A friend brought me a 30" benq lcd tv. the problem is this thing powers up, the backlight comes on briefly and then goes out. no matter what input i use - component, vga, dvi, or composite - it will not light. the display is black, the power light is on green and the fan in the back of the unit is spinning. tried using the "i" key on the remote or the input key on the top of the tv - no result. with a dvd player, sat receiver or a pc - nothing works. every time you turn it on the same thing - brief backlit black screen then a totally black screen. any help would be appreciated.
Zippie
p.s. i build computers - so i am comfortable with electronics, just not an expert.
well...i just spent the better part of 2 hours disassembling this monster - it turns out there are 16 flourescent tubes directly behind the lcd itself, with a mass of filters as well. i cant see all 16 going at once - maybe one or two...but not 16. i assume you would come to the same conclusion. so that would leave me at the inverter board or the "on" signal coming from the processor. your thoughts?
Zipwell...i just spent the better part of 2 hours disassembling this monster - it turns out there are 16 flourescent tubes directly behind the lcd itself, with a mass of filters as well. i cant see all 16 going at once - maybe one or two...but not 16. i assume you would come to the same conclusion. so that would leave me at the inverter board or the "on" signal coming from the processor. your thoughts?
Zip
see....now i get more information from the owner - apparently in the last few months he has had to remove the back of the unit to get it to work...woulda been nice if he told me that when he brought it over. I guess i muddle through and see if i can find evidence of overheating and/or burnt connections. some peoples kids i tell ya.see....now i get more information from the owner - apparently in the last few months he has had to remove the back of the unit to get it to work...woulda been nice if he told me that when he brought it over. I guess i muddle through and see if i can find evidence of overheating and/or burnt connections. some peoples kids i tell ya.
yes i am having the exact same problem with my benq lcd tv. when the screen flashes at turn on, if i leave it off for a few minutes, it will light next time and be ok for hours of use.
i will look into an inverter solution.
thanks.yes i am having the exact same problem with my benq lcd tv. when the screen flashes at turn on, if i leave it off for a few minutes, it will light next time and be ok for hours of use.
i will look into an inverter solution. thanks.
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It sounds like the inverter is the issues from what i seen this is a commen problem i have 2 units one for parts.. and this moring my screen started what your were doing .. so i just going to look around for a uses inverter lol
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Re: benq lcd tv
Hi zippie,
Based on your post/description, I am inclined to suspect the backlight which is actually a CCF a small fluorescent tube about 2mm diameter the width of your display either at the very top or bottom of the screen. At times it can also be the inverter circuitry that powers up the said tube. One way is to run your PC and display as if nothing is wrong giving it a minute or soto finished booting everything. If looking closely you will notice semblance of your desktop albeit very faint, very dark or using a flashlight provide illumination to the display at an angle and the display is there, then chances are it is the backlight. Otherwise, it can be the input circuitry. Of course you have to open the monitor up and replace the defective component, More often than not no soldering required. Hope this gives you an idea or two. Lots of luck and pls post again how things turn up. If
Hi again zippie, Ooooppppps, failed to notice the size 30, that would really require a good numbber of CCF (16). In any case, look for colder solder and/or discolored connectors male/female, both to and fro the inverted circuit(s), it is also a good idea to check the wires leading to the CCF themselves. Some brands/model are prone to arcing burnts causing terminal corrosion. Pls remember CCF works high freq, high volt. Past experience CCF connectors more prone to burnt than the inverter. And if it is the inverter, chances are and hopefully that it's just a cold solder which should be very visible. It seems you're in the right track, cheers.Hi again zippie,
Ooooppppps, failed to notice the size 30, that would really require a good numbber of CCF (16). In any case, look for colder solder and/or discolored connectors male/female, both to and fro the inverted circuit(s), it is also a good idea to check the wires leading to the CCF themselves. Some brands/model are prone to arcing burnts causing terminal corrosion. Pls remember CCF works high freq, high volt. Past experience CCF connectors more prone to burnt than the inverter. And if it is the inverter, chances are and hopefully that it's just a cold solder which should be very visible. It seems you're in the right track, cheers.
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Sounds like a backlight problem to me. If you input a signal to the HDMI or Composite input and then it goes black have you tried taking a flashlight to the screen to see if the picture is still there but just dark? That would indicate a backlight issue. That model appears to be an LED edge lit backlight, so if the picture is still there after going black your going to have to trace out the backlight circuit and see whats going on. Usually with LED backlighting if it comes on at all then the LED's are good, its just the driver supply thats failing to keep them on. Some TV's have a small separate board that provides the backlight control, but i suspect with this model its on the power supply board and not the motherboard. Have you checked that board? It could be bad caps on the power supply board, check the voltages to the backlighting when it lights up and then when it goes dark. It could just be some failed capacitors on the power supply causing that voltage rail to drop off.
When you turn on the TV check to see if you even get momentary backlight. Would turn on for a second or two. If it comes on briefly then goes out, you havve a short in your lamps. This would mean bad panel. If it never comes on at all, check your power supply and see if it is putting out 24 volts DC. If not, replace your power supply.
your backlight is out and one of two things can cause this . 1 being the invert board is failing, or you have a couple of bad caps in the power supply. you can see the bad one they look like little cans , the bad one will have puffy tops on them ...if you see them change them or have it done if not them you will need the inverter board serviced or replaced
hello my friend you have some loose connections on the digital board.this board is located right in the top center of the tv.if you do not have repair skills call the repairman he should not charge you too much for this job.
good luck
One of two things, the backlight inverter board is going bad (usually has open winding on the transformers), second, the 24vdc power supply section of the main power supply module is bad due to bad filter capacitors.
Resolder the power transistors on inverter board and also check them.If display is not there at all some of this 4 transistors C5707 should be defective.Check associated fuse and Fet which drives the transistor.
Also check with Benq ,Normally offers three year warranty.
How old are the monitors?
Normally backlights last at least 30,000hrs of working.
Normally problems on Inverter board transistors near yellow inverter transformers.
Samir
hi. i had the same problem and fixed it. the problem are the 4 transistors (C5707) one of more are shorted (Q739,Q740 and Q759, Q760). Also the fuse PF751 (3a) has to be replaced in most cases. In my case i replaced the fuse and 1 transistor (C5707)
well...i just spent the better part of 2 hours disassembling this monster - it turns out there are 16 flourescent tubes directly behind the lcd itself, with a mass of filters as well. i cant see all 16 going at once - maybe one or two...but not 16. i assume you would come to the same conclusion. so that would leave me at the inverter board or the "on" signal coming from the processor. your thoughts?
Zip
see....now i get more information from the owner - apparently in the last few months he has had to remove the back of the unit to get it to work...woulda been nice if he told me that when he brought it over. I guess i muddle through and see if i can find evidence of overheating and/or burnt connections. some peoples kids i tell ya.
yes i am having the exact same problem with my benq lcd tv. when the screen flashes at turn on, if i leave it off for a few minutes, it will light next time and be ok for hours of use.
i will look into an inverter solution.
thanks.
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