PC Monitor Fail

[christos]

i got a monitor thats about 1 year..the problem happen 1 week ago and cant find what it is...the problem is that when i connect the monitor to the pc..it stays on for like 2-3 sec and goes black but i can see that the power led is still on..i found that if you decrease the brightless its stays on..i did that and for 1 hour it goes black again with 0 brighless..it was making a weird sound like sparks..any idea what that is?  they say that the capacitors are dead but i checked all of them and found that one 330nF cap was totaly dead..i changed it and still the same.. heres the foto http://postimg.org/image/ubf4eeigj/ this is the power supply for the monitor
can anyone help a bit?

 the vid

[mariush]

Power supply is probably fine.  Spark sounds would make me think one or several of the leads going to the fluorescent tubes is loose (unsoldered), making a poor contact.

That  capacitor circled in the picture is unlikely to be a real problem. You should check the ESR of the capacitors on the secondary side though, if you have a proper meter for it. Just because they look fine, they may still be somewhat bad.

[christos]

so a bad cap isnt alway inflatable?they may look like theyr ok but actually they isnt?i heard the noise at the 2 transformers that are the same...

[mariush]

Trying to explain as simple as possible...

There are usually 4 thin fluorescent tubes in the monitor, two at the top, two at the bottom.  These tubes work at around 700v but low current. Some monitors run the four lamps in parallel, others pair them, so you basically have two lamps in series and push close to 1500v through them to start them.

So the controllers basically work with two pairs of lamps and they have a sort of timeout period... they send power through the pair of lamps and they monitor to see if the lamps actually use current. If the current doesn't stabilize within a few seconds, the controller shuts down for safety reasons. If a wire at the end of one of those tubes is desoldered (and holding on just by the silicone jacket and sporadically making contact with the lamp metal pin at the end) the controller may detect there's no stable load on that pair of lamps and the controller will turn off after a few seconds.

Also, those tubes get weak as time goes by... but it usually takes years to become so bad as to cause problems. When a tube has too many hours, at the end of the tubes they usually become dark yellow or black and when they become this way, the current consumption of the tube increases. The controller detects this current increase and will also shut down, trying to protect those small transformers from overheating.

Now the controller needs stable voltage to power the inverter and the lamps... it gets this power from the secondary side of the power supply. If the esr of some capacitors there goes high, it's possible that when the controller pushes power through the inverter to the lamps then the bad capacitors may cause the voltage to go below a threshold and reset the controller or fool it into thinking the lamps are bad.

I would first check the end of the cfl lamps and make sure the wires are properly soldered - you have to be careful because it's hard to pull the silicon jackets from the end of the cfl tubes without breaking the wires and it's also somewhat difficult to put the panel back together.

[christos]

thx for the info..ill try to do that

[christos]

it realy was the light..i played  with the 4 cables and its working but i dont know if its going to do it again..can it be the 2 transformers or the cables?

[SeanB]

Cables most likely or the connections on the ends are broken loose from the wire inside or from the lamp pins.

[christos]

im not sure if its the cables but when i open the monitor and touch the cables its going off..maybe its the caps..but all are fine.the dont seem like they are dead

[mariush]

You're introducing some vibrations in the cable when you touch it. Most likely that's enough for the loose wire at the end of one of the lamps to break the connection and the inverter controller then turns off all four lamps for safety reasons.

Check the ends of the lamps first, before you make other assumptions.  Be careful and gentle and you'll be fine.

[SLJ]

While your in there replace all the caps or you will just be opening it up again soon.   If one went bad on it's own most likely all or most of them are crap.

[christos]

ill change all the caps and if its doing it again ill try the cables....its made in china bought in 2008 for like 80 euros..19" what do you recomend to do first? i went to a local elecronics store and the guy told me that the problem may be somewhere near the 2 transformer ..he recomend me to check the cables..he told me that the caps where fine..99% posibly that the caps are fine
thx for the help

[christos]

well it was the lamp..2 of 4 was burnd..and i cant find here in greece these lamps...New Monitor only:P   thx for the help..i didnt know that it may be the lamps..Learned something new..Thx again for the advice

[mariush]

You can order such lamps online, but they're not cheap if you include the shipping costs.

http://www.ccflwarehouse.com/ccfllamps.html
http://www.ccflwarehouse.com/cclawiwi.html

About $20 a tube, plus maybe 10-20$ for shipping to Greece. Sometimes it's cheaper to buy a faulty monitor from eBay of the same resolution and screen inches to extract the working ccfl lamps from it.

[christos]

i know that i can buy these tubes..but better to buy a new monitor to do my job..i ordered an LG LED for 100 euros+the cost to shipp it..if i bought lamap i would need 4 of them couz 2 of them was totaly broken and the other 2 was a bit black at the ends..at least i learned something new about monitors