Hello all, I have this viewsonic VX910 (M#VS10162) that displays normal images to the exception that the top 1/4 of the 19" screen is slightly darker than the rest of the screen. It's not completely dark, you can still see the image. I took the monitor apart to see if any caps were swollen and found none. I noticed besides the main plug to the monitor there are four plugs running to the display. Are these plugs the power source to the back lighting and is there a possibility that one of the four bulbs (I'm assuming there are four bulbs) is out. If not out is there a possibility the power supply is not providing enough power to that bulb. I know there are a multitude of possibility's but I'm just suggesting things that would be things to test and I'm also new to LCD displays. Thanks to anyone who could help.
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Re: Viewsonic VX910 backlighting
Capacitors (C designation on the PCB board) die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.Originally posted by sstipiotis View Post
The plugs provide power to the backlights or ccfls. Most lcd monitors work on an "all or nothing" approach when it comes to the ccfls. That is, either all the ccfls work or none at all. So it is highly UNLIKELY that one ccfl is not working while the other three are working.Are these plugs the power source to the back lighting and is there a possibility that one of the four bulbs (I'm assuming there are four bulbs) is out.--- begin sig file ---
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Re: Viewsonic VX910 backlighting
Yes the 4 plugs are the connectors for the CCFL backlights.
If there is a problem with a CCFL usually you will notice what is referred to as “2 seconds to black”
If there is a problem with one of your ccfls, Depending on how tight the sense circuitry programmed in your monitor there is a possibility that you may NOT GO into 2 seconds to black.
I think the easiest way to see if your inverter is working correctly would be to find a CCFL that is not inside a panel that you can use for testing, and see if each CCFL socket is able to light the CCFL at about the same brightness. You will have to power off and on for each test.Make sure to have all CCFLs hooked to the inverter when you testWhatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!
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Re: Viewsonic VX910 backlighting
Thanks for replying. I'll post some photos of the problem and the two circuit boards. I'm not sure which caps to test for this problem but hopfully the photos I post will help. I can't find any scimatics for this model which would really help. Ill post photos soon. THANKS!!Comment
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Re: Viewsonic VX910 backlighting
Ok here are some pics of the problem. If you set the screen color to white the bar is not present.Attached FilesComment
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Re: Viewsonic VX910 backlighting
IMHO, if it was a lamp, or inverter issue there wouldn't be that sharp a transition.36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....Comment
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Re: Viewsonic VX910 backlighting
I haven't seen this myself so these are all uneducated guesses.Originally posted by sstipiotis View Post
1) One thing you can try is to swap CN1 and CN2 (I can't quite make out the pcb designation so this is a guess) and see if the display changes?
2) The other thing to try is to carefully reseat the black panel cable that goes to the logic board (both sides)? You will have to peel that tape off.
3) And it still could be bad caps? See
https://www.badcaps.net/forum/showthread.php?t=14518
It is the not the same symptoms, but it shows how caps can affect the display.Last edited by retiredcaps; 05-10-2011, 04:01 PM.--- begin sig file ---
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Re: Viewsonic VX910 backlighting
CN1 and CN2 are the two pairs of plugs right? Should I switch the two pairs or each individual plug at each pair. I already unpluged and pluged the main connector to the screen both ends.Comment
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Re: Viewsonic VX910 backlighting
OK, switched the pair no change. Should I start to test all the capacitors at this point?Comment
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Re: Viewsonic VX910 backlighting
If you have an ESR meter, then yes.Originally posted by sstipiotis View Post
A multimeter that measures uF is useful as well. Both are required to ensure a cap is good.--- begin sig file ---
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Re: Viewsonic VX910 backlighting
Thanks so much for the advice. I will start the testing and let you all know if I find something new. THANKS!!Comment
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Re: Viewsonic VX910 backlighting
These boards do cause various problems,in the inverter circuits,and as you seem to have eliminated the CCFLs as the cause, then the other main suspects are the inverter transformers,the secondaries regularly fail, the brown Poly caps next to them,and the four resistors surrounding them,the transistors on the back of the board also regularly fail,but suspect those are not the cause in this instance.
Compare the resistance of the inverter transformers,look closely at the Brown caps and see if one is starting to bulge,and compare resitance of the resistors.Comment
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