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:
https://jestineyong.com/restoring-a-50-year-old-philips-radio/
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Christian Adzic
February 16, 2019 at 5:04 pm
Hi!
A really well made repair.
Congrat's!
I like the way you done the testing at the end, with the bulb in series.
I have to say, not much technicians take care about safety, they have "no time"
to take some precautions and they don't care what will happen.
This is an effect of the "modern world".
Keep up!
My best regards.
Chris.
Albert van Bemmelen
February 16, 2019 at 7:02 pm
Those too high VAC power surges are very rare in Europe, Parasuraman. And it seems to me that in your country and in other countries as well, using a Belkin Surgemaster (I use several in my apartment just in case!) would be a good idea! Belkin with 6 sockets applies a maximum energy dissipation of 1940 Joule, a maximum peak current of 45,000 Amps and a lifelong Connected Equipment Guarantee up to € 150,000.
Parasuraman S
February 16, 2019 at 11:55 pm
Well! We get such surge protectors, but undependable! Most of them are very cheap Chinese make of poor quality.
Robert Calk Jr.
February 19, 2019 at 5:04 am
Maybe you can take the surge protectors apart and make them more dependable? Assuming that there is enough room inside them.
Lynn Blakely
February 17, 2019 at 2:51 am
Parasuraman: We appreciate your very thorough repair articles. We like to still read the repairs on Jestine's site. I am retired after repairing consumer electronics over 35 years. Yes using the light bulb in place of the fuse is, doing it the right way. Your trouble shooting process is excellent. Knowing how to determine what components are bad is the key to
success.
beh
February 17, 2019 at 3:16 pm
PARASURAMAN
Thank you so much of sending this very interesting article .Indeed you are the number one in electronics in whole sub continent of INDIA.
cheers
behzad
Robert Calk Jr.
February 19, 2019 at 5:02 am
Good job, Parasuraman.
nader bahrami
February 19, 2019 at 3:16 pm
hi
Thank you so much
i from of iran .tehran
Dear friend
It was very good that you also announced the chassis number and the TV model.
You are the No. 1 number of Hindi audio and video repairers
Thankful
nader
Tito Kanshulu
February 20, 2019 at 9:47 pm
Parasuraman, I really like the way you express things in many of your articles because at the end of the day we have all the informaation kept in our brain. keep it up
Humberto
February 27, 2019 at 1:32 am
Thanks for sharing your experiencies. Keep on