Revisit Of LED TV-32PFL3305-V7 After One Month – The Symptoms Of Complaints Can Be Deceptive
In this article we can learn or refresh the following:
1) The symptoms of complaints can be deceptive.
2) Minor noises in the primary switching pulse would not affect the secondary output.
3) Additional filter capacitors added to power supply main line and slave regulators can revive picture clarity to original.
I request you all to see the following link before reading this article, as it will be helpful to know similarities but different reasons.
The complaint reported was that the display went off and bizarre colours and lines were seen, with even audio cut off.
Let us have a look at the extracted pictures of the video that I took upon inspection on my work table:
Now let us compare the pictures posted in the earlier article:
Prima facie the impression we get is panel related or COF related. But believe me, the reasons for such symptoms can be so deceptive that it can lead us to nowhere like a mirage in a desert! Though from the video shared by me in my techie friends whatsup group, many confirmed it was panel or COF related, only one friend who handled panel bonding and lazer treatment, and is an expert, asked me to check the filtering of DC outputs, mainly the 12V. As you might have already read from the earlier article that replacement of all electrolytic caps and dry solder patch up etc. brought back the TV to working condition and solved the no video and video with lines problems. From the comparison of the pictures, you would have noticed that the pattern of symptoms are different. Last time, it had noisy lines in the display along with shifting of colours (RGB) and a few noisy vertical lines. But this time, there were no noisy lines. So, filter capacitors will not be suspected, driving us to conclude it was due to panel related problems. Anyhow, as suggested by my expert friend, I checked the DC wave form in my oscilloscope and it was found to be good enough:
So, I looked at the switching pulses of 3.3V as well as the 12V/24V. The method employed was as suggested by our great Jestine Yong in his SMPS book: Just kept the probe on top of the SMPS transformer without connecting to the hot ground. (Caution: Do not connect oscilloscope in the primary area to hot ground, without using an isolation transformer either for the device under testing or the oscilloscope itself. Otherwise it will trip the ELCB of the mains control panel, as the ground of the oscilloscope is connected to Earth in of the three pin 230V AC) The result was not satisfactory as ripples were seen in the 3.3V switching and the pulses of 12/24V switching were not proper:
What you see above is the primary switching of 12v/24V pulses. Though I remember to have clicked the noisy switching of the 3.3V, I could not locate it among the 107 snaps and many videos taken.
Click here to check out the LED TV Panel Repair Ebook
Anyhow, this made me comb the PS primary section and there were surprise findings. The two box type capacitors used in the EMI section of AC input were showing readings that showed shorting. The 105 fixed cap (1uF/450V) connected across the positive and negative outputs of the bridge rectifier was showing such a reading that it indicated the possible cause for the disturbing pulses:
The first cap above is 684K, second one 474K and the last one 105J. The last one could cause problems as it was across the positive and negative output of the bridge, as already mentioned. So I replaced these caps and checked the wave forms once again and found these to be normal in acceptable levels though a couple of spikes at different times were found in the 12V/24V switching. Let us have a look:
The first one is 3.3V switching and the second one is that of 12V/24V switching. After removing and checking the other components in the primary and secondary, I connected a 1 K resistor from 3.3V to the Power On and another 1 K resistor to the Back Light ON and applied power. I did this to check the behavior of the Power Supply on load of the LCD backlight. This time a new problem was noticed. The backlight got off on its own after a few minutes. This is a new problem in a different part of the TV, as it had an LCD drive board fit vertically in the right side end. Only the 24V, Backlight On and DIM were going from the PS Board to this Board. The LCD driver board had two ICs in it. One was the oscillator OZ9966SN another was FP5150, datasheet of which could not be obtained. But AI indicated that FP5150 is a DC to DC converter. As only 24V was going in and the OZ9966SN had 12V as VCC, this IC presumably is the DC to DC converter. Following is the picture of the LED driver board with four outputs going to the four LCD backlights:
You all can perhaps understand my predicament. TV was given with one problem, which is becoming multiple day by day. Anyhow, like a good doctor, who wants all the inherent diseases to surface when admitted to the hospital so that all can be cured or controlled, my initial dis-enamor vanished and I too wished that the TV completed all its bad time when it was in my custody. Since the VCC was ok and I had replaced all the four 270uF/35V caps with 330uF/35V, though they did not show any defects on checking and the backlight problem persisted, the only possible reason was weak LCDs that were drawing excess current, which the IC detects and shuts down. Let us remember that this TV was 12 years old and something like this is definitely expected. So, the shortcut method was to cut off the protection.
