LG 60PZ750 running hot and maldischarged

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Any chance one of the transistors I replaced could be defective or over heating, would that cause this ?

[tom66]

Re: LG 60PZ750 running hot and maldischarged

It's possible, which is why we need to see what's happening on the scope.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

I don't have an experienced eye but what does seem to change is the thickness of the vertical wave, seemed to get thinner ?? Below are a couple of links.

https://www.youtube.com/watch?v=P4kxFZIaTSU

https://www.youtube.com/watch?v=mHM3ycuSHHc

Yeah - looks odd

Can you try setting the panel on a fixed colour pattern so that the waveform doesn't change - you could use something like MS Paint

Then observe the waveform and see if anything happens to it as the fault develops - a video of the waveform may help me here

[freakaftr8]

Re: LG 60PZ750 running hot and maldischarged

Are you certain of the inductor coils on the ZSUS making a good contact? And of course all screws are tight? This board uses floating grounds.

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Setting your oscilloscope trigger to normal may also help keep the waveform more stable, as would changing the volt scale so you can see more detail.

But as Freak says I'd check inductor soldering.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

When I repaired the board I checked the coil solder points on the board and they actually looked pretty good, only a couple had small hair cracks so I did resolder all 6 points. I will reheat the joints and re solder again today.

Are you certain of the inductor coils on the ZSUS making a good contact? And of course all screws are tight? This board uses floating grounds.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

I resoldered the coils and the transistors I replaced and all screws are in tight. And the TV does the same thing. It seems there is a component on the board that once the TV runs for 10-15 min it begins to fail, I am no expert but I am thinking a resistor or diode ???

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

any chance one of the inductor coils could be bad ? Also is it normal for the heat sinks with the IGBT's to be over 200F after running for 15 min ?

Are you certain of the inductor coils on the ZSUS making a good contact? And of course all screws are tight? This board uses floating grounds.

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Those heatsinks sound quite hot...
I would use your scope to further investigate the waveform thickness issue, as you mentioned above, using the NORMAL trigger and pan/zoom controls...

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Could you step me through that, scopes are still very new to me. Thanks

Those heatsinks sound quite hot...
I would use your scope to further investigate the waveform thickness issue, as you mentioned above, using the NORMAL trigger and pan/zoom controls...

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Set your scope to NORMAL under trigger settings, all other settings as before.

Zoom into one of those sections that has a "burst" in it - the bit moving rapidly between voltage. I'll highlight it if you need, but no software atm. Zooming in the horizontal axis is accomplished using the timebase dial and the horizontal position. Hard to describe exactly what you're doing, but it comes naturally pretty quick. You'll want to be able to see the individual up and down parts of the waveform - a "square wave" http://recordingology.com/wp-content...quare-Wave.gif although it'll look a bit more rounded than this)

We'll want the screen to be showing a static white / shade of grey / picture on it until the fault shows (be aware of image retention - 20 minutes static image should be ok, but no longer without having something else on screen first)

Then just watch to see if anything happens, see if you can correlate changes on the screen with changes in the waveform, if you don't know what you're specifically looking at feel free to take a video of it.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

When I put the scope trigger to normal the readings on the scope disappear, also I can't seem to get a square wave when on auto.

Set your scope to NORMAL under trigger settings, all other settings as before.

Zoom into one of those sections that has a "burst" in it - the bit moving rapidly between voltage. I'll highlight it if you need, but no software atm. Zooming in the horizontal axis is accomplished using the timebase dial and the horizontal position. Hard to describe exactly what you're doing, but it comes naturally pretty quick. You'll want to be able to see the individual up and down parts of the waveform - a "square wave" http://recordingology.com/wp-content...quare-Wave.gif although it'll look a bit more rounded than this)

We'll want the screen to be showing a static white / shade of grey / picture on it until the fault shows (be aware of image retention - 20 minutes static image should be ok, but no longer without having something else on screen first)

Then just watch to see if anything happens, see if you can correlate changes on the screen with changes in the waveform, if you don't know what you're specifically looking at feel free to take a video of it.

[tom66]

Re: LG 60PZ750 running hot and maldischarged

OK that's odd, are you triggering off CH2 with CH2 connected to VS_DA? If it has a stable waveform in AUTO mode, then NORMAL mode should work just the same. All AUTO mode does differently is if the waveform appears less frequently than the oscilloscope expects it automatically fires a trigger anyway, so you always see a waveform there (useful for initially setting up the scope or doing quick tests). So NORMAL should work fine if the waveform is stable...I guess, just check your connections and setup again. Post a picture of the trigger settings menu on your scope if you're unsure of what you're doing.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

For ch2 the VSDA probe should it be set to 10x on the probe and ch2 set to 10v/div ?

OK that's odd, are you triggering off CH2 with CH2 connected to VS_DA? If it has a stable waveform in AUTO mode, then NORMAL mode should work just the same. All AUTO mode does differently is if the waveform appears less frequently than the oscilloscope expects it automatically fires a trigger anyway, so you always see a waveform there (useful for initially setting up the scope or doing quick tests). So NORMAL should work fine if the waveform is stable...I guess, just check your connections and setup again. Post a picture of the trigger settings menu on your scope if you're unsure of what you're doing.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Also the only way I can get the trigger to work in normal mode is when the source is set to "AC Line"

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

My scope setup :

Ch1 turned on, probe set on 10x, v/div set to 10v and probe on output of zsus board

Ch2 turned on, probe set on 10x, v/div 10v and probe on control board vs_da

Both probes ground clips on grounded screws

Trigger source set to channel 2

Trigger type is Edge

Trigger on auto (I can't put it on normal with this setup, screen goes blank)

Slope is Rising

Horizontal time 500us

Turn on TV with blank white screen

[tom66]

Re: LG 60PZ750 running hot and maldischarged

CH2 needs to be 1V/div and trigger level at about 2V. Rising edge. 10X is fine as long as scope is also on 10X. You should check CH1's 10X mode is set correctly. Recall previous instructions where both probe and scope need to be on 10X to get correct readings (so oscilloscope scales them correctly)

AC line trigger uses 50 / 60Hz mains voltage as a reference, it is not useful for this application but has uses in power supply repair etc

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Ok, How do these look ?

CH2 needs to be 1V/div and trigger level at about 2V. Rising edge. 10X is fine as long as scope is also on 10X. You should check CH1's 10X mode is set correctly. Recall previous instructions where both probe and scope need to be on 10X to get correct readings (so oscilloscope scales them correctly)

AC line trigger uses 50 / 60Hz mains voltage as a reference, it is not useful for this application but has uses in power supply repair etc

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Great.
Zoom a little in on this area...we need to be able to see the cycles more clearly
Then wait for a fault...what do you see? Any obvious change? Could be very minor change.
If it's not so obvious on this one, we may need to look at a larger burst (like the one on the left of the image), as fault may only be present on those ones.

[tom66]

Re: LG 60PZ750 running hot and maldischarged

any update on this? would be interested to see what you discovered.