How to test my sustain board to make sure my buffers won't be killed?

[tom66]

I repaired a Panasonic plasma TV a few days ago, but hadn't finished assembling it. I think I managed to short something out, as while screwing the side AV board on (while it was switched on - silly silly!) I think I shorted something out because there was a loud bang and a bright flash from the lower Y buffer. When turned on it would do 7 blinks and then shut down. So I removed the lower Y buffer and the set powers on with a picture on the top half.

So I was fairly confident that my idiocy had blown up the board, but then I discovered a crispy insect on one of the buffer ICs! So now I'm not so sure whether or not it was me who killed them, or the insect, or something else.

So if the sustain board is bad, I've heard it can kill the buffers, possibly individually. However I do have a nice picture on top so would that happen with a bad sustain? Obviously I don't want to go out and buy a new buffer only for it to die again.

I have recently acquired an oscilloscope (Gould OS300 20 MHz) which can work up to 400V and have a 10X probe. So I now have the capability to test the scan voltages. I can post waveforms if necessary.

[PlainBill]

Re: How to test my sustain board to make sure my buffers won't be killed?

I repaired a Panasonic plasma TV a few days ago, but hadn't finished assembling it. I think I managed to short something out, as while screwing the side AV board on (while it was switched on - silly silly!) I think I shorted something out because there was a loud bang and a bright flash from the lower Y buffer. When turned on it would do 7 blinks and then shut down. So I removed the lower Y buffer and the set powers on with a picture on the top half.

So I was fairly confident that my idiocy had blown up the board, but then I discovered a crispy insect on one of the buffer ICs! So now I'm not so sure whether or not it was me who killed them, or the insect, or something else.

So if the sustain board is bad, I've heard it can kill the buffers, possibly individually. However I do have a nice picture on top so would that happen with a bad sustain? Obviously I don't want to go out and buy a new buffer only for it to die again.

I have recently acquired an oscilloscope (Gould OS300 20 MHz) which can work up to 400V and have a 10X probe. So I now have the capability to test the scan voltages. I can post waveforms if necessary.

While the Gould OS300 may be a fine instrument, it's about 180Mhz short of what you need to resolve the Y drive waveform.

PlainBill

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

While the Gould OS300 may be a fine instrument, it's about 180Mhz short of what you need to resolve the Y drive waveform.

PlainBill

Well, I gave it a shot, and I *do* see something. Obviously I can't resolve the fine detail, but I can see the individual voltage levels.

I do have a 100 MHz digitising oscilloscope if necessary, but I *really* don't want to blow that one up, which is why I got the Gould.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

Here are some of the waveforms. Do these look okay?

Surprisingly I was able to capture some of the sustain pulses too. However the scope does not have an adjustable trigger hold off (or triggers other than edge and TV), so a lot of other waveforms get superimposed on top.

[rayrod81]

Re: How to test my sustain board to make sure my buffers won't be killed?

The Y-sustain should be fine but the questions is whether the panel is fine or not. There were a couple of Panasonics that would require the entire panel to be replaced if one of the buffers went bad. I have dealt with one of these and the Y-sustain worked perfectly but had a bad buffer. When I replaced the buffer it shorted immediately. I tested the sustain board in another TV and it worked fine. Not saying this is the case with yours but it is possible. The TV that I had was a TH-42PZ77U.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

The Y-sustain should be fine but the questions is whether the panel is fine or not. There were a couple of Panasonics that would require the entire panel to be replaced if one of the buffers went bad. I have dealt with one of these and the Y-sustain worked perfectly but had a bad buffer. When I replaced the buffer it shorted immediately. I tested the sustain board in another TV and it worked fine. Not saying this is the case with yours but it is possible. The TV that I had was a TH-42PZ77U.

Huh. Well, while the TV was working, the bottom was fine. It just went bang while I was testing / assembling it.

The model of mine is TH-42PZ80BA, but I think it uses the same parts as the TH-42PZ77U.

What could go wrong with these panels? No impact damage, perfect picture, no loss of gas as far as I can tell.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

Achievementship and self bettermanship has been created!

A replacement buffer board arrived today (only about £20 - the TV was £50), and the TV is now working, giving a great picture. 1080p 42". I'm tempted to keep this one!

Another TV saved from landfill. A little over 2 years old.

