How To Fix Active Speaker- No Power
This nice designed Polytron active speaker came in with the complaint of no power and my customer wants me to fix it for him.
The first thing I do was to test it first before opening the cover. Yes, it was indeed no power and I had to open the cover to repair it.
Once the cover was removed, I could see the power supply and the amplifier circuit board. The main fuse did not blow so this means usually the bride diodes were also good.
I proceeded to perform the on board voltage test at the power supply output pins. The power was turned On and I placed my meter’s red probe to the output pin and the black probe to cold ground. The voltage reading that I’d got was fluctuating. Even pulling out the white cable from the connector, the result were still the same (fluctuating voltage went up and down).
I knew it was the power supply (SMPS) fault but I just could not find any bad components in the primary and secondary side. The only components left to check were the 2 pieces Optoisolator IC and the TL431 IC.
These ICs can actually breakdown when under load so checking them with an Ohmmeter will not guarantee that they are good. The best is to replace them and retest.
I replaced the three ICs and to my surprise the power actually came back- see the photo below:
If you want to learn how to be good in switch mode power supply repair you can check out Jestine Yong’s SMPS repair ebook HERE.
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 about fixing active speaker article in the below link:
https://jestineyong.com/how-to-repair-active-speaker-matsutec-brand/
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Parasuraman S
August 12, 2016 at 8:29 am
Good Job! Replacing the TL431 and opto-couplers proved what an expert you are!
sudhir
August 12, 2016 at 1:37 pm
good work suranga
please keep posting as your troubleshooting skill are great and helps in understanding the repair.
your best part is your presentation which is nice and informative.
once again thanks for your post
Suranga Electronics Sri Lanka
August 13, 2016 at 12:49 am
Thanks Mr,sudhir
Albert van Bemmelen
August 12, 2016 at 1:45 pm
Thank you Mr. Suranga Bandara for the given conclusion that the TL431 and the Optocouplers can breakdown under load. I have a digital tester for those components which would mean that maybe my device mistakenly could test them to be good when they aren't.
I hope I never had that happening yet!
Suranga Electronics Sri Lanka
August 13, 2016 at 12:50 am
Hi. Thanks Mr.Albert
Yogesh Panchal
August 12, 2016 at 3:03 pm
Suranga,
Good Repair,
Luciano Khware
August 12, 2016 at 6:53 pm
Great troubleshooting skills Mr Suranga!
Mark Tembo
August 16, 2016 at 8:39 pm
Thanks, and I like your post!
ombra32
September 5, 2016 at 7:04 pm
Great work!
Justice cele
June 15, 2017 at 7:18 pm
Informative repair knowledge thanks.