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Viewsonic monitor comes on for a second, the goes black

This is a discussion on Viewsonic monitor comes on for a second, the goes black within the Other Hardware Support forums, part of the Tech Support Forum category. Hi, I have a Viewsonic VA902b monitor, that only comes on for a second or two, then goes black. If


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Old 06-04-2011, 09:12 AM   #1
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Hi,
I have a Viewsonic VA902b monitor, that only comes on for a second or two, then goes black. If I leave the computer on for a few minutes, and turn the monitor off, then on, it will stay on.
Any ideas what might be causing this?
Thanks,
..... john

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Old 06-04-2011, 10:55 AM   #2
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see if it is the same on another computer

what are you running
video card
cpu
m/board
ram
power supply
brand
model
wattage

check the listings in the bios for voltages and temperatures and post them

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Old 06-05-2011, 03:41 PM   #3
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Hi Dai,
I've tried it on 3 computers now, and it does the same thing on them all. Only once did it stay on for a long period. (I have not been able to repeat that phenomenon.)
video card ..... Radeon 7200.
cpu ...... Pentium 4A 2.4 gig... Northwood.
motherboard ...... Asus p4s8x
Ram ...... 1.3 gig.... three sticks.... Micron Tech, Samsung, and Hyundai....... all pc2100..... 133mhz.... DDR SDRAM
Power supply ....... Deer DR-B450E, max 422 watts
Brand? of computer? no brand.
Model of computer.... no model
Wattage of power supply?
Bios listings
Voltages
vcore voltage ........ 1.61
+3.3v voltage ....... 3.21
+5v voltage .......... 5.10
+12v voltage ........ 12.10
Temperatures
Motherboard ... 34.5°C
CPU ................ 50°C
Thanks,
... john
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Old 06-05-2011, 08:23 PM   #4
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if it is the same on other computers,the cheapest is probably to replace the monitor
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Old 06-06-2011, 05:36 AM   #5
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Hi Dai,
I'd like to repair it. Any ideas what it might be?
Thanks,
..... john
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Old 06-06-2011, 09:54 AM   #6
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i have asked someone with expertise in that area to have a look
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Old 06-06-2011, 11:17 AM   #7
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It could well be that you have one or more faulty capacitors in the power supply.
The power supplies are switch mode and the "condition" is checked using capacitors. If you know how to use a soldering iron and are used to working with potentially lethal voltages you could open it up and take a look .. otherwise take it to someone with experience of these things ..

I'm not joking about the voltages concerned ..

if by any chance this is a flatscreen then the most likely reason is electrolytic capacitors if its a CRT it could be capacitors and it could be bad joints that have weakened due to constant heating cooling processes.

can't warn you enough about the dangers of opening up electrical equipment .. have had more than enough high voltage shocks to keep me on my toes ..
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Old 06-07-2011, 01:33 PM   #8
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Hi Done,
I'd like to take a crack at it, with your help. I appreciate your warnings wrt voltage dangers. I don't much care for shocks either, especially the ones that can stop my heart.
Yes... it is a flat screen. My first thought was to open it and resolder whatever might be the problem. Failing that I would like to replace whatever units are probable problems, and see if that works.
But my first concerns are getting the damn thing open, and guarding against electrocution.
What are your thoughts?
Thanks,
..... john
P.S. I have download the manual, and a picture showing what is where on the board.
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Old 06-08-2011, 08:10 AM   #9
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I'd start by removing the power leads, opening it up and doing a visual check of the boards looking for domed electrolytic capacitors. They are normally the source of loss of backlight and make it look like the set has turned off.

you'll have to find the power supply board, which is the first place to start looking, and carefully note what capacitors look stressed or domed, maybe even leaking. carefully note the values and quantities you need, most likely won't be all the same value or the same voltage. Always use high temperature good quality capacitors and if the store you purchase from doesn't have the value / voltage you are looking for then get the next highest value. never go lower .. either in value or voltage. High temperature means that they are rated at 105 degrees and not the old standard 85 degrees. Low ESR is also a good idea if someone has something available. Means that the capacitor has a low internal impedance which is good when dealing with ripple currents on the supply lines.

these capacitors are polarised so you MUST remember which way round the old one was fitted. Capacitors normally have the negative side marked with a long bar on the sleeving and most boards have the negative side marked up too BUT I have seen recently many occasions ( mainly from one manufacturer) to mark the positive on the printed circuit board making it confusing unless you noted from the start what side goes where.
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Old 06-09-2011, 08:55 AM   #10
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Hi Done_Fishin,
Thanks again for your help. At this point I'm simply trying to open the case without damaging it. I have removed the base, which has allowed me to spread the case at the bottom. I have applied considerable force in an attempt to separte it at the sides, but am afraid of breaking it. There are four holes in the back of the case, which appear to have metal sleeves, but do not appear to be screws. Is there something I'm missing here? I realize that you may not have experience with this specif unit, and may not know how the case is attached.
Thanks,
..... john
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Old 06-09-2011, 09:52 AM   #11
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most of these units have an extra 4 screws fitted where the wall panel would be fitted holding the plastic casing to the metal inner casing .. yours may or may not have these .. they are independent of the base screws

sometimes there are screws hidden behind rubber seals ..

when you are happy that there are no possible screws holding the casing together you should start to pry open the front / rear halves of the casing starting at the bottom of the monitor. I always start there because if any damage does occur trying to get between the cracks in the plastic halves then hopefulyy it won't be noticeable when it is put back together.

use a thin bladed flat screwdriver (I usually use my finger or thumb nails) to get an idea of what direction which half goes into the other. Once you have gained access and opened a small amount of space to work with move the screwdriver along the edging to where you feel that the halves are clipped together applying just enough pressure to break the grip of the clips holding the halves together.

