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How To Repair Kasa Water Pump
Believe it or not, Australia is the driest consistently inhabited continent in the world. Antarctica is drier, which is even stranger, given that it is almost all ice. However, here in Australia, most properties value the use of rainwater by installing and maintaining rainwater tanks. On our property, 3 separate rain water tanks are used with a total capacity of 10,500 Lt, which is by no means a large amount compared with many other households.
So when the rain water pump refused to pump, it was considered an urgent repair. The pump used in this system is a KASA brand, which is Australian owned, but may be Chinese built. On the front panel of the control box, a failure light could be seen, which was an indication that a fault was present.
The main connector from the control box to the electric motor was a C13 female to 3-pin plug, which is identical to the normal AC cable we attach to the power supply on a desktop computer. To test if the electric motor was working was as simple as by-passing the control box and directly powering up the electric motor.
The motor fired up (this was only done for a short period of time, so that actual pump components aren’t run without water and overheat), so a faulty electric motor could be eliminated from the diagnostic path.
After removing the control box cover, the voltages could be tested. Although the supply voltage was acceptable with 240 volts, only 111 volts could be seen feeding the motor when the ‘on’ button was pressed. Clearly we had a fault within the circuitry in the control box.
This pump uses 2 reed switches to control when the pump is turned on and off, using pressure acting on a diaphragm to move a magnet across the reed switch. Both of these were tested for continuity when moving the magnet across the switches and found to be working correctly.
After testing all the on-board components (diodes, capacitors, resistors etc), the main IC was suspected.
To be honest, I haven’t had a lot of experience testing IC’s, so this was a good opportunity to learn ‘on the go’. The IC to be tested was a HEF4093B which is a Quad 2-input NAND Schmitt Trigger. This is made up of 4 individual, 2 input NAND gates and each input uses a Schmitt trigger circuit. I found the truth table revealed an easy testing procedure that helped me isolate the fault.
After removing the IC from the circuit board and installing it onto my bread board, I was able to make up a testing circuit. By using an LED, I was able to see if all sections of the IC within the circuit were working correctly.
Next, by looking at the datasheet, I could see how the IC was meant to operate. The ‘Truth Table’ showed what outputs would be triggered by providing voltage at certain inputs.
For instance, if 5 volts (high) was provided at the first NAND gate on pin 1 and a low voltage (usually 0 volts) at pin 2, then the output (pin 3) would become ‘high’ or what has been provided as the supply voltage (5 volts in our case).
The only instance where the output (pin 3) would be ‘low’ (or 0 volts in our case), would be when both input pins (1 & 2) have a ‘high’ voltage (5 volts). This function applies to all 4 NAND gates.
In other words, if I applied voltages to both inputs of the NAND gate, the LED on my bread board which was connected to the output through a resistor, should go out.
After using this testing method on the bread board, I was able to see that the 4th gate was not operating and therefore this gave me confidence that the fault was with the chip. However, I couldn’t find a through-hole IC that I could purchase in Australia that would suit the circuit. SMD IC’s were readily available, but I chose to use a complete control box, which was cheap and was delivered to my door within 2 days.
For my own curiosity, I checked the design on the new control box compared to the old one. Most of the changes seemed to be transferring the circuit to SMD’s and an extra varistor had been installed. I assume this was an updated circuit that helped fix some of the issues that the earlier design had.
At this point I decided to also modify the main AC cable. The original installer had made up an extension cord about 400mm long, which didn’t even reach the power outlet! I simply used a spare power cord out of the many that I have collected over the years. I was able to connect this directly to the control box and eliminate the extension cord all together. Making a longer single cable not only made the connection safer, but also less inclined to create poor continuity in the future.
After installing the control box to the pump and the rainwater pipes, priming the water system was necessary to remove any air pockets. After leaving the tap open and activating the pump all air was removed and the system was once again up and running, ready for the next rain to fill the tanks.
If you are interested in this repair, you can see a video on my channel following the link below.
This article was prepared for you by Mark Rabone from Australia.
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Note: You can check out his previous repair article below: