both cases as I can power and flash the ES8266 from the TX,RX,VCC,GND pins.

They worked for moths and still have some others running strong.

~~~
jacquesm
> moths

I think I spotted your problem with bugs.

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buserror
Or, "ants like flux residue!"! Rosin based, aka resin based, aka probably
yummy smelling for an ant!

I was half expecting an article on how the hardware was badly designed, but
apparently, it's rather conservative in the ratings they used -- that is,
until a little mobile short moves in!

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elcritch
Buggy hardware will get you every time!

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CptMauli
So its a bug?

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physicsguy
GDPR blocked, not going to read it.

~~~
douglasfshearer
What is the GDPR acceptance interface being used here? I am assuming it is a
plugin or third-party service, since Macrumors have an identical one.

~~~
cnxsoft
I'm using QuantCast Choice Wordpress plugin.

~~~
Rjevski
Just wondering, why don’t you disable all of that tracking? I just checked the
opt-out screen and there’s literally _hundreds_ of ad “partners” (partners in
crime that is).

Ironically, one of those “partners” is called _Ant_ Voice.

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t3trinetet
I had an electrical timer that actually stopped not of electrical issues
caused by bugs but simply because it was so completely filled with earwigs
that it stopped turning. I guess the few extra degrees or something was enough
to attract them.

