LG 50PS60 Sound but no picture Ysus board EBR6183001

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

I think so but Oscilloscopes are new to me. Yes the probe is on 10x and believe I have the Volts/div set to10. The dial is on 2 and the middle knob is pulled out for X5 mag ?? And yes both Cal are all the way clock wise until clicked off.

Are you sure your probe is set to 10X? As the waveform does not look correct for a 10V/div setting. It is way too large - should only be filling around four squares vertically on the display. Also, check the CAL dial for the respective channel is locked in the CAL position.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Ah, that's the issue.
Put the x5 mag back in, disable it. Set to 5V/div.
5V/div is still enough to see the waveform, but we might need to move it up and down.

X5 mag on a scope is not the same as, e.g. 5X on a probe.
It's confusing, but what 10X on a scope probe means is 10:1 ratio, so the signal is a tenth of what it would normally be.
This means that if you have a 5V/div range on your scope, a 10X probe makes it 50V/div.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Got it. just a question should channel 1 and channel 2 read the same when independently scanning or taking readings if all settings are the same. This s a new picture with 5v/div and probe on 10x, does this look better ?

Ah, that's the issue.
Put the x5 mag back in, disable it. Set to 5V/div.
5V/div is still enough to see the waveform, but we might need to move it up and down.

X5 mag on a scope is not the same as, e.g. 5X on a probe.
It's confusing, but what 10X on a scope probe means is 10:1 ratio, so the signal is a tenth of what it would normally be.
This means that if you have a 5V/div range on your scope, a 10X probe makes it 50V/div.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Now I am getting this.

[mmartell]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Looks like Arabic. Maybe tom speaks that language.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

I don't know what to make of pic above but second pic is ok. That is what I expect to see. What timebase is that at?
This'll take some time as we're trying to do it remotely!

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

1ms/div. Below is exactly how I have the scope setup and I have attached a picture of the reading.

time/div 1ms
slope +
coupling AC
source ch2
sweep auto
Level knobs in middle position
Chanel 1 DC
Chanel 1 volts/div 5
vert mode ch1
Chanel 2 DC
Chanel 2 Volts/div 5

I don't know what to make of pic above but second pic is ok. That is what I expect to see. What timebase is that at?
This'll take some time as we're trying to do it remotely!

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Something still not right with that image. Is 5X mode off on the scope, and 10X on the probe enabled? That is a swing of over 500V!! Not correct at all, no way your board would be doing that.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

I believe there is a problem on channel 1, because when I test it with a 9v battery with the probe 1x and just 5v/div it shows no movement but when I do it on channel 2 I get movement of almost two divisions. And yes the 5X mode was off. Thanks for your patience I will report back soon. Thx

Something still not right with that image. Is 5X mode off on the scope, and 10X on the probe enabled? That is a swing of over 500V!! Not correct at all, no way your board would be doing that.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

If you need to check the scope display, try using the calibration point on the front of the instrument. Generally it outputs a 1kHz waveform at 1V or 2Vp-p, will be written on the instrument or in the manual. It can be used to verify the scope is working.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Channel 1 and 2 test, pic's below. The test pin is 2v and set at 5v/div

If you need to check the scope display, try using the calibration point on the front of the instrument. Generally it outputs a 1kHz waveform at 1V or 2Vp-p, will be written on the instrument or in the manual. It can be used to verify the scope is working.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Something definitely wrong with CH1 there as that should look the same as CH2 (which appears correct)
I'd check the AC coupling switch is ok, might need a clean (consider using isopropyl or contact cleaner in small quantities)
Failing that, should be possible to do the tests for now using CH2, with CH1 as your VS_DA trigger.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Sprayed contact cleaner on the AC coupling switch contacts and both V/div switches and let sit for a couple hours to ensure all residue has evaporated.
I say this loosely....... it appears the scope is working correctly now.
I am getting good readings on the 2v test tab so when it is on 2v/div the scope moves up one division. I also tested the scope on 125v A/C with my probe on 10x and the scale on 5v/div but it it peaking at 3 1/2 divisions when I think it should only be peaking at 2 1/2 with my math. Is this normal with A/C current on a oscilloscope ? See pic's below.

Something definitely wrong with CH1 there as that should look the same as CH2 (which appears correct)
I'd check the AC coupling switch is ok, might need a clean (consider using isopropyl or contact cleaner in small quantities)
Failing that, should be possible to do the tests for now using CH2, with CH1 as your VS_DA trigger.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Sprayed contact cleaner on the AC coupling switch contacts and both V/div switches and let sit for a couple hours to ensure all residue has evaporated.
I say this loosely....... it appears the scope is working correctly now.
I am getting good readings on the 2v test tab so when it is on 2v/div the scope moves up one division. I also tested the scope on 125v A/C with my probe on 10x and the scale on 5v/div but it it peaking at 3 1/2 divisions when I think it should only be peaking at 2 1/2 with my math. Is this normal with A/C current on a oscilloscope ? See pic's below.

Be super careful when using a scope for mains. Never connect the earth to anything if you do this and be aware of the electric shock hazard.

120V AC has a peak to peak of 340V roughly. This means the sine peaks at 170V and -170V. So your scope is correct. This may seem odd, but consider that 120V is only an average voltage, representative of the average power that the waveform can produce in a heating element. This is described as root-mean square voltage. So your mains is 120V RMS, which means that if you put the 120V RMS across a heating element, it would produce the same heat as putting 120V DC across it. This is despite the waveform exceeding 120V in parts, as it is only an average. Root mean square is used because if you were just to take a DC average it would come out to zero. Anyone who has touched mains voltage will tell you it very much is *not* zero power!

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Thanks for the word of caution. I do have a health respect for electricity, I work with high current 600V 3ph daily. This is what I am getting now, if this is no good I guess its time to buy another scope. I purchased it from an electronics guy and he guaranteed me it works well and it was calibrated. Any chance I may have messed it up having it on the wrong scale at the beginning ?

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

That looks a lot better.
You'll want to adjust the vertical position so that the whole waveform is visible, and also check your trigger setting for VS_DA, because that looks a little unstable.
We are doing this so we can inspect the start of the waveform to see if the ramp waveform is correct.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Oh, and in answer to your question about messing up your scope, it's pretty hard to do that. They're fairly tolerant towards it.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

That's great !! I adjusted the vertical position to fit the whole wave in the screen, Just to recap my trigger setting should be

Source channel 2
Slope Positive
Coupling AC
Trigger level center position

Also should I keep the same settings for ch2 of 5v/div and 10x on the probe when i hook up to VS DA.

That looks a lot better.
You'll want to adjust the vertical position so that the whole waveform is visible, and also check your trigger setting for VS_DA, because that looks a little unstable.
We are doing this so we can inspect the start of the waveform to see if the ramp waveform is correct.

[tom66]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

Maybe you can send me a video of your scope screen so I can see that it's stable and triggering well, because that still looks a little odd.

[goldbird78]

Re: LG 50PS60 Sound but no picture Ysus board EBR6183001

There is definitely a problem with channel one v/div switch because if I apply a bit of pressure or jiggle it the right way I can get proper test readings. I am assuming it may need a better cleaning but of course the switch is buried in the middle and hard to access. The link below is from chanel 2. I slowly moved the position up and down so you can see the full wave.

Is it possible that the reading dont look right because of a bad signal and that is why the Y board is not working properly ?

https://www.youtube.com/watch?v=Ee9Qh5gRXPo