Hi,
I recently bumped my old thread about LG PDP (42V6) problems, but as I solved these problems and a completely new, unrelated problem occured, I decided to create a new topic.
If you could look at this short movie: http://youtube.com/watch?v=Q6qK7zMrJaA
I recorded how the "No Signal" frame is erased with a 60 FPS camera and stretched it, so the frames can be visible. It is clearly visible that something is wrong with the erase.
Of course, I made adjustments. I have set the voltages according to the sticker on the panel. They read:
Va: 65V
Vs: 190V
V5V: 5V (VR turned to the minimum, should be less in this position...)
Vsetup: 200V
-Vy: 70V
Vscw: 110V
I have also made set-up and set-down adjustments (set-up 20us, set-down 150us, as in service manual). See attached pictures for the oscilloscope screenshots. There are two pictures for set-down ramp (I currently left it as on the second picture, setdown2.png - note the vertical cursors and measured period in the top left corner), which leads to my first question.
Look at my set-down waveform. It's clearly different from the one found in the service manual, as after the set-down phase, the voltage should immediately rise from -Vy to Vsc-Vy (referred to ground), but in my case there's a dead time between set-down ramp ends and another pulse begins. Also, this pulse is much longer in the service manual than in my PDP. It was the same with my old, broken YSUS (which actually was working, but only with a bright picture)... it seems unlikely that both YSUS boards are broken in the same way, maybe the driving signal from the control board is different due to different firmware, or something? Would you suspect both of my YSUS boards to be broken, or maybe would you leave it as it is (and if yes, as what picture - setdown1.png or setdown2.png, because I don't know if I should measure this ramp with this dead time or without)?
My second question is about ZSUS board. When I try to measure its waveform, I cannot find the Z ramp, mentioned in the service manual. According to it, Z voltage should rise for 2us from 0V to Vs, stay at Vs for 7us and then rapidly fall to 0V. There is a signal there, but I cannot observe anything like that, no matter how I set VR3 (regulation VR on the Z board). It just ignores VR3. Also, regulating VR3 has no visible effects on the image (I tried with different images - 100% white, actual picture, "no signal" frame etc). Should it produce some visible effects on the picture?
When I set set-up stage to last for 50us, the screen gets brighter, but these dots no longer occur. But I suspect it's not the solution.
Do you have any advice? I am thinking about replacing ZSUS, but I want to be 100% sure it's dead. I checked ZSUS IPM with a diode checks and all checks went OK.
Regards.
I recently bumped my old thread about LG PDP (42V6) problems, but as I solved these problems and a completely new, unrelated problem occured, I decided to create a new topic.
If you could look at this short movie: http://youtube.com/watch?v=Q6qK7zMrJaA
I recorded how the "No Signal" frame is erased with a 60 FPS camera and stretched it, so the frames can be visible. It is clearly visible that something is wrong with the erase.
Of course, I made adjustments. I have set the voltages according to the sticker on the panel. They read:
Va: 65V
Vs: 190V
V5V: 5V (VR turned to the minimum, should be less in this position...)
Vsetup: 200V
-Vy: 70V
Vscw: 110V
I have also made set-up and set-down adjustments (set-up 20us, set-down 150us, as in service manual). See attached pictures for the oscilloscope screenshots. There are two pictures for set-down ramp (I currently left it as on the second picture, setdown2.png - note the vertical cursors and measured period in the top left corner), which leads to my first question.
Look at my set-down waveform. It's clearly different from the one found in the service manual, as after the set-down phase, the voltage should immediately rise from -Vy to Vsc-Vy (referred to ground), but in my case there's a dead time between set-down ramp ends and another pulse begins. Also, this pulse is much longer in the service manual than in my PDP. It was the same with my old, broken YSUS (which actually was working, but only with a bright picture)... it seems unlikely that both YSUS boards are broken in the same way, maybe the driving signal from the control board is different due to different firmware, or something? Would you suspect both of my YSUS boards to be broken, or maybe would you leave it as it is (and if yes, as what picture - setdown1.png or setdown2.png, because I don't know if I should measure this ramp with this dead time or without)?
My second question is about ZSUS board. When I try to measure its waveform, I cannot find the Z ramp, mentioned in the service manual. According to it, Z voltage should rise for 2us from 0V to Vs, stay at Vs for 7us and then rapidly fall to 0V. There is a signal there, but I cannot observe anything like that, no matter how I set VR3 (regulation VR on the Z board). It just ignores VR3. Also, regulating VR3 has no visible effects on the image (I tried with different images - 100% white, actual picture, "no signal" frame etc). Should it produce some visible effects on the picture?
When I set set-up stage to last for 50us, the screen gets brighter, but these dots no longer occur. But I suspect it's not the solution.
Do you have any advice? I am thinking about replacing ZSUS, but I want to be 100% sure it's dead. I checked ZSUS IPM with a diode checks and all checks went OK.
Regards.
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