SONY TV DEAD repaired
A friend of mine called me to go and check on his TV, Due to my busy schedule I was not able to go immediately and therefore he decided to ask for assistance from a different source (technician).
According to him the tech was coming to check on his fridge, he also mentioned to him about his TV and he said he also repair TVs and hence took on the new assignment.
According to the owner he replaced two components, the STR-S6707 and the posistor. After installed the two components the TV came up very well and after 10 minutes the TV was down again.
The technician figured out that the IC-STR-S6707 might have been poor quality and hence he was back again to the market for another one.
Back again and installed it and fired the TV on and after 5 minutes the TV was down again.
Off to the market now more detailed than before to get a real genuine I.C and back and installed the new I.C.
Pressed the power ON button and this time they only heard the high voltage fire and then dead.
After this third attempt the Fridge/TV technician left in hurry and never came back again.
After hearing this story I made one conclusion, there must be something which is causing the I.C STR-S6707 to misbehave and the most likely cause for this must be a capacitor with has its ESR gone to the roof.
So the first thing I did was to do an ESR test on all capacitors (electrolytic) on the power supply and I bumped on one C623 (220uF/16v) on pin 4 of STR-S6707. This pin is the sink pin of this I.C.
Below is the internal structure of this I.C
Looking at the internal structure of this I.C you can see that this sink pin is very important. It is internally connected to the base of the drive transistor and therefore need to be well filtered of any ripple.
When I tested this capacitor with an ESR meter, my hypothesis was confirmed and I replaced it with a new one.
Please remember in all this the i.C S6707 was not shorting so the fuse was intact, it just stopped working.
After replacing this capacitor it tried powering the TV with the dummy load attached to the B+ and nothing happened so I confirmed the ic was also gone.
I went to the shop and bought a new one and installed it and applied power via the series light bulb and the dummy load on the B+, just to confirm if the power supply is now okay.
After applying power with my eyes fixed on the B+ load bulb, to see if it will light up.
Sadly nothing happened and I concluded that my problems are far from over. One thing I was sure of, the primary power section still has problems.
So I decided to do components test one by one and from experience, I decided to start diode test for shorts.
Having very few diodes on the primary side I got one which was dead short between pin 3 and 2 of the I.C STR-S6707 (D609).
I replaced the diode with a FR series diode which I salvaged from the secondary side of the power supply of another TV board in my workshop.
Now I was sure I have got the final culprit and applied power using the same method and to my surprise nothing happened.
Now frustrated I started doing voltage testing on the primary side and I started with the voltage to the control I.C STR S6707. A quick test on all the pins I was able to get voltages but I didn’t write them down which I should have done.
I disconnected the board from the Set and took it out to do some resistance test for any short on the board particularly on the primary side.
When sitting outside my shop with despair on my face I tried to recollect the voltage on the control I.C STR-S6707.
And here is the actual circuit diagram of the power supply using this I.C STR-S6707.