This article is brought to you by Mr. Beh. An Electronics repairer based at Tehran in Iran.
The estimated age of this Television is around 12 years of continuous service, No circuit found over the internet.
First I have to tell this TV set was rejected by authorized repair center and brought to me Completely dead with no sign of life, After blowing the inside I checked the Big capacitor by analogue meter set on dc mode 300 v dc
My voltmeter confirms that the 300 volt dc is reaching to the pin of the main capacitor (The red probe to the Positive side of capacitor and black probe to the negative side of the BIG filter cap).
With this I concluded that that all components before the main capacitor like bridge rectifier on /off switch, AC cord are ok and therefore not considered for any further testing.
I checked pin no 6 of regulator ic this is TDA4605 ( by goggling I found the diagram of the ic and the Vcc of this ic that was pin no 6) the red probe of the meter was on the pin 6 and the black probe the negative pin of the Big filter capacitor.
My meter read nothing. Zero volts. Checking the pins of this ic and all surrounding component I found out that there were many cold joints in the low power supply area. I took time and re- soldered them all again.
After that I powered the set and checked pin no 6 of regulator ic and Yes! I got about 11 v dc in V cc pin of ic and is within tolerance. This means the set is getting all the important voltages but to my surprise still TV has no sign of life.
Then is decided to check the secondary side of smps. With my analogue meter I checked the voltages coming out of the smps. This TV has 5V output from the transformer and 5V Schottky diodes, by putting the red probe to the negative (Cathode) side of diodes and black probe to cold ground of the Television.
I checked them all one by one, the voltages were within tolerance and are ok and I was happy up to here. In old CRT TV, usually there are two components that bring problems.
1 HORIZONTAL OUT PUT TRANSISOR (H.O.T)
2 FLY BACK TRANSFORMERS
First I checked the H.O.T by putting my meter on ohm mode x10k (H.O.T in this set is BU508D). D means a diode also is installed in the transistor compartment
And the shape of pins from left to right when the face of transistor is up is B.C. E .And by comparing the reading of meter with new healthy transistor I put ok stamp on this H.O.T of this TV. But what else can cause this problem? The only card remaining is now the fly back transformer?
To test the fly back I used my home made fly back tester which was on my work bench, I checked the pins of this transformer comparing with a good fbt and I concluded that trans former(FBT) is not ok because checker showed two L.E.D were lighted.
Below you can see assembled homemade fly back transformer and expected result from a good fly back transformer (all L.E.Ds) are ON.
I changed with one I had in my salvage stock, After replacing the fly back still there was no high voltage ?...having used my last card I took a break…
See you on the next and last part of this intriguing repair experience
God bless all repairer