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Problem I found the problem with my monitor it was the fuse so i replaced the fuse it came on and flashed then went off again so i checked the fuse and it was blown could this be a high voltage problem or something else

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  • Annette May 31, 2008

    I have checked all the 4 transistors the ones that are mounted on the heat sinks could not find a short on them there is one that has 4 legs not sure if im checking it right

  • Annette Jun 02, 2008

    The monitor is a Benq 17" model No. Q7T3 the markings on the transistors that are mounted to the heat sink are No 1 has four legs to it PO3RD23, No 2. YG902C2, No 3 is the same number as 2, No. 4 K9264 i will give you some more specifics on the problem was not working so i pulled the monitor apart and the backlights were not working checked all the transistors then one i just described thye came up with no shorts at all that I could find was the PF751 which i beleive is a 3 amp pico fuse MS 3A which was its markings found to be blown i put a replacement fuse in thinking that it may only be a fuse as i had checked most of the other components could not find anything with a short so plug the board back in hoping for the best what i got was the monitor come on for a split second showed the logo and then went off i went back and checked the fuse and it was blown check and replaced most of the caps hoping there was a faulty cap and i was still unable to locate any defent fault i decided to take a chance since i did not have much to lose and put a higher value fuse in place of the one that blew but this time fuse did not blow the backlinght and screen came back on for appros 2 - 3 seconds then shut down which i believe it has a safty shut down u can switch it on and it will do the same thing time and time again only for having the higher ampage fuse in it i believe it would be blowing the fuse maybe im having a punt here where it leads me to think there is a resistor gone high and allowing to much current in that part of the circuit thats a stab in the dark on my thoughts would be much appreciated if u can lead me in the direction that would solve the problem thanks Annette

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There is no "Flyback transformer" in the LCD monitor "Benq 17" model No. Q7T3". Such a component, a "Flyback transformer" is found in televisions and in Picture Tube type monitors. The red wire of a "Flyback transformer" is where 27,000 VOLTS comes out of to connect to the picture and such a voltage IS DEADLY so never enter a TV or computer monitor unless you know exactly what you're doing. To bring your hand too close to the "Flyback transformer" is to GET ZAPPED, you don't even have to TOUCH that transformer or the Red Wire that comes out of it!!!!

As far as a fuse blowing, NEVER PUT IN A FUSE WITH A HIGHER AMPERAGE RATING: it's there to protect certain components from being permanently damaged. If the fuse is blowing you must find out "why". There's got to be a short circuit in one or more components. Transistors, Diodes and Capacitors are easy to check for shorts. Transistors, Diodes are usually what short out. There's not much more I can say here.

A schematic diagram that shows the voltage on the many components of a running LCD circuit is what you need to find out where volatges should be. If a voltage is missing you must find out where the problem stems from. There are other ways to test circuitry, with an oscillascope and a schematic diagram that shows test points and the wave pattern that's suppose to be present.

Posted on Dec 03, 2008

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Most likely the horizontal output transistor that has shorted. This will be a large transistor attached to a heat sink close to the flyback transformer (part with large red wire coming out the top). Post hte marking here and I'll give you the full part number.
Dan

Posted on May 31, 2008

  • ABRsvcs Jun 02, 2008

    List the markings on the four transistors here as well as the make and model of the monitor and I'll try to post specifics.

    Dan

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My first advice is to ensure that your AC source(outlet) is live. Try to plug it in to a known working outlet to confirm that the power source is not the issue. If you are using a surge protector/AVR, try to directly plug the monitor's plug to the outlet.


If you confirmed that the AC source is not the problem, then this is an indication that the fault is inside the unit. You have to check first the power supply board's fuse. Check its continuity, if it has a continuity, then the fault is on the voltage regulator circuitry and/or other circuitry on this board, I would advice you to replaced the entire power supply board. Click it here for the replacement.


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