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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