No Power In Panasonic CD RCR Repaired
Customer sent to me this Panasonic CD RCR with the complaint of no power. For your information, the power supply unit inside is from the linear type and not switch mode (SMPS). Because it is from the linear power supply type thus it would be easy to troubleshoot. It is very straight forward, by checking on the ac output voltage you already have an idea where the problem is.
Once the cover was removed I saw few circuit boards inside such as the mainboard, AM/FM unit, linear power supply and etc. Please see the photos below:
When I measure the AC output voltage of the linear transformer I got 9 volt so this indicated the linear transformer is good and there was power coming to the transformer.
After the 9 V AC output there was a fuse and this fuse was open circuit.
This indicates something shorted downstream causing the fuse to blow.
The first component after the fuse were the 4 bridge diodes. The function of this bridge diode is to convert AC to DC voltage. Out of the 4 diodes that I had checked I found two of them were shorted and this is the reason why the fuse was open circuit.
Since two were still good but from experience, it is just a matter of time before these two diodes will go shorted. I have decided to replaced all of them to avoid call back from customer saying the device not working again.
After the replacement diodes was done I powered it up and checked on the DC output voltage and I got 12.23 VDC. I turned around CD RCR and saw FM frequency 88.60 at the front display!
Conclusion- Linear power supply problem is easy to troubleshoot but before that you need to understand how a linear power supply work and you also need to know how to test electronic components. If you still not sure on how to test electronic components I can recommend Jestine’s ebook here. With the knowledge that you have gained from his ebook, I’m very sure you can practically troubleshoot many type of linear power supplies problem in the market.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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https://jestineyong.com/standby-led-blinking-problem-in-tcl-tv-solved/
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Parasuraman S
January 16, 2021 at 9:40 pm
Very good job and thanks for sharing!
Albert van Bemmelen
January 16, 2021 at 9:42 pm
Opening the special constructed plastic housing of these portable audio sets was probably the hardest part. It often also requires using the longest screwdrivers we can get just to reach the inside mounted screw heads, as these sets were not really designed for easy servicing!
Humberto
January 18, 2021 at 3:16 pm
Sure 100% Albert, the longest screwdrivers
Yogesh Panchal
January 17, 2021 at 12:35 am
Good Job! Suranga
Patrick Ribbsaeter
January 17, 2021 at 3:46 am
Very nice job.. thanks for sharing
Waleed Rishmawi
January 18, 2021 at 2:26 pm
congrats on the repair. yes it is always a good idea to replace all the bridge rectifier diodes even not all of them are failing. thanks for sharing your experience with us. keep up the good work and have a blessed day
Humberto
January 18, 2021 at 3:21 pm
Well by you Suranga. Congrats.