Hi all,
I battled on this set all day and was none the wiser and thus need expert guidance.
Upon opening the set i noticed it was tampered. The plug wires were soldered direct into the board but for now i won't know if they're a problem. The symptom is that there is no back lights. Flashlight on screen shows the LCD has a picture. I checked the ballast inverter and noticed the following....
The drive voltage is not enough to start the lamps. I used my 100x scope probe to check whats happening. The drive IC is outputting a waveform as follows check "at_first_Xfmer_from_IC.jpg" measuring about 22Vp-p at a frequency of 250KHz. From there i scoped "From_collecor_of_mosfet.jpg" it was about 400V p-p and then i finally took my measuremet at the point where the output goes to the little board that expands the HT to the lamps. At this point my peak to peak is about 250V. Too little to strike the lamps on.
I added a rough sketch showing the circuit without the support components.
With the lamp tester the lamps light up even though this is not a fool proof method of testing them. I can get no info on the drive ic which is a F0711.
Surely the voltage on collector should have gbeen a lot higher on the mosfet where i measured but its not.
I also added a short video to show you what the ballast waveform does on switch on at https://youtu.be/ZVgnLDt__Uk
Can any body guide me better????
Regards
Angelos
I battled on this set all day and was none the wiser and thus need expert guidance.
Upon opening the set i noticed it was tampered. The plug wires were soldered direct into the board but for now i won't know if they're a problem. The symptom is that there is no back lights. Flashlight on screen shows the LCD has a picture. I checked the ballast inverter and noticed the following....
The drive voltage is not enough to start the lamps. I used my 100x scope probe to check whats happening. The drive IC is outputting a waveform as follows check "at_first_Xfmer_from_IC.jpg" measuring about 22Vp-p at a frequency of 250KHz. From there i scoped "From_collecor_of_mosfet.jpg" it was about 400V p-p and then i finally took my measuremet at the point where the output goes to the little board that expands the HT to the lamps. At this point my peak to peak is about 250V. Too little to strike the lamps on.
I added a rough sketch showing the circuit without the support components.
With the lamp tester the lamps light up even though this is not a fool proof method of testing them. I can get no info on the drive ic which is a F0711.
Surely the voltage on collector should have gbeen a lot higher on the mosfet where i measured but its not.
I also added a short video to show you what the ballast waveform does on switch on at https://youtu.be/ZVgnLDt__Uk
Can any body guide me better????
Regards
Angelos
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