Linear Transformer Primary Winding Open
Customer sent to me a Lexco Radio With USB/SD/Music Player with the complaint of no power symptom. I opened up the set and started to check on the linear transformer output ac voltage. It seems to be zero volt and I need to remove the transformer out from the set casing to check on the Ohms reading of the primary and secondary winding.
The Ohms reading of the primary winding must be higher than the secondary winding because the secondary voltage is lower. This linear transformer has the input of 220 vac and output of 6 volt. Please take a look at the two photos below:
When I checked on the transformer winding I found that it was open circuited. This is why there is no output voltage measured at the secondary winding.
For this transformer specification, I kept one used unit and look at the photo below:
Once the transformer was replaced and powered On, the player came back to life again. It was a pretty straight forward repair with no complicating checking involved.
Conclusion- Assuming there was AC output at the secondary winding of the transformer in the beginning of the test then I need to check on the DC output after the bridge diodes. If there is good DC output voltage then I can confirm that the power supply section was working fine and the problem will be lies in somewhere after the power supply section.
If this is the case then it will take a longer time to troubleshoot it. For your information if you are a beginner and wish to learn how to check the linear transformer plus many other electronics components you can check out Jestine Yong’s ebook in Basic Electronics Troubleshooting and Repair.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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Note: You may check out his previous post in the below links:
https://jestineyong.com/standby-led-blinks-in-haier-led-tv-repaired/
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Parasuraman S
December 10, 2020 at 5:44 pm
Good Job!
Arunkant Pandit
December 10, 2020 at 6:28 pm
Dear Suranga,
The transformer primary winding is having thermal fuse. This fuse blows some times due to over heating. Thus shows open primary winding. It can be repaired and saved from going to electronic waste.
suranga Bandara
December 10, 2020 at 10:04 pm
Mr.Arunkant I have replaced Thermal Fuse in many Transformers before this.But the fuse was not found for this type of Transformer. This is a common type.
Dante
December 10, 2020 at 8:05 pm
Hello Suranga,
You say the winding is 0 Ohm. That means a short!
I think it was "open" or endless resistance.
Mason Sarles
December 10, 2020 at 9:42 pm
Very nice. Sadly all the stuff I look at typically has a more complicated problem. Thank you for sharing. Logical troubleshooting path.
Merry Christmas to all!
Kushan Ranathunga
December 11, 2020 at 12:37 am
Great Job Suranga
Yogesh Panchal
December 11, 2020 at 2:43 pm
Another quick fix! Suranga
Humberto
December 16, 2020 at 1:18 pm
Another saved set.