No Power In Water Filter Machine Repaired
A customer sent this water filter machine to me for repair with the complaint of no power.
The output voltage of this Fuzzy Controller module should be 20 Vdc but now measured zero volt.
Once the cover was opened, I can see the main fuse holder, bridge rectifier, relays and couple of ICs. Just like any other electronic equipment with the complaint of no power, the first component that you need to check is the main fuse.
When the main fuse was tested with my digital multimeter, it had reading and this means the fuse was good. See the photo below:
The next test was the 82 Ohm resistor (Grey, red, black and gold) in which my meter showed that it was open circuit.
I thought one of the bridge diodes should have shorted causing the resistor to open circuit but my guess was wrong because all the four diodes were tested good. One of the diodes reading was .646 which means it was good-see the photo below. Even checking on other major components did not show any bad/shorted components in the circuit.
Since I could not find any shorted components in the circuit I presume only this resistor have problem. So the next step was to find the part for replacement and the part details were 82 Ohm 5% with a 2 watt rating.
Once everything were put back and Powered On, the Fuzzy Controller module came back to life again as seen from the photo below:
Conclusion: If checking the major components did not yield any result, then the next step would be power up the device and perform the voltage test from point to point and obviously will take a longer time.
This article was prepared for you by Suranga Bandara who owns an Electronics shop in Anuradapura, Sri Lanka.
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Note: You may check out his previous repair article in the below link:
https://www.jestineyong.com/videocon-lcd-tv-standby-mode-repaired/
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Ehsan Murad
January 4, 2016 at 12:13 pm
Thank you . Nice step by step directions
Albert van Bemmelen
January 4, 2016 at 4:16 pm
Finding the cause in this Fuzzy controlled device wasn't clear at first, which makes this also a kind of Fuzzy repair (LOL). But professional as always!
Yogesh Panchal
January 4, 2016 at 4:31 pm
Good Job! Suranga,
with good image quality photo.
Paris Azis
January 4, 2016 at 8:36 pm
Hey Suranga
Good job. Well, this is a typical failure in transformerless PSUs (: capacitive input ones). Next to this case (the input resistor failure) the most common is the short-circuited zener diode (I guess ZD 1 in the photo you provided) including some times the filtering el cap. Due to the nature of these power supplies the mains rectifiers fail very rarely! The little magic beyond this is that they work in a “constant current” mode rather than in “constant voltage”. In most cases designers do not even use a fuse based on that…
Another important thing is that this “inrush current limiting” resistor in their input should always be a “flame retardant” type, for a reason which needs no further explanation! But don’t worry! The one you used (an appropriate type of Matsushita Electric, as I see their logo on the replacement resistor) meets fully this requirement!
I put this comment here just because many technicians put any resistor that comes in their hands for sensitive stages like this. And this reflects both their lack of knowledge and (worse than that) lack of responsibility about their work…So, good for you!
Best Regards
Parasuraman S
January 4, 2016 at 9:52 pm
Excellent explanation! Good Job!
Henrique J. G. Ulbrich
January 4, 2016 at 11:31 pm
Problems with resistors generally means "toasted resistors". So, a resistor that simply open with no more apparent cause is quite rare. And unique: no more bad components found! Indeed, a different repair work!
Gary Gemmell
January 5, 2016 at 12:29 pm
You should teach electronics - you have a good grasp of explaining in a simple way with good photos and logical , stepwise refinement!
baishag
January 5, 2016 at 1:07 pm
Thank u so much.. Excellent explanation
Suranga Electronics
January 6, 2016 at 4:46 pm
This is not the first repair. I have repaired this same type of power supply more than 50 units within one year. All units the defective part was 82 ohm resistor only. This is a common fault. I have used the ceramic type of resistor as replacement and so far not even one unit have problem again.