Postmortem Analysis of Dead Sonoff TH16 Wireless Switch | Hacker News Reader

Postmortem Analysis of Dead Sonoff TH16 Wireless Switch

cnx-software.com

69 pointswatchdogtimer31 comments

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).

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?

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.

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...

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.

Likely very slowly

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.

Sometimes ants gets attracted to some specific electronic equipment.

http://www.johnnywander.com/comic/aaaaaaaaaaaa

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...

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...

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.

I bought 6 or so and none of them looked like that, they were all spotless. I know because I opened them all up to flash them.

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

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

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

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.

> moths

I think I spotted your problem with bugs.

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!

Buggy hardware will get you every time!

So its a bug?

GDPR blocked, not going to read it.

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.

I'm using QuantCast Choice Wordpress plugin.

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 AntVoice.

This should be a thing like tl;dr

eu;cr

Or just a mirror of pages (like archive.is?) that don't do any user tracking, so no GDPR "wall" required.

Only if you have JavaScript enabled apparently. Works for me.

You don't need to disable JS entirely; disabling JS by default from third party origins (i.e. uMatrix) is entirely sufficient to block almost all of these things.

Seems that happens only once, but you can go back and are not nagged again. So he doesn't bare you from reading it, just takes the opportunity to explain why he is not happy with our decision.

You can just click back and it lets you read. I don't like the redirect, but nothing is being blocked.

I guess VPN providers are the only ones who applaud the GDPR ;-)

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.

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