Benq Fp71G / Q7T4 strange situation

[Davi.p]

It had the famous inverter problem, first i had changed only 2 of the 4 C5707 , the other 2 seemed not in short, 1 FU9024N and the .22 160v cap that was bulged if i remember, but i had taken the other from another FP71G+, it seemed ok with capacity but ESR i can't test, finally the picofuse.. the strange thing: i had tested it for approx 10 minutes as i always do for a first test before reassemble it, it goes well, another time, months after i retested it remounted, it appeared the logo for 1 second then black screen, i opened it and found (if i remember) the picofuse shorted, some c5707 shorted, i think 1.. i have removed the fu9024 , i don't remem. why, but found that it had a factory defect, it had a thin metallic piece between two legs, if i touched the center pin in a direction it makes contact, in the other no.. now i changed this , all 4 c5707 and the fuse and when i switch it on it starts with the logo but no all lamps on, then disappear logo and starts a white shadow from the upper right corner, it becomes bigger.. there is a video i made with cellular.. not so clear .. if vga is connected it appears the image for some seconds then if i remember disappears or become dark and also strange boxes and stripes can appears before, i can also feel a burnt smell, after i decide to switch off.. in the video i have pressed on/off at least 1/2 times to be able to show something... what situation it is? Is possible that firstly the fu9024 don't touches between legs and all was ok, then after with a flection of the case it is become shorted and the result is this?

The video: http://web.tiscali.it/bps_impianti/Benq-defect.avi

[EGuevarae]

Re: Benq Fp71G / Q7T4 strange situation

It had the famous inverter problem, first i had changed only 2 of the 4 C5707 , the other 2 seemed not in short, 1 FU9024N and the .22 160v cap that was bulged if i remember, but i had taken the other from another FP71G+, it seemed ok with capacity but ESR i can't test, finally the picofuse.. the strange thing: i had tested it for approx 10 minutes as i always do for a first test before reassemble it, it goes well, another time, months after i retested it remounted, it appeared the logo for 1 second then black screen, i opened it and found (if i remember) the picofuse shorted, some c5707 shorted, i think 1.. i have removed the fu9024 , i don't remem. why, but found that it had a factory defect, it had a thin metallic piece between two legs, if i touched the center pin in a direction it makes contact, in the other no.. now i changed this , all 4 c5707 and the fuse and when i switch it on it starts with the logo but no all lamps on, then disappear logo and starts a white shadow from the upper right corner, it becomes bigger.. there is a video i made with cellular.. not so clear .. if vga is connected it appears the image for some seconds then if i remember disappears or become dark and also strange boxes and stripes can appears before, i can also feel a burnt smell, after i decide to switch off.. in the video i have pressed on/off at least 1/2 times to be able to show something... what situation it is? Is possible that firstly the fu9024 don't touches between legs and all was ok, then after with a flection of the case it is become shorted and the result is this?

The video: http://web.tiscali.it/bps_impianti/Benq-defect.avi

Cold solder points.

[Bobdee]

Re: Benq Fp71G / Q7T4 strange situation

It had the famous inverter problem, first i had changed only 2 of the 4 C5707 , the other 2 seemed not in short, 1 FU9024N and the .22 160v cap that was bulged if i remember, but i had taken the other from another FP71G+, it seemed ok with capacity but ESR i can't test, finally the picofuse.. the strange thing: i had tested it for approx 10 minutes as i always do for a first test before reassemble it, it goes well, another time, months after i retested it remounted, it appeared the logo for 1 second then black screen, i opened it and found (if i remember) the picofuse shorted, some c5707 shorted, i think 1.. i have removed the fu9024 , i don't remem. why, but found that it had a factory defect, it had a thin metallic piece between two legs, if i touched the center pin in a direction it makes contact, in the other no.. now i changed this , all 4 c5707 and the fuse and when i switch it on it starts with the logo but no all lamps on, then disappear logo and starts a white shadow from the upper right corner, it becomes bigger.. there is a video i made with cellular.. not so clear .. if vga is connected it appears the image for some seconds then if i remember disappears or become dark and also strange boxes and stripes can appears before, i can also feel a burnt smell, after i decide to switch off.. in the video i have pressed on/off at least 1/2 times to be able to show something... what situation it is? Is possible that firstly the fu9024 don't touches between legs and all was ok, then after with a flection of the case it is become shorted and the result is this?

