TV/monitor turned into a light source?

[reeferman]

Over the years I have done such to cracked screen TVs and dead monitors for extra income. They have been well received and there is a market for them.

TVs and monitors can be used in any number of applications for extra light. Some monitors have been converted to run off 12 volts and used in various mobile/off the grid applications.

Is there somewhere we can post successful "how to do it" conversions and/or seek info by make/model/etc.?

Does something currently on the web or in VK?

Phil

[old_tv_nut]

I think I've skipped past some YouTube videos on this topic.

[reeferman]

I have watched them and they are, technically speaking, non-technical.
The ones I've seen don't take into account that most will go dead after 15 minutes if all they've done is just remove the LCD screen.

[Electronic M]

Here or the off topic section would probably be the most appropriate place to chat about it.

Part of me would like to see it discussed here and see some young whipper snapper as appalled at a flat panel lamp/sign conversion as us tube TV guys get seeing a nice console get gutted by the dogTankLiquors.

[JohnCT]

Originally Posted by reeferman

I have watched them and they are, technically speaking, non-technical.
The ones I've seen don't take into account that most will go dead after 15 minutes if all they've done is just remove the LCD screen.

Correct.

Most TVs shut off with a no signal condition.

There are ways around this, but the methodology is different for just about every model.

Some earlier TVs just used an enable line and an analogue dimmer control line from the main to the power supply board where the LED drive control is *generally* kept.

For these, just tapping the 5V standby over to the enable line with a 100 ohm resistor will turn on the LED supply.

At this point, the LEDs will either turn on dimly, excessively bright, or not at all. With an analogue input, simply building a resister divider network to feed the analogue DIM line some voltage about half the standby voltage will get the LEDs to work and stay on.

Here's the bigger problem. There is a relatively small window between when the LEDs are too dim and when they are too bright and reaching maximum current.

The old CCFL tubes (first LCD TVs) had back light life of about 80K hours, and we changed very few tubes unless the customer never shut them off. When LEDs came out, we figured the back light part of the repair business would end, but what we found out is that LED back lighting schemes have a quarter the life of CCFL tubes, and often a tenth of them.

A good percentage of scrapped TVs will already be suffering one or more LED failures inside the screen. BTW, the LEDs in TVs are mostly the type with an internal zener across the light emitting junction. If a 3 volt (for instance) LED opens, the voltage across the LED goes from 3 volts to whatever the string voltage is, so the zener (hopefully) shorts hard enough to effectively jump out the open LED. Often, the LED partially shorts, the string still runs, bu the partially shorted LED now starts running hot and burns a hole into the LED strip until the strip itself fails.

LEDs are extraordinarily non linear as other diodes are. They draw almost nothing until the voltage hits their conduction target when the current starts ramping up exponentially.

For this reason, the LED power supplies are not voltage regulated, but current regulated. If one is to make a light box out of a LED TV, they MUST make a current measurement of the LED string and design their dimmer circuit to stay well below the rating of the LEDs.

Now, if you have a TV that uses a PWM signal from the main to the LED power board for dimming, a PWM generator drive IC circuit must be built to get the LED power board to work.

Another option is an external universal LED drive board, but the internal wiring of the particular display box must be taken into consideration. There an almost infinite amount of ways the strips inside the screen are wired. They could all be in series, or a combination of series and parallel, or two to twenty individual strings could exist for local dimming models.

Since many scrapped TVs are already mostly used up in the LED department, repurposing them as lights sources may be a waste of time.

If someone has access to brand new TVs damaged during shipping, then these TVs could be used and have a considerable life if the LED drive circuit is modified so they run at lower current than the TV needed.

John

[reeferman]

John,
Thanks for your technical explanation!
Phil