Question about Olevia LT37HVS 37 in. LCD HDTV

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237v Power Supply Output

What should the output voltage from the power supply that feeds the backlight inverters be?

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Posted on Sep 21, 2008

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The picture went "dark" but


Hi,

This is an indication that the backlight of your unit is not working properly. This is caused by faulty either in the power supply board or the inverter board. You have to check the output voltage of the power supply board feeding the inverter board, if present replaced the inverter board. If not, check the power supply board for leaky electrolytic capacitor or replaced the entire power supply board.


Hope I helped you.
Have a nice day!
Thanks for using fixya.

Sep 04, 2011 | Toshiba 14VL44G 14 in EDTVReady LCD TV

Tip

Basic LCD Monitors troubleshooting guides


By Bud Martin
First if you can, try the monitor with other PC first to make sure it is not the PC problem.
Notes: We are dealing with high voltage that can kill you! so if you are not sure what you are doing, please have it fixed by the pro that has proper tools and safety equipment. Try to use GFI outlet and isolation transformer when work around the TV set and DO NOT DEFEAT THE GROUND PIN OF THE OUTLET/POWER CORD.

The monitor will have at least 2 circuits boards, one board will be the logic board where the video cable from PC is attached to, the second board used in most monitors today is the Power supply/backlight inverter board combinations. Some monitors will have separate power supply module and backlight inverter board.
The monitor should be connected to the running PC otherwise it will go into standby mode.
The operations of each board:

1) The Power supply board:
It takes the 120vac 60Hz and converts it to high voltage DC (around 160~170vdc filtered by the 80~150uf 250~450vdc cap) by the bridge rectifiers to be used by the switching power supply circuits that converts this DC voltage into high frequency (around 50~100 KHz) AC for driving the step down transformer. The outputs (usually 2 outputs) of the transformer will be rectified by the diodes to produce the regulated 5vdc for the logic board, and regulated 12~20vdc (12vdc is usually for screen up to 17inch, 16~24vdc for 18~24 inch screen).

The power supply circuits are always on (unless the monitor uses the power switch that actually disconnects the power from the outlet which is rarely used these days) which means that it is running 24/7 using the monitor or not, any spikes and surge will be fed into the monitor power supply.

Common problems:
Blown fuses, bad caps (leaking/bulging tops or bottom seals, please note that bad cap may look normal but it can have high ESR (Equivalent Series Resistance). The DC filter cap should be low ESR type for using in the switching power supply; general purpose electrolytic types will not last very long in switching power supply circuits. Poor solder joints, over heated components.

Testing:
Plug the monitor in but do not activate the power switch so the backlight inverter circuits will be off. Check the 5vdc and the 12~24vdc to make sure they are OK. They should be tested with the load, you can use 6V 1A (6watts) lamp for the 5vdc, and car lamps such as 1157 (12v 8watts lo/26watts high) turn signal brake lamp using high filament connection for testing the 12~18vdc (or use two 1157 in series for 19~24vdc) for the backlight inverter circuits.
If the power supplies are working, the output voltages should be steady at the rated voltages. The power supply will go into shut down if it detects too much current draw due to false in the power supply or short circuits in the backlight inverter or in the logic board.

2) The backlight inverter circuits:
It takes the 12~24vdc and converts it to high frequency AC to drive the inverter transformers CCFL (Cold Cathode Fluorescent Lamp) assemblies. The transformers will drive the CCFL by applying the start up voltage (around 1500~2000v), when the CCFL start conducting, the voltage will drop down to about 500~800v.
The inverter has detection circuits to detect open circuit if the lamp is not attached or does not fire up after the start up voltage is applied, it will go into shut down. It will also shut down if the lamps draw too much current due to ages (when lamp gets old it will draw more current).
The inverter gets two signals from the logic board, one is the backlight ON/OFF signal, the other one is the Dimming signal for the lamps.
Common problems:
Bad filter caps, resonant caps (in the inverter output circuits), blown transistors/IC, shorted or open transformer winding.
Testing:
You should have spare lamps for testing the inverter circuits.

3) Logic board:
The logic board get the signals from the VGA (ANALOG) or DVI (DIGITAL) and processes them and feed them to the LCD panel T-CON (Timing Controller) board on the back of the LCD panel.
It also sends out two signals (backlight ON/OFF and Dimming) to the inverter circuits when the monitor is on and getting the signals from the PC.
If the logic board does not get the signal from the PC, it will put monitor into standby mode.
The 5vdc feeding it is converted to 3.3v, 1.8vdc by the switching buck converters to run the processor.
The logic board also sends the 5vd or 12vdc power for the T-CON board, if the voltage is not there, you will see white/grey glowing screen only.
Not much repair you can do on the logic board unless you have the full service manual and surface mount repair station.

4) CCFL and Inverter circuits testing:
If you don not have the inverter and lamp tester boxes you may be able to do a simple test by using these steps:
If the screen flashes on for a second, you can disconnect all the lamp connectors and connect it into one of the transformer output connector and see if you will see the flash on the screen, if you do, then try it with another transformer output connector to see if it also get the flash on the screen.
Repeat the procedure with other 3 lamps. If all the lamps do flash on for seconds then more likely the lamps are OK. If lamp only flash on one of the transformer output then you will know that the problem in that transformer inverter circuits.
If none of the lamps flash at all then the problem is in the inverter circuits, power supply, or not getting the on signal from the logic board.