The video: http://web.tiscali.it/bps_impianti/Benq-defect.avi

Hello
Have you by any chance replaced a component in back to front (thinking maybe a FU9024N) it has been done by a few of us
...
There are another 4 threads on this Forum with your model Q7T4 worth a read, they may help

[Davi.p]

Re: Benq Fp71G / Q7T4 strange situation

To Eguevarae, i have forgotten, i had also resoldered from the first time most of the solder joints in little transformers (4) watching them thrugh a magnifing glass..
To Bobdee, i was following a thread on the Q7T3, very similar, but it never ends, is difficult to read for me because of the language... "Have you replaced a component in back to front (thinking maybe a FU9024N).." what do you mean? If i have put one of them in the wrong way? I made much attention, it's not possible.. thanks anyway.
...
I take this opportunity to say to all members to not come in discussion and say:
"i have the same problem... please help me.." or other unuseful entries because some
thread are too long to read.. and .. reduce the massages to the essential and *possibly*, for us not english practice, not use too many coloured words and slang that makes mistake to us, apart this very appreciated forum, thankyou.

[Davi.p]

Re: Benq Fp71G / Q7T4 strange situation

I have done a brief check and found that one of the lamp connectors was not rightly insterted, but by another test the sympthoms are near the same, i plug the power cord in and i already see a white shadow in the upper corner, if i switch on i see the logo, but not all lamps on, this time no burnt smell, when it was cold after benq logo it showed the pc image for few seconds then the brightness decreased instantly to quite dark then gradually darker, i switched on/off and newly the logo but after some try the pc image stays on, it stays full bright for a second then decreases instantly to enough brightness to see well but not full, maybe one lamp not at full bright or not on at all, always if i switch off or between the logo and pc image or when pc changes resolution so no video output, screen shows a white spot in the corner that increases the more rapidly the more warm is the monitor, in the background i see also the pc image with some bars and boxes in the middle, i've saw a maybe a similar issue with a 15" lcd monitor that i bought without ext. power supply , it had a wrong connector scheme drawn on the case and i have put one with inverted polarity, now works, but if no pc image is coming in it shows monitor warn with a strange colors background.
In the end i suspect a damage to the panel by inverted polarity or something similar.
thank for attention.

[Bobdee]

Re: Benq Fp71G / Q7T4 strange situation

Hello again
Have you tried unpluging the connector to the video board that goes to the panel, then power on, if its is the panel then you should be showing a bright white screen that does not turn off untill you turn monitor off.
...
Can you post some picture of top and bottom of PSU/Inverter board, this will help member to help you, they may see something that you may have missed

[Davi.p]

Re: Benq Fp71G / Q7T4 strange situation

It's a strange sub-type , it has has a video board that is included with the panel,
so i will try to get inside of it, apart this, when monitor is warm enough (after 2-3 minutes) when there's no pc input, screen stays near all white, this sounds like when the monitor is on and vga picture is present the panel is fully on and shows a good image, apart the reduced backlight, when he goes off he shows 1 instant a black screen but after he doesn't remain off but try to 'off' but goes off slowly with the picture's buffer memory fades slowly to all pixels 0 (or 1) = white , seen panels are 'normally white', or what is i don't know..

[Davi.p]

Re: Benq Fp71G / Q7T4 strange situation

I have solved the problem , it was a bad soldering job, i don't know how it happened but there was a broken pad on the fu9024 that i have changed that i don't have connected i dunno why to the circuit, so it went ultra hot when put the ac in, now it works, tested for some seconds, i hope it lasts. But now i have another problem, there was two little scratches on screen that doesnt made much visual problems when running, tend to black only, to mask them for cosmetical purp. i have put a little bit of
spray transp. paint applied with a tip, now when i put it on the back light pass through! (( It seems a problem with the polarizing film, like the paint don't leave to
polarize or it had changed chimically the polarizer, how can i fix it? Thanks.

[Davi.p]

Re: Benq Fp71G / Q7T4 strange situation

No, nothing, i leave it as is..