please post test methods you use
thanks!
thanks!
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Re: how to test lcd led backlight?
Jump with a low ohm resitor between ps-on and 5v stby, and 5vstby and bl-on (inverter on off) -
Re: how to test lcd led backlight?
OK, are you asking how to test individual LED mounted on the circuit board that form LED string?
You can use 3V battery with 100 Ohms resistor to limit the current for testing individual LED.
Or you already verify that the LED driver circuits are OK but the LED still does not light up?
Test LED string current draw using DCA.
https://www.badcaps.net/forum/showpo...4&postcount=95
Or used indicator:
https://www.badcaps.net/forum/showpo...&postcount=107Last edited by budm; 03-27-2015, 11:55 AM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: how to test lcd led backlight?
Yes, something like an adjustable voltage source with constant currentComment
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Re: how to test lcd led backlight?
his would be a constant current source would be the voltage regulator.
What do you think?Comment
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Re: how to test lcd led backlight?
That will be correct if all the LED int he string are good, but if one goes open circuit then nothing will happen, but you need to know how many LEDs are in the string to determine what the power supply voltage needs to be, some string you will need more than 100VDC, Vf of each LED is between 3~3.6V.Last edited by budm; 03-27-2015, 12:36 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: how to test lcd led backlight?
Please, if not asking too much to draw scheme Led string indicator to find out which string is dead.Last edited by pnv; 03-27-2015, 12:27 PM.Comment
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Re: how to test lcd led backlight?
LED's are wired like christmas-tree lights....
One dead--all out.
You just have to test each one in turn. No schematics, just a meter.....TELEFIX
How PLASMA SCREENS WORK, X-SUS and Y-SUS what they do--
http://www.irf.com/technical-info/appnotes/an-1088.pdf
PLEASE DO NOT EMAIL ME PRIVATELY FOR REPAIR ADVICE. QUESTIONS BELONG ON THE FORUM!Comment
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Re: how to test lcd led backlight?
I think it is exciting and dynamic method of insertion of an indicator Lord budmLast edited by pnv; 03-27-2015, 12:48 PM.Comment
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Re: how to test lcd led backlight?
It would be nice if these led strings had standards for each size of screen then one could build a test circuit just to plug in and see if the individual strings worked or not, but that would be to easy.Comment
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Re: how to test lcd led backlight?
See picture, the diodes will get hot so do not run it too long.Attached Filesif you find these attachements useful please consider making a small donation to the site
Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: how to test lcd led backlight?
Bud M don't laugh at me, but I was hoping to unplug all the LED strings and plug them into a separate power source that would eliminate any feed back circuit from turning the the LED driver chip off.Comment
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Re: how to test lcd led backlight?
If you want to use external constant current power source to drive the LED string then the strings are no longer connected to the LED driver board) so there is need to have any power to the TV at all since you are just testing LEDs.
The harder part is to figure out how the strings are connected together and which wire is the Anode and which wire is the Cathode if the panel is not open up to see the LED string, or you can trace the connector on the driver board to see how it is done.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: how to test lcd led backlight?
Yes that is where standards would work.Comment
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Re: how to test lcd led backlight?
? Auto-recovery LED screen ? Resettable Fuse ? Auto-bypass LED?
ST has LBP01 part can bypass any defected LEDs
Benefits
■ Keep LED strings on in case of LED open mode failure
■ Reduced maintenance cost
■ Increase lifetime of the lighting system
https://cdn.badcaps-static.com/pdfs/...34696944c0.pdf
But, new LED TV used 2000 LEDs to make more brighter LED screen. I predict ( Auto-bypass LEDs will be use to build Auto recovery LED screen) in the future !
(I mean, LED will build in bypass circuit in the chip which just two more diodes. )
Tips: So next time don't put a cooper wire cross the defect LED put a diode.This allows the right amount current to flow through the other LEDs.Last edited by Peter Chiu; 03-28-2015, 12:39 PM.Comment
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Re: how to test lcd led backlight?
Constant Current Driver for LED Backlights Tester
https://cdn.badcaps-static.com/pdfs/...eeae3f24ee.pdfComment
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Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.Comment
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Re: how to test lcd led backlight?
LED is a diode too, when manufacture do the masking, it wont cost them not too much to do it.
Basically just a P-N junction.Attached Filesif you find these attachements useful please consider making a small donation to the site
Last edited by Peter Chiu; 03-28-2015, 02:38 PM.Comment
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Re: how to test lcd led backlight?
Not as simple as that. Introduces yield issues, LEDs are made from different types of semiconductor (GaAs is quite common), GaAs doesn't make good transistors.
One possible solution would be a zener diode across the LED, the zener would conduct, heat up then anti-fuse shorted if the LED went open.Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.Comment
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I have a TCL 43S435 with no backlights. I contacted ShopJimmy and they said power supply. I got replacement power supply, but still doesnt work. I have confirmed that there is an image with flashlight test. I have also verified that the led strips work when I probe them with LED tester. Any ideas would be helpful. I am also geting a double blink on the status led when trying to turn it on......Nothing on the power supply looks suspect, and caps look ok. Where should I start to test......Thanks!...
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Vizio e601i-A3 - Has Sound and Display, But No Backlight - Bad Power Supply Board or Bad LED Bulbs ?I was given this TV from my great uncle. He said it just wouldn't turn on one day out of nowhere, replaced the TV, and gave it to me to possibly fix and use for myself.
Upon bringing it home and plugging it up, it showed a standby light.
I powered it on and without a flashlight, the display showed the "V" but the lighting is very dim, but visible.
The screen seems to blackout and stay black, but with a flashlight I can see the display.
With my Playstation 4 connected via HDMI, and running a game I can hear sound.
Assuming... -
I bought this p2210f dell monitor to fix. Schematic is the same as p2210.
Behaviour is that monitors comes on but then backlight switches off almost instantly. If I look with flashlight I can still find the "No signal message". So definitely a backlight issue. Trying to advance the issue I proved that the protection circuit is switching off the backlight by shorting out C3 and resistor to disable the INL chip then re enable by removing the short.
This is where it gets interesting. When I disassembled the monitor to solder leads on c3 capacitor I noticed the backlight flickered... -
Hello all,
Am trying to figure out this backlight issue with this A1990 Macbook Pro.
Tests performed:
There is no backlight even with a good screen.
Backlight IC is receiving the correct support voltages.
Fuse F8400 ok
Current sense resistor R8400 ok
Backlight IC is receiving 3.3V on enable pin.
Backlight IC receiving voltage from PPBUS_G3H, aprox 12.5V.
Backlight IC receiving 5V from PP5V_G3S
Backlight IC BKLT_SCL and BKLT_SDA both measure 0.545V diode mode to ground
I2C_BKLT_SCL and I2C_BKLT_SDA both measure... -
Hey guys!!
I’ve got a question here!
I have a MacBook Pro A1706 that needs the backlight cable replacement — the well-known issue — but the problem is that the code on my original cable is 821-00571-A, and the one I have on hand to install is 821-01229-A.
Well, I asked ChatGPT about it, and the guy told me they’re not compatible and it could even burn the backlight circuit!!
Here’s what the bot told me:
I said to him: “I’m going to install the 821-01229-A.”
ChatGPT replied:Understood — but before you solder or install the 821-01229-A,...11-11-2025, 03:26 PM
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