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Viewsonic lcd screen

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limlik

New Member
So my LCD screens back light didn't come on one day. I just got around to taking it apart today. There are 3 possibly bad capacitors on it (Bulging tops on them one with a slight leak) so I will replace those. The main thing is that there are two chips on it I can't identify. There are 2 chips exactly the same, they are 8 pin chips with the this on it. P605 BZ6L1Y. The reason I ask about these is because around them the board looks slightly burned. I don't know if it was from these chips frying or if that is just how they were attached.


Sorry for cell phone quality.
 

sheldonstv

New Member
right what you need to do is replace those electrolytics with hi temp 105 degree types ,also make sure the voltage rating is the same or higher than what was fitted(if they are 10v rated fit 16-25v types)and the correct values capacitance wise are fitted ....the two ics may be ok altho 1 does look like its been running a bit hot make sure they are soldered in the board ok if you give me make and model i may have a manual
 

limlik

New Member
I just repaired another LCD the other day, dead capacitor on the Power supply. All chips are firmly soldered by the way. Will look for replacement capacitors tomorrow, should be easy. The screen model is VA1912wb.
 
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limlik

New Member
Also do you think the dead capacitors would be a possible reason for the backlight not to come on but the on led to come on?
 

Chippie

Member
Ok just got some capacitors so I will see what it does when I change them.
limlik,

Before you power it up, you should check around those two ics you highlighted earlier, just make sure there are no bad soldered joints around the pins..and anywhere else for that matter...especially where the pcb has got hot...heat will dry out a soldered joint!
 

limlik

New Member
The solders around the IC's look like they are in perfect condition I am glad to say, so after I do the solder I will plug it in.
 

XenonKilla

New Member
I just had this same issue with my Samsung Monitor in THIS THREAD Turned out the problem was two caps. Also if you look at the pics in my thread you will see that my power supply board has the exact same discoloration that yours does. I think it just has to do with the heat from the board. In any case my monitor did the same thing, I came home and hit the keyboard to turn my monitors on and only one of them came on. My power light would still blink and all that but no image would appear. Like I said turned out to be just two caps and now it's working like new again.
 

creakndale

New Member
Limlik,
Those two P605 chips each contain a P-Channel and an N-Channel Mosfet. They drive the primary windings of the inverter transformers which in turn drives the backlights. Those IC's do get warm so that discoloration is typical. IMO, manufacturers do not provide adequate heatsinking for those "drive" IC's. Eventually, one of the four Mosfets shorts out due to excessive heat causing a "shoot through" condition.

The Mosfets can be tested using a multimeter that has a diode test function.
MOSFET Testing using a Multimeter - ELEKTOR.com ? Platform for electronics and microcontrollers

Digikey has those IC's for 87 cents each:
Digi-Key - 785-1140-5-ND (Alpha & Omega Semiconductor Inc - AOP605)

creakndale
 

mneary

New Member
In addition to the MOSFETs running pretty warm, that type of PC board (often called "paper phenolic") turns brown at otherwise harmless temperatures.
 

REC

New Member
Sorry to bring to life an old thread. However, I am having a problem with my acer monitor. I have the board out and a few capacitors off. While looking on google to find out about the burn marks I came across this thread. I have the exact! same board along with the exact same burn marks/bad caps. I do not know if the person here has fixed their problem or not. If so, and he/she still reads this, what was wrong? If not, I just wanted to add that on my board the capacitor (up and to the left of the middle one you have circled in your picture) was also blown (CE102 on the board). I am going to buy a few tomorrow and solder them in. I will let you know if it works out!
 

REC

New Member
New capacitors in and everything works great! I replaced the two 1000/25v capacitors too along with the three you have circled (the one laying on it's side and the other I mentioned earlier). Hope that helps if you still have that monitor sitting around in a basement somewhere :p.
 

vedo35

Member
How old is your monitor? More than 5 years and u used long time every day or so?

Just my exprerience advice that i had same or almost same problems: " Monitor after open 3-4 seconds later going to standby . " probably reasons :
1- like your power supplay problems-bad caps ( you already changed ) if caps changed and still same and you are sure smps works perfect. Check the dead CCFL backlight florecents up and down ( one of them or both are dead) CCFL inverter controller ic controlls CCFL lamps. IF bad CCFL goes to sleep mode. On the photo 8 pin dil mosfets works driving the H.V transformers. So dont think immediate bad. Otherwise u woudnt see any screen for 3 seconds. Probably they are ok. Open gently lcd preotection aluminum covers and be very carefull when you take off them from acrylic reflector. Look to CCFL flamans if looks black than change the CCFL lamps.
 
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