Hello
welcome to the world of electronic repair article Today's
topic is how I repair Onida LED Smart TV having a common back light shut
Down-problem. LED/LCD back light issue is common in almost TV'S and LED/LCD monitors.
I
have repaired many N number of TV's/Monitors related to shutdown in my
career. some of them are already published in my electronic
repair article
One
of my friend had a shutdown problem in his Smart TV the model is Onida LED smart 42 inch according
to his input TV will be running around 2 to 3 hours and go to
dark mode but the audio is audible by reciveing this complaint I came to conclusion that it is particularly a
back light issue . Now my concentration is on the back light area of the television.
I gone through the data sheet of the given IC and the topology
involved on LED Switching and parallely gone to the visual inspection for the PCB & noticed the black burning
image under the capacitor which is shown in the photo this is concluded as
a primary clue to accur the fault.
please
go through the below snap for the your understanding.
 |
| FIG1. A burning symptom on the PCB DUE TO MOSFET defective |
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| Fig2.A Typical LED Drive circuit |
According
to the snap and visual inspection tried to debug the reason for the shut down and the culprit could be only on this area.
As
a primary clue checked the mosfet by cold test using my RS115 Fluke multi meter
which is found ok, then question in mind why black burning mark on the PCB???.This is done because SMD mosfet
is mounted on exact opposite side(under side of black mark area).
Even
though my meter reading mosfet found ok I suspected leaky or defective on this smd MOSFET and made my mind
to run the TV to check thermal impact on the SMD surface.
Yes,my
guessing was correct out of 4# two mosfets are getting very hot on it's surface,because of this a burning symptom is clearly visible as shown in fig1. it's a clear evident . When mosfet goes hot resulting excess current drawn and Boost circuit switched off resulting protection mode.Useally this activity will happen in fraction of seconds and very difficult for monitoring with our test instruments. Please go
through the SMD Mosfets Shown below based on above observation finally concluded mosfet faulty.
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| FIG3. SMD MOSFET Getting over hot after 4 to 5 minuets run |
Any
way mosfet faulty was identified but my next task is to replace the same component.
but
unhappy news is that exact mosfet is not available in the market.
Usually
CODES on the mosfets body says the type and typical applications when Googled on an internet.
Now,
I don’t have any option searched equivalent mosfet by referring data sheet,selected and mounted all the four same batch code and type
mosfets as shown with new through hole component IRFU210.
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| FIG4. IRFU210 Mounted instead of SMD Mosfet |
 |
| FIG5. Through hole mosfet Soldered in place of SMD mosfet |
After this started test running about 8 to 10 hours. Back light circuit started working
fine without any interrupt .felt very happy thinking that
this
activity is success and got more
confident because the temperature has not raised even after non stop run after
10 hours without heat sink. Yes,my repair is successes, tv worked perfectly and the back light
section circuit re-gained the life. Finally I re-checked the back Led voltage got 120volt DC which
is normal.
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| FIG6. ONIDA SMART LED TV Ready for Delever after Repair |
Customer felt very happy after watching TV in my
work space and delivered . This is the story how I repaired the 42inch Smart
Onida LED TV. Let us meet in the next
session for one more interesting topic.
With Best Regards
Basavaraj BM
With Best Regards
Basavaraj BM
