Futile Attempt To Revive Onix LED TV Model Crystal 40
One fine morning I had a surprise call from an unknown person introducing himself quoting a few references stating that he was a technician of different field and he could not resolve a problem of shorting he found out in the 3.3V input area because of which the TV was dead. He worked abroad and was on leave for a few days and wanted to fix it urgently.
Well, my curiosity got aroused and I gave him green signal to come over. As I suggested bringing the TV instead of the board, he brought it. I opened the back cover of the TV and followed what the troubleshooting was done by him. The 3.3 V input to an IC was dead short. Let us have a look at the board which combined power supply and processor together.
The IC for which the 3.3V input has to come is shown below (unfortunately the picture is not clear enough to read the number) and the Mosfet that supplies the voltage is shown on its side:
The input area was dead short. Even though this gentleman spent several hours trying to locate the short, he was not able to find it out because of the absence of a schematic diagram and mostly because of lack of time as his leave period was packed with social visits and other engagements. Anyhow, I cut the input to the IC and checked and found out that the input itself was shorting. Then I checked the input of the Mosfet and that was also short. So, the 5V area itself was short! I used analogue multimeter (X1 range) which is the best to use for such troubleshooting. We can check diodes, transistors and Mosfets using the Analogue Multimeter and can even check for any short or leak of fixed capacitors too.
Jestine Yong always suggests use of this Multimeter in his repair books. I told him to leave the TV with me for extensive tracking and requested him to attend to his essential activities during the short period of his leave.
I removed the adjacent capacitor and tracked where the rail of the 5V was going to. I removed all the three remaining large capacitors also in order to track. After spending several hours of tracking, I located that the track was split into two. I cut the track that was going towards inside of the main IC area. The short remained. Then tracked the other line and traced it reaching behind the USB socket. There was a zero ohm resistor in the track and I removed it and found that the short in the Mosfet area was removed, but remained at the other end. There was a very tiny capacitor at the other side which was a filter capacitor to the ground. On a sheer intuition, I just removed it. The short had gone at-last!
The tiny capacitor jumped out of the tweezer and fell somewhere and I lost it. Anyhow that did not matter as it could be a low value filter. The yellow arrow in the following picture would show you where the ‘vagabond’ capacitor was!
Then restored the rest of the cut tracks and applied power. The output was pulsating indicating that either there was a problem in the primary area or there are some more leaky caps or components on the board. As he had come home for a follow-up visit as per my call, I showed this to him and told him that I would try tracing the culprits in the board and let him proceed with his tight schedules. I replaced the 10uF/50V capacitor in the primary as that was a key component that could cause problems. Then removed and checked the fixed capacitor that filters the switching in the primary area.
It was found ok. Following is the Switching area picture along with a rough sketch I drew to track problems in the area:
I checked each and every component in the primary area and everything was ok. The voltage to UB101 switching IC was also present, which anyhow was obvious as the PS was getting on. Then I turned my attention to the secondary side and combed the entire area for any leaky or shorted components and could not find any. In the process I drew a sketch of the TL431 IC area as well:
I kept reporting the progress to the customer and took his clearance to do a do or die test in the board. The most difficult problem was that the PS was combined. If PS was separate, we could have easily found out the problem without causing damages to the mother board. Here we stand a chance and precisely that is what happened. I wanted to use a four wire module (5-24 board about which I have already covered in many previous articles – Just see:
https://jestineyong.com/a-five-wire-str-module-did-not-work-in-this-aoc-lcd-monitor-model-tft15w60ps/ ) and check whether the secondary was working and connected it. The advantage of such a test was that if any of the components or areas are having leak or short on switch on, that will fume and we can easily locate it. That is why we call it the do or die test. I removed the SMD switching IC and Mosfet from the primary and connected the external PS board. Following is the picture of the board, primary control of which is taken over by the separate board:
The SMD optocoupler 817 was replaced beforehand with a new one for ensuring that there was no mistake in the feedback. The pins of 3 & 4 of the opto in both the boards were lifted up Then the pins 3 & 4 of opto in the combo board was connected to the external board where its 3 & 4 was connected. A type of bypass connection so as to ensure that the voltages for the combo board were generated and controlled as how it was designed for. I have done this many times before and reported in my articles before and I am not repeating it in full details again. Then when I powered it up, the serial bulb lit indicating that there was some short somewhere. The audio IC (RDA3118E28) fumed within microseconds indicating that that was the culprit. One 470uF/16V also bulged a bit, which I replaced later.
Though I removed the IC, I was feeling that there were problems in the board elsewhere too. Though I combed the entire board using the analogue multimeter, I could not find any direct short. I removed the external PS board and connected a three wire module (once again already covered by me in many previous articles and hence not repeating its use – Just see: https://jestineyong.com/cracked-unknown-pwm-replaced-by-universal-module-in-pressure-monitorsmps/ )
But no output came on switch on, indicating that the board had failures elsewhere also. I removed the module and put back the removed components and applied power to see whether some miraculous revival would happen. But nothing happened except a couple of shocks that I got from the tank capacitor as I forgot to discharge it before working on the primary area!
Further investigation was abandoned as advised by the customer and the board was put back like before and back cover closed for pick up by the customer, which he did the next day. As he was a technician, he was planning to replace the board with the latest android smart board and upgrade it.
