Sound familiar? Your Sonoff S20 smart plugs worked reliably for years, but suddenly they keep dropping their WiFi connection. A restart fixes things — for a few hours. Then the same thing happens all over again. You simply can’t build a reliable smart home on devices like that.
The good news: in most cases you can fix the problem yourself for under a dollar in parts. The secret lies in a tiny component that loses its electrical properties after a few years.
The Common Problem: Unstable WiFi Connection
Recognizing the Symptoms
The problem tends to show up in a very characteristic way:
- The Sonoff S20 sporadically drops its WiFi connection
- After a restart everything works again for minutes to hours
- The device stops responding to commands from the app
- The LED blinks irregularly or shows error states
The Root Cause: Capacitor Aging
What looks like a WiFi problem at first glance actually originates in the plug’s power supply. After some research it became clear: the electrolytic capacitors used in these devices lose their rated parameters after a few years.
This causes instability throughout the entire power supply circuit — instability that the ESP8266 microcontroller cannot handle. In the worst case the device eventually dies completely.
The $1 Repair: Step by Step
What You Need
- One 330µF/16V electrolytic capacitor
- A soldering iron and some solder
- A Phillips screwdriver
- Desoldering braid (helpful but optional)
- Common sense when it comes to safety
Important safety notice: Never work on the plug while it is connected to mains power!
Opening the Case
The Sonoff S20 is surprisingly easy to open. Remove four Phillips screws and you have access to the circuit board. The video shows you step by step exactly where the screws are located and how to open the case safely without damaging anything.
Identifying the Culprit
The problematic capacitors are easy to spot. They are the electrolytic capacitors in the power supply area of the board. The main suspect is the 330µF/16V capacitor located between two IC chips.
The tricky part: these capacitors look completely normal from the outside. No bulging, no visible damage — yet they are faulty. The video shows you exactly where to find the suspect capacitors and how to tell them apart from other components.
Removing the Faulty Capacitor
To replace the capacitor you need to partially loosen the board so you can reach the solder joints from the back. The relevant contacts sit between the two chips and need to be carefully desoldered.
The video shows the soldering iron work live, including tips for avoiding damage to the board. Clearing the holes after removing the old capacitor is covered in detail — that is the trickiest part of the whole repair.
Installing the New Capacitor
When inserting the new 330µF/16V electrolytic capacitor, polarity is critical:
- Negative lead: Marked with a thick stripe
- Positive lead: The other side (longer leg)
The board markings show you exactly which way the capacitor goes. Positive on top, negative on the bottom — following the markings on the board. The video demonstrates slowly and clearly how to identify the correct polarity and align the capacitor properly. Getting this wrong would destroy the entire power supply!
Reassembly
When reassembling, pay close attention to the correct positioning of the button. The small transparent plastic piece must sit precisely on its pins, otherwise the manual button will no longer work.
Also make sure the cables are routed so they do not conflict with the socket contacts. The video shows the small but important trick with the button — miss it and you will regret it later!
The Moment of Truth
After screwing everything back together comes the exciting part: the first power-up. If everything was done correctly, the LED starts blinking happily and the plug connects to the WiFi without any trouble.
The video shows the successful result live: the repaired Sonoff S20 is fully reachable at its IP address and switches flawlessly — something that was not possible before. That moment is genuinely satisfying and proves the effort was worth it.
Why the Repair Is Worth It
Sustainability Over Throwaway Culture
Instead of throwing away the “broken” plug and buying a new one, you invest about 30 minutes of time and under a dollar in parts. That is not only sustainable — it is also educational.
Other Affected Components
If replacing the first capacitor does not solve the problem, the other electrolytic capacitors in the circuit may also be affected. The repair principle stays the same.
Long-Term Stability
After the repair the plugs work perfectly again. The WiFi connection is stable, response times are fast, and reliability is back to its original level.
Practical Tips for the Future
Prevention
Electrolytic capacitors age due to heat and operating time. Avoid placing your Sonoff devices in excessively warm environments and ensure adequate ventilation.
When Is a Repair Worth It?
For devices older than 2–3 years that show the WiFi problems described above, a faulty capacitor is very likely the cause. The repair is usually successful and only takes a few minutes.
More Hardware Repair Projects Ahead
This repair shows impressively how sustainable smart home can be. Instead of discarding working hardware, we fix it with minimal effort. The best part: the video shows not just the repair itself but also the reasoning behind it — what to look for when diagnosing the fault and which pitfalls to avoid.
More Repair Guides
- Fixing BROKEN Shellys – The 30-Cent Repair That Actually Works! – The same capacitor principle applied to the Shelly 2.5: solving WiFi problems with a new capacitor
- Replace a Tablet Battery Yourself – Save Your Old Device in 20 Minutes! – When your old tablet needs to last hours instead of minutes as a smart home dashboard again
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― Joachim