Another thing I read which might help (applies to laptops mainly and seems to work on them) is to carefully grasp the plastic at the edge of the "window" to the display, pulling it outwards and away from the display surface..

the 2 halves are snap fitted and clip together at various parts along each edge, one clipping into the other .. just go carefully and find the individual places that clip together and pry them gently open .. I usually use an inward upward/downward lever action but I have had several years practice to perfect my technique .. some monitors though do tend to be far worse that others and cracks in the plastic might be unavoidable .. go carefully so you don't turn the crack into a complete break ..

Good luck .. and holla if you need any more advice
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Old 06-09-2011, 09:54 AM   #12
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this might give you an idea

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Old 06-13-2011, 04:48 PM   #13
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Hi D_F,
OK....... I followed your advice, and ........ it came apart ..... with some serious force, but no damage..... so..... so far so good. (I wood chisel is a wonderful prying device.http://www.techsupportforum.com/images/smilies/wave.gif) Now..... there are three boards in this thing....one is a printed circuit. I'm sending you pictures of the others, two of the large one (a), which I suspect is the one you'll be interested in, and one of the smaller. Anything jump out at you?



Thanks,
....... john
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Old 06-14-2011, 02:30 AM   #14
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Jump ???? It's knocked me down already .. those capacitors should ALL be flat topped and there are two on your power supply board that have a serious headache ..

1000uF/25V is the first (middle picture next to the two transistors on the heatsink) and there is another one 220uF/25V (middle pic again) near the backlight transformer on the right hand side.
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Old 06-15-2011, 07:10 AM   #15
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Hi D_F,
Should I replace all the capacitors, or start with these two? I have no idea how to repace these. Do I simply melt the solder on the other side of the board? Is there a special technique here?
Thanks,
..... john
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Old 06-15-2011, 11:13 PM   #16
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soldering Iron, Solder, Desoldering wick or Desoldering Pump & wire cutters are required.

Start with just those two, NOTE POLARITY .. these devices are polarised and will possibly explode if mounted in reverse and voltage applied!! The line down the side of the capacitor denotes the negative side of the circuit .. as you remove it note if the board is marked in some way to indicate which side goes where or mark the board with a marker pen yourself!

The capacitors are high working temperature (105 degrees Celsius as against 85 degree Celsius). Replace with same type. Preferably from a well known manufacturer like Panasonic

apply a small amount of fresh solder to joints on reverse of board before trying to suck the old solder away. In the worst case apply heat to joint then manipulate capacitor (joggle it from side to side) so that capacitor leads leave the holes.

The longer lead of the new capacitors is the POSITIVE side, so that lead goes into the hole first. It's easier when the holes are cleared of solder. Apply fresh solder to the leads and holes then cut off the excess lead about 2mm above the board. That's about the height of all the other cut of leads on the board.Excess lead length may cause shorts via the chassis causing other problems.


If in doubt at all, buy the components, take the board and components to a technician and pay him to do the change for you.

If you feel like doing it, change all capacitors now however normally (but NOT ALWAYS ) it's the domed ones that cause the problems
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Old 06-16-2011, 05:33 AM   #17
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Thanks D_F,
You're obviously used to instructing newbies on how to replace capacitors. I'll try the two bulgy ones first, as you suggest. I'm not really sure where to buy these things, as I have never tried anything like this before. I don't suppose you would know who might supply these in Ontario (Canada)? If not..... I'll hunt around.
Thanks again,
.... john
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Old 06-16-2011, 06:16 AM   #18
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Haven't a clue about shopping in Canada I'm afraid. look for shops that sell Electronic components .. In the USA it would be Radio Shack for example however I am not impressed with the equivalent stores of theirs in either the UK or Greece .. RS Components have an international reputation and there is always Digikey, both of whom I have dealt with for years.

better pay a little bit extra for quality than have to open and repair again in a few months time. And please remember that Electronic / Electrical Equipment are potentially lethal to anyone and everyone around .. not just the guy with his hands inside !!

Good Luck and I await to hear your news.
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Old 06-17-2011, 07:45 AM   #19
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Hi D_F,
I will get a back to you, but it may be some time before I do. Finding this stuff, and replacing them will take some time for me. I wish I had your expertise. It would probably be 'a piece of cake' for you. For me.... it's sortie into an unknown world.
Thanks again,
.... john
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Old 07-30-2011, 09:39 AM   #20
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Hi Done,
Well..... I finally have the capacitors.... a 1000uf and a 220uf. I forgot to mark which side was +ve and which was -ve on the board, but I think it's marked...... shaded side -ve/+ve side beige ... does this sound right to you? The capacitors themselves have a gray bar down the side, which is the short wire side. I'm guessing that this is the -ve side? The 1000uf says, "Chang -40-105°C1". The 220uf says, "KMC (M)105°C 2(2) 70" Are these OK?
Thanks,
.... john

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