So, several hours of my toil and burnt night oil resulted in utter fiasco! Nevertheless, can I have satisfaction collected to the bag? It is for you readers, to decide and it is awaiting your nod to enter! (LOL)
This article was prepared for you by Parasuraman Subramanian from India. He is 74 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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Tree
August 16, 2025 at 6:11 pm
Verygood sir.
Parasuraman S
August 16, 2025 at 8:39 pm
Many thanks!
Albert van Bemmelen
August 16, 2025 at 7:24 pm
Although this failed repair attempt did not originate by your doing it qualifies to be databased in a special bag labelled "unfixable comboboard designs" (lol).
Parasuraman S
August 16, 2025 at 8:43 pm
Ha! Ha! Enjoyed! Many thanks, dear Albert!
Waleed Rishmawi
August 16, 2025 at 7:25 pm
wow, that was time consuming adventure and a lot of hard work but I enjoyed your detailed investigation of the problem. for the short on the 3.3 voltages I would have used a thermal camera that that would save you a lot of repair time. it is worth having. sometimes we has techinicans we have to stop and evaluate the situation then replace the whole board instead of repairing it. thanks for sharing and have a worderful blessed day my friend. I really enjoyed your article.
Parasuraman S
August 16, 2025 at 8:44 pm
Thermal camera is something that I cannot afford to buy at the present juncture. May be, if luck favours, I can get it added. Many thanks for your comments, dear friend!
Mohamed Kikia
August 17, 2025 at 1:57 am
Thanks for sharing. I've been in many situations like this where it's not economically viable to repair a board but the technician in me refuses to give up! We do however have to call it quits at some point. It's just a tech's life!
Parasuraman S
August 17, 2025 at 10:58 am
Yes, I fully agree with you! The thrust out of a satisfied result is what makes us going! Many thanks for your comments!
Mark J
August 17, 2025 at 8:01 am
Parasuraman I will still give you a nod to enter the satisfaction bag. Thank you for sharing.
Parasuraman S
August 17, 2025 at 10:58 am
Oh! That's very nice of you, dear Mark! MANY THANKS!
Muykit
August 17, 2025 at 9:40 pm
Yu caried on frm wher th client left, it ideally exemplifies - when the going gets tough, the tough get going. Hats off to you. Now allow me to adres him. Mr. Expert, it calls 4 quite a measure of troubleshooting trickery and vast knowledge in elctrnics for anyone to precisely establish, like in ths case, tht ther is a shot in th 5v outpt circut. Ths 5v frm smps trnsfmer is reglatd acrately by ICs, & goes 2 amng othr cmpnents, th micro-controller. Anothr contrl crcit wth ICs; 817, 431, th trnsfomr swtchng IC and its drver IC, capctrs, resistrs and what have you, also oversees th trnsformrs 5v/curr outpt. So failure in any of thes crcuit compnents may alow th outpt voltg or CURRENT flw to go overboard or b non existant in the 5v output circuit. But above all the microcontroller is the main watchdog that should never look the other way when indeed it should initiate a complet systm shutdwn wen such exesive voltge or curent is detcted. Faulty Micro- IC remval, makes many Mr Experts look 4 profsionals !
Parasuraman S
August 18, 2025 at 4:18 pm
Many thanks for your detailed comments!
Yogesh Panchal
August 17, 2025 at 10:24 pm
Sir,
When someone already tried on the device,they make it time consuming job,because every technician having their own way to troubleshoot.
off course it has never been failure you got some new experience to put in your bag.We all know every device is not fixable because of some limitation.
Parasuraman S
August 18, 2025 at 4:19 pm
Yes, indeed true! Many thanks for your encouraging comments!
Imoud.O
August 18, 2025 at 5:54 am
I repair a lot of this type of tv with combo motherboard and I have come to realise that this type of board once it starts having defective component, it continues having problems,components breaking down one time or the other even after repair and customer keeps coming back unsatisfied.
So as result of this,I now advise customers to replace the board with new one for sustainable result
However i give you a round of applause for your efforts to bring it back to life.Your bag may not want to receive this kind of satisfaction this time around,since it welcomes and receives'complete satisfaction' only I guess LOL. Have a nice day.
Parasuraman S
August 18, 2025 at 4:21 pm
Ha! Ha! Many thanks for your loving comments, dear Imoud!
Muykit
August 18, 2025 at 6:02 am
Its wise of you to acquire more useful modern tools. But as for me most of the tools are far beyond the bounds of affordability and I have to make do with what is within reach. Old is gold, ever so often I'm inclined to revert to the old manner of troubleshooting a power or sound IC, by saliva-wetting a finger tip then tapping the finger tip on the ic pins while listening for any crude sound from the speakers, or by testing for voltage or continuity with a test lamp. By the use of human senses, eyes help to judge a marginal or drastic drop of the bulbs light intensity that translates to voltage drop. A dimmed light may indicate an abnormal voltage drop that calls for investigation, in as much, a hot to touch IC. Old habits die hard. In other fields like automobile electronics, some old specialized repairers have never used a multimeter, and so beside experience, they heavily rely on merely a test lamp and a wire cable for troubleshooting. How they turn out to be special repair achievers, only hell knows.
Parasuraman S
August 18, 2025 at 4:22 pm
Yes, very true! Thanks again for your detailed analytical comments!
Wayne
September 2, 2025 at 6:51 pm
Great staff!