Bad caps
http://i.fixya.nethttp://i.fixya.nete17e9cc.jpg

Power supply/inverter board (L), Logic bd. (R)
http://i.fixya.nethttp://i.fixya.netbc19983.jpg'

Dead T-CON bd, blown fuse. Get glowing screen only.
http://i.fixya.nethttp://i.fixya.net4fbd9e1.jpg

T-CON board's fuse F101
http://i.fixya.nethttp://i.fixya.net8506e44.jpg

Inverter board surface mounted fuses, F1 and F2

http://i.fixya.nethttp://i.fixya.net1bf6596.jpg
Bad lamps (Blackened ends, burnt /poor soldering)

http://i.fixya.nethttp://i.fixya.net5c8952e.jpg

http://i.fixya.nethttp://i.fixya.net4e5e9a1.jpg

Bad LCD panel (solid vertical lines)

http://i.fixya.nethttp://i.fixya.netffe90fe.jpg

Bad LCD panel due to bad T-CON board
http://i.fixya.nethttp://i.fixya.netef48b18.jpg
Failed TV and Monitors:
http://s807.photobucket.com/albums/yy352/budm
http://en.wikipedia.org/wiki/Capacitor_plague
Make your own test lamps: http://www.badcaps.net/forum/showthread.php?t=19987

on Sep 25, 2010 | Computers & Internet

1 Answer

My TV has sound but the screen is blank, can you help?


Hi pine2349,

This kind of symptoms is an indication that the backlight of your unit is not working.

You have to check the output voltage of the power supply feeding the inverter board. If it is present, you have to replace the inverter board, if not, the power supply is faulty.

Hope I helped you.
Have a nice day!
Thanks for using Fixya.

Aug 26, 2011 | Protron PLTV-37 37 in. LCD Television

1 Answer

The screen went black


Hi elav2,
Power on the unit in the dark room then shine with the flashlight directly inthe screen, you will barely see the images. This is because your backlight isnot functioning. The following reason is the caused.
1. Power supply - missingB+(supply voltage) coming from this board feeding the inverter board. This iscaused by faulty transistor, dried/leaky electrolytic capacitor, open fusibleresistor.
2. Inverter board - eventhe B+ is good from the power supply, if the fuse, driver transistors/IC's, high voltage transformer is faulty no output to the backlight resulting to black picture.
3. Busted backlight - eveninverter board is good but if this is busted resulting to black picture also.
Diagnosing the fault is technical and if you don't have necessary tools and test instrument and can't fix it yourself, I wouldadvice you to look for an experiencedtechnician to isolate theproblem.
Hope I helped you.
Have a nice day!
Thanks for using Fixya.

Aug 05, 2011 | Vizio 42 in. LCD TV

1 Answer

My proview 3200 has picture but no sound


Hi gravdar4,
Power on the unit in the dark room then aim the flashlight directly to the screen, you will barely see the images. This is because your backlight is not functioning. The following reasons are the caused.
1. Power supply- missing B+(supply voltage) coming from this board feeding the inverter board. This was caused by faulty transistor, dried/leaky electrolytic capacitor, open fusible resistor.
2. Inverter board- even the B+ was present from the power supply, if the fuse, driver transistor, driver transformer was faulty, no output to the backlight resulting to black picture.
3. Busted backlight
Diagnosing the fault istechnicaland if you don't have necessarytools and test instrumentand can't fix it yourself, I would advice you to look for anexperienced technicianto isolate the problem.
Hope I helped you.
Have a nice day!
Thanks for using Fixya.


Jun 12, 2011 | Proview PA-32JK1A 32 in. LCD Television

2 Answers

Tv has black screen, no picture


Good day!

Please before we go to the further troubleshooting please to play a DVD or recorded shows to determine if the problem is in your TV or cable connections.

If the problem persist please try to replaced this simple procedure on how to fix that problem.

  1. Remove the back cover of your TV.
  2. Check the 24vdc from the power supply going to inverter board using multimeter tester (range on DC)
  3. If you have 24vdc on the input voltage of inverter board,try to check the output voltage of that board,it should have 500vdc going to the cathode light inside of TV (back light)
  4. If you don't have the 24vdc on the inverter it means your power supply got trouble.
  5. You have better chances if you have failing capacitors on the power supply.Just look the image of capacitor if it is leak/bulged on the top.
If the problem is still there and you have other question just add a comment

I hope this solution will be helpful.Thank you for using FixYa.

May 31, 2011 | Akai LCT2715 27 in. LCD Television

2 Answers

When I turn my TV on there is sound, but, the picture vanishes after a couple of seconds. Why?


The backlight inverter is what powers the screen to "light up." You will need to check your power supply for the proper voltages going to the backlight inverter. If those all check out ok, then you need to replace your inverter to get your image back. You can find a new inverter by searching "inverter + model number of your tv.



Please rate if this helped :)

Apr 04, 2011 | LG Televison & Video

1 Answer

I have sound but no picture on an Olevia 237V


If you get no picture on all inputs (TV, DVD, ETC.) then the problem can be in the backlight inverter board or the power supply that supplys the power to the inverter board.

Nov 01, 2009 | Olevia 237T 37 in. LCD TV

1 Answer

Olevia 237V Backlight problems


Voltages do not dance around and should be constant and within stated parameters.. The board producing those crazy readings is the issue.

Mar 12, 2017 | Olevia LT37HVS 37 in. LCD HDTV

1 Answer

Olevia 237V Backlight problems


Check inverter supply voltage, (should be constant and stable) if found ok, then inverter or back-light tubes are suspected.

Sep 06, 2008 | Olevia LT37HVS 37 in. LCD HDTV

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