I ordered a compact weather station for a local project I am working on with a friend, and when it arrived we could not get a single byte of data out of it. Completely dead. No response on any address, no sign of life at all. Since we had already committed to using it, sending it back and waiting weeks for a replacement was not an option, so I decided to open it up and find out what was actually wrong inside.
What This Weather Station Does
This is one of those all in one compact stations that packs a lot of sensors into a single housing. It measures temperature and humidity, wind speed and wind direction, atmospheric pressure, rainfall, and light intensity in lux. The wind measurement is the interesting part, because instead of spinning cups and a vane it uses ultrasonic transducers mounted between two plates. Sound is sent between the transducers and the tiny differences in travel time tell the unit how fast the air is moving and from which direction. On top there is a rain bucket that tips as water collects, and a couple of light sensors sit near the end of the housing.
Everything talks over RS485, which is a digital communication standard built for industrial use. It is nice because it runs long cable lengths without losing the signal and it lets you put many devices on the same pair of wires. On top of RS485 the station speaks Modbus, which is the actual message format. Each device on the bus gets its own address, and you ask a device for data by sending a command with that address on it. If nothing on the bus has that address, nothing answers.
Proving the Problem Is Not the Cable
The first suspect in any situation like this is the cable, because it is the cheapest thing to be wrong and the easiest to fix. The station came with its own cable, so we tested that cable with a different sensor that we knew worked, and it passed. We also tried the station with a known good cable from another sensor. Same result. Nothing. So the cable was ruled out early and the fault had to be inside the station itself.
Next I powered it up on the bench. This unit accepts anywhere from 9 to 24 volts, so I set my bench supply to 12 volts and connected it. And this is where the first real clue showed up. The current reading stayed at zero. Not low, not fluctuating, just nothing at all. Even with the communication wires disconnected, a healthy sensor should still pull some current just to run its own microcontroller and regulators. A device that draws no current is not running, and a device that is not running will never answer on the bus no matter how nicely you ask.
Scanning the Whole Modbus Bus
To be thorough I still wanted to confirm it from the software side. I connected the station to a generic RS485 to USB converter, which is a small dongle that plugs into a computer and gives you screw terminals for the A and B communication lines. The station's label tells you the color coding, so yellow goes to A and green goes to B. Once that was wired up I plugged the dongle into the computer.
For talking to these sensors I use a Python tool that I wrote myself. It opens the serial port on the converter, wraps my requests in the Modbus format the sensors expect, and decodes the replies back into readable values. I have several sensor types set up in it already, including temperature and humidity units, wind speed, wind direction, and this compact weather station.
When I ran the tool it first asked which COM port to use and correctly detected the USB to serial adapter on COM 3. Then it started walking through the Modbus address range, sending a ping to every possible address from 1 all the way up to 247. This is worth understanding if you work with these sensors, because out of the factory almost all of them arrive preset to address 1, and it is your job to give each one a unique address once you build out your network. The scan ran to the very end and found absolutely nothing. To confirm we were not chasing the wrong address, I checked the official documentation for the station and it clearly states that 01 is the default. Since nobody had ever plugged this unit in before us, that address should have answered. It did not, so it was time to take the thing apart.
Opening It Up
On the bottom of the housing there were a few screws to remove, plus two plastic screws that looked purely mechanical since they tie into the mounting post. Those came out first and the bottom section separated without much fight. Inside I could see the cables held in place with some glue, running all the way up through the body of the station.
To actually reach the compartment where the electronics live I had to separate a second section, and that one needed Allen keys and four more screws. Even with all four out it did not want to come apart. After a bit of careful brute force I found the reason. There is a sealant, something like a liquid glue applied before the housing is tightened down, sitting in the groove between the two sections. It had to be broken to get in. That is worth knowing before you start, because this is an outdoor device and that seal is what keeps water out. I made a mental note to put a proper seal back in that groove during reassembly.
Checking Continuity on the External Cable
With the PCB accessible, the first thing I wanted to verify was that the external cable actually reaches the board electrically. All the internal wires were tacked down with hot glue, so I applied a small amount of isopropyl alcohol to soften it and gently peeled the glue away from the wires so I could see the solder pads clearly.
Zooming in on the board there were several sets of wires. One bundle came down from the top section, so that would be the rain bucket and probably the light sensors. Another bundle had six wires in it, likely pressure and humidity. And then there was a set of four wires that came in from the front, which are the ones connected to the external cable that runs out of the station.
I put my meter into continuity mode and tested each of those four. Red is the positive supply, and I found it on the pad I expected, reading just under an ohm. Black checked out the same way. Yellow, which is RS485 A, was also connected, and so was the last one. I also probed between wires to look for shorts, and there were none. So every wire had continuity from the outside connector to the board, and nothing was shorted together. That pointed to a bigger problem somewhere on the PCB.
Trying to Get the Board Out
Before lifting the board I made sure to note the orientation. There is an arrow printed on it marking the north side for installation, and that matters a lot on this unit. The ultrasonic wind transducers have to sit in a specific rotation for the direction readings to mean anything, so if you put the board back rotated, your wind direction will be wrong forever. I lined up the arrow in my head so I could return it exactly the same way.
