Antique LED tester II

[capwizard]

llonen said : ( 01-16-2019 )

I got interested in the whole LED Backlight Tester gig some time ago with the view that it might speed up testing of said back lights, and came across a cheap example of the SID GJ2C I think I paid around £10.00 via Ebay. What I found along with others that have tried these is they don't really develop sufficient drive to adequately test the LED panel, kind of a good thing really as they can produce upwards to 300 volts across the probes and to me that is a potential safety issue.

Overall findings then, having one is better than not having one, although they give very mixed results with bad led's often passing, I mean see what others say but I have mostly gone back to my old testing methodology. A variable high voltage supply (upto 60 volts) with current sense set) I can usually test one or more complete strips with this at varying loads.

Hope this helps
------------------------------------------------------------------
This gives me an inspiration, I have been thinking how to accomplish this variable high voltage supply about a month. All I have to do is find a high voltage Insulated transformer. Finally, I found one transformer in the old instrument. (Heathkit CRT Rejuvenator)

to be continued.....

[capwizard]

Re: Antique LED tester II

Would anybody be so kind as to let me know what is the spec. of this Transformer? 54-906

[budm]

Re: Antique LED tester II

Do you know where it comes off from?
Since you have VARIAC, you can apply Voltage to one winding and see what you have on other winding, just apply enough Voltage to get the reading.

[capwizard]

Re: Antique LED tester II

1,2,3)from Heathkit CRT Rejuvenator.

Apple 1/10 th of your line ac voltage, my case is 110v (US)/10 =11v AC
EX: highest voltage is 38v, it means 380 AC if apple 110v.

Rejuvenating a TV CRT, Using high voltage electricity of opposite polarity, I have done approximately 1000 sets. It’s fun to watch when the sparks jump inside the CRT Vacuum tube .

A Basic Rejuvenation with B&K 467 how you can Restore a Weak Tube.
https://www.youtube.com/watch?v=Vw7nmuGdDs0

Rejuvenating
https://www.youtube.com/watch?v=Lv4FIqqGLwg

[capwizard]

Re: Antique LED tester II

Now I want to prove that llonen's theory, old testing methodology is correct.

Will your LED tester deceive you? Let's see it.

1)When I'd have llonen ideals and budm suggestions, The prototype of the this product came out. i found out it was unexpectedly the most powerful LED tester in the world. voltage up to DC 582.4v picture 13)

2)Current limiting uses LR8K4 and it is switchable.

3) At a common LED tester. 4 leds light up. up to 43mA still 4 leds light up

4) at 106mA has 5 leds light up

5) at 156mA has 5 leds light up

6) at 203mA has 6 leds light up

7) at 340mA has 6 leds light up

8) at 445mA has 6 leds light up

9) at 577mA has 6 leds light up, color temperature changed to light blue

10) at 660mA has 6 leds light up, color temperature changed to light blue

11) at 825mA has 6 leds light up, color temperature changed to light blue

12) Wait....Wait...Wait.. a minute, please wait.....I dare not continue to adjust it up to 1000mA.....I know that I am a coward...I am a chicken....I think my wife has no problem to do it ........i will ask her a favor.........

to be continued.....


.

[capwizard]

Re: Antique LED tester II

The unregulated testing voltage from 12.8v 4 LEDs lights up to 17.7 volts 6 LEDs lights up. My question is.... two defects LEDs at a low voltage are not working why work at higher voltage is because like me getting older?

[budm]

Re: Antique LED tester II

Are you monitoring the current when you are doing this?
What are the Vf of the two defect LED's?

[gabiz_ro]

Re: Antique LED tester II

How you use LR8K4 at high current?
Datasheets say have output current limiting and also max is
30 mA at Vin-Vout=12V and temp<85°
0.5 mA at Vin-Vout=450V and temp>125°

In photo looks like TO-92

[capwizard]

Re: Antique LED tester II

it is LR8K4 To-252-3 package.

...use LR8K4 at high current?
Picture 1) I did not because LR8K4 maximum current limit is 20mA, I installed an on-off switch to bypass it.

2,3) I used lr8k4 to do the voltage and current source cc cv experiment.

-------------------------------------------------------------
LR8K4-G - Linear Voltage Regulator, Adjustable, 1.2V to 440V/20 mA out, TO-252AA-3

a wide operating input voltage range of 13.2 to 450V. The output voltage can be adjusted from 1.2 to 440V provided that the input voltage is at least 12V greater than the output voltage.

OUT and ADJ pins to a nominal value of 1.2V. The output current limit is typical 20mA

[capwizard]

Re: Antique LED tester II

These circuits are very simple because I like my life not to be so complicated and I love this LED tester because you have a feeling of weight when you turn the knob.

Many people asked me: what is that? I am very proud to say: this is my Antique LED tester.

Of course, I can use traditional analog meters. Let it has a more antique, nostalgia, and classical feeling. But.. but...but look picture

[capwizard]

Re: Antique LED tester II

Are you monitoring the current when you are doing this?
What is the Vf of the two defect LED's?

I'm sorry, budm. When I finished the experiment I knew the result was when I put current up to 1,000mA One of LED opened then I was ready to clean up my LEDs assets. Picture 1,2

I often found this situation, I will pay attention to it, next time.
LED panel under 10mA, let's say, 20 leds not work but when I put 150mA on it, maybe 15 leds not work. I started to notice that this phenomenon happened.

[capwizard]

Re: Antique LED tester II

Antique LED tester tested on LG 50 whole panel.

1)tested on 10ma

2) tested on100ma

3) tested on 150ma

[capwizard]

Re: Antique LED tester II

Antique LED tester tested on LG 50 whole panel.

1)tested on 200ma

2) tested on 250ma

3) tested on 300ma

[budm]

Re: Antique LED tester II

Good one, I would at least cover that VARIAC rotor disk which the brush is attached to which is at line Voltage just in case you drop something electrical conductive on the VARIAC.
So is the output is isolated now with that black transformer?

[capwizard]

Re: Antique LED tester II

Yes, sir. It is an isolated transformer.

This is a prototype, I do have a case to put it in. Thank you.

[capwizard]

Re: Antique LED tester II

LED panel relationship between current and voltage (collected from #12 and #13) values are like this:

100ma 264.6v
150ma 279.4v
200ma 287.5v
250ma 287.5v
300ma 294.7v
350ma 302.0v

pictre 1) We can prove that LED panel's current and voltage are proportional and textbooks didn't deceive us.

[eccerr0r]

Re: Antique LED tester II

Or did they? (diode i-v)

[capwizard]

Re: Antique LED tester II

The “Light Emitting Diode” or LED as it is more commonly called, is basically just a specialised type of diode as they have very similar electrical characteristics to a PN junction diode. This means that an LED will pass current in its forward direction but block the flow of current in the reverse direction.

LED is nonlinear

light output is essentially proportional to the current in the device (not the voltage) the circuitry around the LED should control current very precisely. A resistor in series with the LED is typically used. The two together, LED + resistor, create a nearly linear IV characteristic

[budm]

Re: Antique LED tester II

Vf of LED is not linear, the Vdrops on the resistor is linear.

[eccerr0r]

Re: Antique LED tester II

A resistor in series with the LED is typically used. The two together, LED + resistor, create a nearly linear IV characteristic

wait...are you even using a resistor for lighting your LED with your variac, I thought you were connecting them directly...

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