Sonoff S31 failure repair

[tsmoneta]

In case anyone runs into this:

I have 55 Sonoff S31 running Tasmota. Recently one failed (would no longer connect to WiFi, made a slight buzzing noise), so I put it aside to check out later. A few days later, a second one did the same. I realized that the two came from the same order, because they were sequentially named (s31plug32 and s31plug33).

Disassembling, I found that a capacitor was slightly rounded on top, and it had pooped.

I cut the capacitor in half with a diagonal cut plier, and pulled the lower portion of the capacitor off, exposing the contacts.

After cleaning the goop off the board with an alcohol prep pad, I replaced the capacitor with a 16V 330μF capacitor I had in the house. Reassembled and it came immediately online. Repeated the operation on the second failure, and it also worked.

I figure Sonoff ran onto a bad batch of capacitors (reminiscent of the capacitor plague.

[Wintespe]

The electrolytic capacitor may function for a short time. Since the capacitance is lower, the voltage ripple increases. This results in an increase of the current load and thus the operating temperature of the electrolytic capacitors. This shortens the life time. A capacitor with low ESR (less than 100 milliohms) should also be used, otherwise there will be more ripple..

[sfromis]

Yeah, old capacitors are not exactly rare in cases of device failure. Earlier this year, I replaced a similar capacitor on a old Sonoff S20.

[phildabill]

Can confirm it seems the capacitors used are probably of poor quality. Had 2 failures with the same cause this year. Also had a TP-Link Kasa HS200 crap out. Different brand capacitor but exact same specs.

Ordered some Rubycons off Digikey to replace them.