How To Repair Mixer Power Amplifier
The complaint of this UKC Mixer power amplifier was no power. The first component to check is the main fuse but it did not blow but the toroidal was very hot that it melted the plastic cover-see the photo below:
What caused the transformer to overheat? It will be surely a component that is shorted that had caused the transformer to go overheated.
From visual inspection of the mainboard, there were no burnt components-see the photo below:
But when I checked on the bridge rectifier on board, i found that it was shorted-see the photos below:
I do further testing on some other major components and all seems to be in good condition.
I concluded that it was only the bridge rectifier that was shorted and the result was an overheated toroidal transformer.
I found a replacement and the part number is RBV-406M and the rating is 600 volt with 4 ampere.
Once the replacement was done and powered On, the mixer amplifier came back to life-see the photo below:
Conclusion- In this case, there was only one faulty part and it didn’t take me long to finish the job. If you wish to learn how to check components so that you can start to troubleshoot electronic equipment you can check out Jestine’s ebook here. It comes with many photos to guide you how you can check electronic components the professional way. Ok see you in the next post soon.
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-problem-in-pioneer-mini-hi-fi-system-repaired/
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Parasuraman
January 26, 2018 at 11:55 pm
Very good!
AdamS
January 26, 2018 at 11:56 pm
Nice repair Suranga, but disappointing there were no fuses on the transformer outputs - bad design!
Albert Hoekman, Holland
January 27, 2018 at 2:05 am
Good article and fine pictures, thanks for sharing.
What about the transformer? Are you not afraid the transformer has some shorted windings?
Henrique Jorge Guimarães Ulbrich
January 27, 2018 at 5:20 am
If the bridge rectifier was completely short, the fuse would have to be opened. Why this did not happened?
Imraz
January 27, 2018 at 5:25 pm
Possibility of a high rated fuse installed before it reach the repair desk
Henrique Jorge Guimarães Ulbrich
January 29, 2018 at 10:08 pm
Yes, Mr. Imraz. I don´t believe the fuse is original. Obviously, the manufacturer did the right. Later, a bad technician changed this situation.
Albert van Bemmelen
January 27, 2018 at 5:45 am
Indeed a lucky customer finding only a bad rectifier bridge being defect. And a successful repair. Strange though that it only caused the transformer to overheat without blowing any primary or secundary fuses, or worse causing fire. Especially seeing it is an expensive professional audio set.
This way it looks like being designed quite unsafe which is the reason why fuses are used. The question always remains if we should alter the original design. But I guess it won't harm to warn the owner why he was lucky this time. And maybe change the 'safety' of the circuit by adding fuses or adjust their values if the owner appreciates the extra time that is involved to change it. Including some experimenting time necessary to check if the changing of the fuses works. A fuse is less expensive than a new transformer.
Tyrone.
January 27, 2018 at 6:24 am
Very good Suranga.
Robert Calk
January 27, 2018 at 10:42 pm
Good job Suranga.
Ulises Aguilar Pazzani
January 30, 2018 at 11:49 am
Mr Suranga grate job Sir
Adekunle Adegoke
September 7, 2020 at 11:58 pm
Please my mixer amplifier power indicator light is blinking and sound is not coming out.