LCD power light is on and green (getting signal from the video card) but the screen is black. I can see my desktop when I shine a light onto it...
I took the monitor apart and nocitced 5 blown capacitors.. This leads me to believe that the backlights may be ok.. but will for sure when the capacitors are replaced.....
I replaced the capacitors and plugged the monitor back in. Immediatly one of the new capacitors popped, smoked and was leaking some stuff.... so Im sure that i need to test some fuses and transistors.. problem is, Im not exaclty sure which is for what and how to test properly.
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Re: LCD Monitor is black... blowing transistors
Bulging or "blown" electrolytic capacitors are a common problem with LCD monitors. If you replaced them with correct parts (voltage rating) then one of two situations comes to mind: 1. Electrolytic caps are polarized, if you install them backwards they will blow quickly. 2. The voltage the circuit provides exceeds the rating of the cap. A 5 volt cap in a 12 volt circuit will blow quickly. The voltage regulation circuit may not be working. Monitor Mike
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Check for blown MOSFET IRFU9024N and transistors C5707/5706, and fuse in the inverter circuits section. Also look for bad caps with bulging top/seal. See some pictures of failed Dell monitors (BenQ made alot of monitors for Dell), http://s807.photobucket.com/home/budm/allalbums
Disconnect the signal cable from CPU and power on.You should get a BenQ Blue screen.
If no Display,Problem is definitely monitor related ie monitor has a hardware defect most probably the power/invertor board has a few blown components.
If you are technically able,you can dismantle monitor and check components on the Invertor board which you may find on my other posts.
Please reply if you need more help.Please rate this solution.
If screen says "Signal cable not connected " all the time till power led switches to Amber chances are monitor is ok and problem is with graphic card or cpu.Connect to Known working CPU and confirm that monitor is the problem.
If same problem persists on another working cpu after changing signal cable,the interface board in the monitor could be defective.
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.
I wonder if this has a backlight in it. Most/or all LCD flatpanel displays use a backlight in them, namely a small florescent tube (a tiny version of the office florescent lights). If this is burn't out, or the little power supply which runs it dead, you will have a black display. The image is actually there, you just can't see it, except perhaps faintly when external light hits it just right.
The display must be disassembled to check this light. If you have tech savvy, and some equipment, voltmeter, maybe an oscilloscope, you could check it out. Where to get a replacement lamp? Google it... perhaps the manufacturer.
We recently come across this problem - and like many others - looked online for a solution without much luck. So it was a clear case of fault finding. The symptoms of the indicator changing from amber to green on signal indicated a problem with the powersupply/inverter board, and not the smaller signals processing board, so that's where we started. On careful testing it soon became clear that the black picofuse (just above the main transformer) was blown. This indicated a major fault in the backlight driver circuit. There are two independant yet identical circuits that drive the backlights - this made testing easy. We found that the two driver transistors marked C5707 were almost completely shorted. You will identify these as being two of four identical black components with a built in heat sink at each end of a grey 0.22 Microfarad capacitor - looking much like bookends! Replacing these C5707 transistors with BD139 transistors (Note: these are constructed mirror image to the original transistors - fit them backwards to the original transistors !) and replacing the 3 Amp picofuse with a 1 ohm 1 watt resistor completely solved the problem ! - Colin Knight, Radtvid Electronics, South Africa.