No Power- Bursting Of Optoisolator IC In TV Repaired
This is a continuation of my previous article, https://jestineyong.com/repeated-failure-of-fbt-in-crt-tv-solved/
As mentioned therein, I had put in a lot of efforts to service the TV. But, unfortunately, after about a week, when there was a power surge to the tune of about 400V AC, as a result of which many appliances and electrical fittings in many houses in that area got burnt, this TV also conked off, with a bursting sound from inside. The customer, as you might have read earlier, is a poor guy, who is undergoing a long treatment for kidney problems. He brought the TV to me, and I gave him a standby from my stock. As I had given the TV only about a week back, there was no need for me to subject it to any cleaning.
I opened the set and ascertained to what extent the power surge has damaged the TV. On immediate scrutiny I could not find any remnants of large scale damages. So, dismantled the PCB after taking care of the usual precautions such as discharging the anode cap etc. I could see burnt marks on the bottom plate of the cabinet. Brought the PCB to my work table and looked for what caused the burning marks on the bottom plate. Traced that it was caused by bursting of opto-coupler, two legs of which had melted. You can see the pictures now:
I cleaned up the area at the top and bottom very well. Checked the SMPS Transformer and FBT using my Ring Tester and found these to be OK. Then looked for any defective components in the burnt area. I traced two A1015 PNP transistors that were open and found one IN4148 short. So, replaced these. Looked for any other failure in the SMPS as well as in the feedback circuit.
Could not find any. So, disconnected the jumper to the primary of the FBT, connected a 100W Bulb as load and switched on the TV through a Series Bulb. No oscillation was taking place and the voltage to the PMW IC TDA16846 was missing, with its drop resistor at pin 14 getting hot. A clear indication of defective IC. So replaced it and checked. The 110V was now perfect, indicating that there was no other damage.
Replaced the anode cap, as it was found to be of poor quality, though the FBT was new. Connected the PCB to the CRT and applied power. It was found to be working very well! (Perhaps better than before!)
Here is a picture of the parts replaced:
No, I will not forget to add this last sentence in my article: Thus one more satisfactory job got added to the list, though on the same TV!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 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 repair article below: