TV Repair: some days you are unlucky...

[RayDunzl]

A traditional Telco has thousands of terminals with 50VDC on them, that you will work upon without fear or caution or even noticeable tingle.

Only a few milliamps of current are available there.

However, occasionally a pair of those terminals will provide around 130VAC (also current limited) which will startle you if digging around in the jumpers at that moment, or maybe you have your forearm resting on the block.

The 50V is what "powers" a landline phone's voice circuit and dialing at your house, the 130V rings the bell.

Above, the underside of the block goes to the switching line cards the jumpers on top of the block go to another block exposing the cable pairs that go to your home or office. Those are usually mounted vertically on the backside of the above thing, called the Main Distribution Frame.

 

[Asylum Seeker]

TV? What's that?

 

[Doodski]

TV? What's that?

Television.

 

[mansr]

It's not just voltage, it is current (power) as well... 12 V from a car battery or alternator can be more painful than 20 kV from an old CRT.

What now? Unless you're licking the terminals, 12 V will not produce enough current to be noticed, let alone painful.

 

[mansr]

An traditional Telco has thousands of terminals with 50VDC on them, that you will work upon without fear or caution or even noticeable tingle.

Only a few milliamps of current are available there.

However, occasionally a pair of those terminals will provide around 130VAC (also current limited) which will startle you if digging around in the jumpers at that moment, or maybe you have your forearm resting on the block.

The 50V is what "powers" a landline phone's voice circuit and dialing at your house, the 130V rings the bell.

Phone lines have a fairly high series resistance that limits the current, or the ring voltage would be dangerous rather than merely a tickle.

 

[DonH56]

What now? Unless you're licking the terminals, 12 V will not produce enough current to be noticed, let alone painful.

A welder operates at 10-20 V or so at tens to hundreds of amperes of current. It can hurt. A car battery can deliver tens to hundreds of amps; that much is used when starting or winching (if you have an electric winch). And again it depends upon your contact points, where the current flows...

 

[mansr]

A welder operates at 10-20 V or so at tens to hundreds of amperes of current. It can hurt. A car battery can deliver tens to hundreds of amps; that much is used when starting or winching (if you have an electric winch). And again it depends upon your contact points, where the current flows...

Human skin is not made of metal. The comparison to a welder is invalid. Ohm's law and all that.

I did a quick test just now, connecting a bench supply to my finger using crocodile clips, then turning the voltage (DC) up gradually. At about 30 V, the sensation from the current started overtaking the pinching of the crocodile clips. Casually handling the wires doesn't create anywhere close to that contact pressure, so the voltage has to be much higher to produce a similar sensation.

 

[Alexanderc]

Have you all seen this guy?

He’s got some more on topic videos, but the more recent ones are more entertaining.

 

[DonH56]

Human skin is not made of metal. The comparison to a welder is invalid. Ohm's law and all that.

I did a quick test just now, connecting a bench supply to my finger using crocodile clips, then turning the voltage (DC) up gradually. At about 30 V, the sensation from the current started overtaking the pinching of the crocodile clips. Casually handling the wires doesn't create anywhere close to that contact pressure, so the voltage has to be much higher to produce a similar sensation.

All I can say is what myself and friends have experienced working on our cars. YMMV.

Stay away from the spark-plug wires...

Have you all seen this guy?

He’s got some more on topic videos, but the more recent ones are more entertaining.

Many times. The ones with his wife (or whomever) screaming at him in the background are fairly entertaining...

 

[mansr]

Stay away from the spark-plug wires...

Of course, but that's thousands of volts.

 

[Tks]

It has a couple of interesting features to deal with static content:

1. Detects logos and lowers their luminance.

2. When it detects static video frame, it starts to shift them gradually (about once a second).

Pretty clever signal processing that is possible now, but not a few years ago.

On computer use, I have had an OLED on my main music system driven by a PC for some three years. I don't use it all the time though so no damage. When the new LG puts up help text, you want to cry. It is that sharp and nice!

The frame shift is pure nonsense, per pixel shift isn't enough for logos, as they mostly occupy multi-pixel widths and heights.

Luminescence shifts are silly, and I've not seen this much at all functional in practice with mine. It's not as useless as frameshift, but I'd need to wait for independent long-term testing to see if this approach is of any decent utility in actuality.

 

[amirm]

I keep forgetting to update this thread. After some angst about the hassle they are going to give me to exchange the bad power supply board, I called the company that I bought it from (they would not provide customer service via email). To my pleasant surprise, the person who answered immediately rushed me another board and told me to not worry at all about returning the bad one. The new board arrived in two days and worked like a charm.

Alas, something must have happened to the backlight after sitting on its face for two weeks and now they are blooming rather bad. "Worse yet," by then I was so spoiled by watching our LG TV with its absolute blacks that there was no going back. So we retired the Samsung to the guess room and that was that.

So if you need these boards in the future, don't be afraid to buy them. For just $50 plus shipping for a board that far more than that in parts, it is a very good way to go if you can accept the risk of getting a bad used board.

 

[amirm]

Luminescence shifts are silly, and I've not seen this much at all functional in practice with mine.

On mine it absolutely works to lower the luminance on logos as you step through the three steps.

 

[amirm]

The frame shift is pure nonsense, per pixel shift isn't enough for logos, as they mostly occupy multi-pixel widths and heights.

That is not for logos but entire frame for when you have static content for the whole image.

 

[Sal1950]

What now? Unless you're licking the terminals, 12 V will not produce enough current to be noticed, let alone painful.

Well strange things do happen. We were hanging out in the garage way back in the 60s while by buddy Fred was changing the starter on his car. He somehow accidentally got his wedding ring in position to short the main + cable to ground. The ring turned bright red instantly and welded itself in position for a second or two. Burned his finger right down to the bone and the doc's at the hospital had to do surgery on it a couple times to save the finger, but it never was right again.

 

[Doodski]

Well strange things do happen. We were hanging out in the garage way back in the 60s while by buddy Fred was changing the starter on his car. He somehow accidentally got his wedding ring in position to short the main + cable to ground. The ring turned bright red instantly and welded itself in position for a second or two. Burned his finger right down to the bone and the doc's at the hospital had to do surgery on it a couple times to save the finger, but it never was right again.

When I was a car audio installer around age 16-17 I had a very rushed-hurried customer. He asked if there was anything he could do installing his car stereo so he could make dinner at the lake that night. So I said sure how about while I work at the back you work at the front running the heavy red wire back to the rear trunk. About 35 minutes later I heard him yowling in pain and agony. He had connected the red wire to the battery and proceeded to run the wire through the firewall and stuff. He had a snag so he returned to the engine bay and pulled hard and shorted the power cable to ground and the cable was wrapped around his hands. He was crying the blues big time... So anyway he made it to the lake or left in time enough to make it and he got a new power cable for free.

 

[RayDunzl]

Burned his finger right down to the bone and the doc's at the hospital had to do surgery on it a couple times to save the finger, but it never was right again.

Friend of mine was on a stepladder (he was a maintenance man) and somehow caught his ring while grabbing something as he fell off the ladder (I don't know the details).

They sewed his hand to his chest for a month or two, to keep the pieces alive, then got most of it put back together later.

 

[Tks]

That is not for logos but entire frame for when you have static content for the whole image.

But that doesn't make sense even in theory. How would a few pixels of left/right/up/down of a logo that spans perhaps 15% of the screen fix the entire logo section?

What you're basically saying is, OLED is ready for prime time with desktop use.

Many indications point to the contrary

I suppose if you change your TV every 4 years or something, you should be good.

 

[Sal1950]

I know I said this before in this thread but I will repeat,
No way in hell I'd spend big money on a OLED that's still capable of burn-in screen damage.
I had a very expensive rear projection set get ruined IMO by burn-in to the lower right corporate logo corner.
I don't think it was much more than a year old when I started to notice it and it made me sick after spending all that money.
At the time I wasn't even aware of the possibility until I started looking for answers for my ruined TV.
Never again, I can live with the minor weaknesses of regular LCD-LED sets and not have to worry over burn-in.
My next set will probably be a Samsung QLED
https://news.samsung.com/global/how-samsungs-qled-tv-earned-video-magazines-burn-in-certification

 

[amirm]

But that doesn't make sense even in theory. How would a few pixels of left/right/up/down of a logo that spans perhaps 15% of the screen fix the entire logo section?

This is a different feature and has nothing to do with the logo protection. It is designed to reduce the impact of static images like the program guide or paused DVR picture. In these cases pixel shift will definitely change the drive level (think of text over black).