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

The Y-sustain should be fine but the questions is whether the panel is fine or not. There were a couple of Panasonics that would require the entire panel to be replaced if one of the buffers went bad. I have dealt with one of these and the Y-sustain worked perfectly but had a bad buffer. When I replaced the buffer it shorted immediately. I tested the sustain board in another TV and it worked fine. Not saying this is the case with yours but it is possible. The TV that I had was a TH-42PZ77U.

I'm working on a TH-58PZ700U, and I'm concerned that I may have somehow shorted the panel . I pulled the SC board, because the picture would shut down after being on for about 1 hour, leaving just a lit screen. I tested a few mosfets under a heatsink after using a hair dryer to quickly replicate the shutdown issue, but I could not find the failing component(s). So, I reinstalled the board in the TV to see if I could more closely pinpoint the failure.

After I re-installed the board and turned on the TV, I got a totally dark panel (no glow whatsoever). When I turn off the TV, I hear a faint popping sound, but I can't tell from where it's coming. I'm thinking that I may have applied too much heat (although, I tried to be as careful as possible) when lifting the legs of the mosfets to test them. I tried connecting one buffer board at a time, but I still get nothing onscreen. Any ideas? I haven't pulled out the oscilloscope yet.

Edit: I failed to mention that I bought a replacement SC board from a reputable seller, but I still get the same result.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

Do you have an SOS6 or SOS7 blink code?

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

Do you have an SOS6 or SOS7 blink code?

No, I have no blink codes on the front of the TV. I have sound - just an all-black screen, though.

Here are some readings:
- VSUS = 180V on SC board <-- matches the panel label spec
- VE = I'll have to recheck it tomorrow, but I believe I had 155V on the SC board, which matches the panel label spec.
- SS board voltages appear to be correct
- I checked the voltage at the drain of a few mosfets on the buffers, and I have approx 202V.

Like I mentioned previously, what concerns me is that I hear a popping sound every time I turn off the TV.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

VE should be on SS.

Sure about 180V? Very low for Panasonic. Normally 195~210V on these panels. Maybe bigger panel uses lower voltage, I'm not sure.

Popping sound -- try unplugging the speakers and see if you still get the sound.

Panels are pretty hard to short out, as they consist of glass and electrodes.

My personal opinion is you had a bad A or D board and they have now failed completely.

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

VE should be on SS.

Sure about 180V? Very low for Panasonic. Normally 195~210V on these panels. Maybe bigger panel uses lower voltage, I'm not sure.

Popping sound -- try unplugging the speakers and see if you still get the sound.

Panels are pretty hard to short out, as they consist of glass and electrodes.

My personal opinion is you had a bad A or D board and they have now failed completely.

I double-checked, and the panel label says that VSUS should be 180V. Also, yes, the VE 155V was measured on the SS board. I unplugged the speakers, but I still hear the popping sound.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

Tried to locate the sound with a toilet roll tube and patience?

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

It looks like the popping is no longer happening. Also, I didn't notice that the LED on the replacement SC board isn't lit; it was hidden under a large blue poly cap. So, it looks like I need to replace the SC board again, which may or may not correct the issue. I'm pretty close to bailing on this TV.

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

**Update on the TH-58PZ700U**

So, this TV's been sitting for about 6 months until I finally decided to replace the SC, SU, and SD boards all in one shot. Result: The TV still has no picture (screen is pitch black), and the SC board's LED is not lit; VSUS to the board is 180V. The bottom line is that I believe the panel was killed by a faulty SU board based on a more recent conversation with the previous owner . What a waste! The TV had a beautiful picture. It's part of the same family of TVs as the 42PZ77U.

[freakaftr8]

Re: How to test my sustain board to make sure my buffers won't be killed?

with panasonic plasma is usually if the led is bot lit on the sustain it's not generating its proper voltage or something is loading the sustain board down what you try unplugging the c boards and see if sustain board comes up

[freakaftr8]

Re: How to test my sustain board to make sure my buffers won't be killed?

basically even if the panels completely disconnected from the sustain boards you should still have an LED being lit on the board itself

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

Panasonic is one of the brands with which I have very little experience. Since I'm not getting any blink codes, and I have sound, I'm going to continue to investigate.

[tom66]

Re: How to test my sustain board to make sure my buffers won't be killed?

With no image, the SC light may not glow due to the low sustain power (it cuts most sustain fields out.)

[capkid]

Re: How to test my sustain board to make sure my buffers won't be killed?

Progress, err, I guess: I noticed that the cable connection from the DG board to the D board was loose. I now get a brief flash onscreen then the TV shuts down with 6 blinks.

Edit: I just found the attached pages in the training guide, so I'll be performing the included tests.