I got all the screws out and tried to gently pull the board free, but it would not come. The four wires going to the ultrasonic transducers are buried deeper inside the housing than I expected, and I was not willing to desolder everything just to peek at the back side of the PCB. From what I could see through the gap, there was one capacitor over on that side and not much else. There is also an unpopulated SIM card slot on the board and a row of headers along the edge, which suggests this same design gets used for a cellular version of the product.
Probing the Power Rails
Since I could not flip the board, I decided to power it up and probe around with the multimeter to see where the voltage actually goes. I traced 12 volts coming in from the external supply, through some diodes, and onto a capacitor where I measured a little over 4.6 volts, close enough to 5. So that stage is a regulator, and from there the 5 volt rail continues through a diode up to the port for the top section. Then there is a second regulator, and on the capacitor after that I measured a clean 3.3 volts. Both rails were also present on the other connectors around the board.
That was confusing. Power was arriving, both regulators were doing their job, and 5 volts and 3.3 volts were reaching everywhere they should. Nothing about that matched a dead device.
The Fault That Made No Sense
So I went back to continuity testing, this time following the PCB traces instead of the wires. I noticed that two of the incoming wires connect to a little transistor looking part, probably some kind of filter or protection component. When I tried to check the second wire through to its destination I could not get continuity no matter how I approached it, even though that wire looked perfectly soldered to its pad. It sat flat, it had solder around it, and it did not move.
To settle it I heated up my soldering iron, removed all four of those wires, and soldered them back to their pads. And the station came alive.
I want to be honest here, because I never actually saw the fault with my own eyes. My best guess is that there was a hairline crack in the solder joint on that one wire, right at the point where it connects to the external cable going out to the connector. The joint looked physically intact and I would have expected the wire to lift out if it was broken, but it did not budge. My theory is that the hot glue on top was doing the mechanical work, holding the wire in place against the pad so the joint looked fine while carrying no current at all. And this is exactly why the earlier continuity test fooled us. We were probing the wire itself and getting a good reading, so we concluded the wire was healthy, when the break was in the joint between that wire and the pad. This was a first for me, and it is a good reminder that a joint that looks good and even feels solid can still be electrically dead.
Testing the Repaired Station
With the board working I went back to the Python tool to check everything properly. During testing I had explicitly set the station to address 17, so first I used the change address function to move it back to 1 for the demonstration. Then I closed the program and restarted it to show the whole flow from the beginning.
This time the scan on COM 3 found a device at address 1 immediately. The tool then asks what type of device it is, and I selected device type 17, which is the compact weather station with seven measured elements. Reading the data gave me about 27.57 degrees Celsius, relative humidity around 35 percent, and atmospheric pressure of 940 hectopascals. Wind and rainfall both read zero, which is what you would expect from a station sitting on a bench indoors.
The light sensor gave me a nice way to prove the readings are live rather than cached. Sitting on the bench it reported about 80 lux. I moved one of my bench lights to shine directly on the station and read again, and it jumped to 1,230 lux. Turning that light off entirely brought it down to 60 lux, which is just the ambient from my second light. That is real, responsive data.
I also tried the function to clear the accumulated rainfall counter, which completed without a problem, and I looked at the raw view in the tool that shows the exact command being sent and the exact bytes coming back from the station. Comparing that response against the datasheet is how you confirm you are decoding the values correctly rather than just trusting a number on a screen.
Putting It Back Together
Once I knew it worked I disconnected everything and applied fresh hot glue to all the cables and connections, both to hold them mechanically and to give the joints some strain relief. After the glue firmed up I pressed the rubber grommet seal back into the groove in the housing, which is the part that keeps rain out of the electronics chamber.
Then I put the screws back through the PCB and started aligning the two halves of the housing. The critical thing at this stage is not to pinch any of the wires between the sections as they come together. Squeeze a wire and you have created the exact kind of intermittent fault I had just spent the afternoon chasing. I worked the halves together carefully until they seated properly, then added the outer screws.
With the station fully assembled I connected it to the bench supply again. This time it drew 0.01 amps, which is simply the lowest my supply can display, and after zero amps for the entire first half of this project that number was a very welcome sight. On the computer the tool found the device at address 17, I confirmed the device type, and reading the data returned every parameter as expected.
Conclusion
The station is alive and behaving exactly as it should, so we can carry on with the original plan and get it installed where it will actually live. What I like about this repair is how ordinary the fix was compared to how mysterious the symptom looked. No power was reaching the sensor, no address on the entire Modbus range would answer, all the regulators tested fine and every wire had continuity, and in the end it came down to one solder joint that looked perfect and carried nothing. The zero current reading on the bench supply was the single most useful clue in the whole process, and it is the first thing I would check on any dead sensor from now on.
If you have ever seen a wire that is physically attached to a pad but still refuses to conduct, I would genuinely like to hear your explanation, because this one still puzzles me. And if you enjoyed following along with this repair, come subscribe to my YouTube channel so you catch the next teardown.