Looking at the data and studying various videos related to the IC, pin 15 which is shown as timer and grounded with an SMD capacitor was to be connected to the ground through a 10K resistor, which I did. Then the backlight remained lit and the IC was not getting hot, indicating that the problem was not major. After making sure that the backlight was ok, I wanted to make sure that the panel was ok. I connected a U11 board (use of which has been explained by me very well in my previous articles, one of which can be seen here: https://jestineyong.com/fixing-u11-board-in-samsung-ledtv-la32e420e2r-restoring-backlight/ ) and I got a picture like the first image given below, which got set right after changing the setting of LVDS connection:
This defect is called picture mapping and can be resolved adjusting the resolution suiting the panel and/or the options shown under the LVDS connection, through settings. I allowed the TV to run in this condition for quite some time which proved that there was nothing wrong with the panel. Then removed the U11 and connected the original mother board and found that the picture was good enough now, but the backlight flickered and got off. I had already removed the 1K resistors when the PS board was connected to the mother board. Since something was going wrong with the control from mother board, I removed the BL on wire from the connector and connected a 1 K resistor like before and tried.
Backlight was on but it flickered. Then I removed the DIM wire also from the connector, upon which the backlight was steady. The TV was checked to be working very well. Anyhow, in order to make doubly sure that there should not be a problem soon again I carried out adding filter capacitors in the primary 12V supply as well as in the secondary slave regulators such as 5V, 3.3V, 2.6V etc. as per advice given by one of my techiefriends. First I fixed a 1000uF/25V cap on the 12V supply at the point where it entered the mother board, as there was a provision for that. Then added 100uF/25V at the input and output on regulator ICs wherever higher rated IC was found used. Then added 10uF/25 at the in/out of other regulators found on the mother board. Let us have a look of this conglomeration of capacitors.
One has to be careful in selecting the ground for the capacitor, as in some regulators which are adjustable type; there would be resistors from positive and negative rail to adjust it to the desired output. So, we should not mistake it for ground. After this work, the mother board looked like a patient who underwent surgery and wore extra fittings after a bizarre accident with multiple fractures! Anyhow, the result was so damn good that I patted myself on the back without my wife seeing, lest she should confirm her doubts about my crazes! (LOL) The picture was so clear that I could not believe my eyes! I also shared this with my techie friends and thanked them profusely for all the help offered. As one of the regulator ICs (3.3V) was getting hot that supplied power to the uController to the portion which handled the video section, I replaced it with an externally fit better current rated IC with a separate heat sink as per images shared below:
(The picture of the newly fit IC was taken before I fixed two 10uF/25V capacitors at the in and out) As the IC I used was a fixed 3.3V and in the board it was an adjustable type, I connected the first pin to the ground directly. The new regulator was fixed safely on double sided thermal conducting tapes that we usually use for LED backlight fixing. Having completed my marathon tasks successfully, I allowed the TV to run for several hours before giving delivery and fixing it in his home. I told him to pay my charges only if it works at-least for a week without any more problems, to retain the confidence he has bestowed on me and to avoid a reprimand from my elder brother, who was the customer’s classmate.
In order to close the work order, I confirmed that the TV was working very well at the customer’s place, by calling him up next day. Now can I say another tough mission got accomplished with multiple satisfactions getting attracted by the collection bag?
This article was prepared for you by Parasuraman Subramanian from India. He is 76 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous article on The Thrill Of Assembling A Discreet Amplifier
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