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BenQ FP547 15" BLACK SCREEN
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tofutofu
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PostPosted: Sun Jan 22, 2012 12:16 am    Post subject: BenQ FP547 15" BLACK SCREEN Reply with quote

hello everyone.

trying to found the problem in the Q5x3 power board of my benq FP547 monitor.

the problem started with black screen every few minutes . but soon become black permanent.
conecting to power and a signal, giving a green light (recognize the signal).
i changed 2 puffed cap's. with no chang.

checking the voltage on bord:
the V-inverter is 13.3v (is that OK?). but no power is geting in to the 2 small transformers (cant see any Voltage after the fu9024n mosfet-[ Q751 and Q743 on the diagram]) .

I changed the 2 couple of transistors [Q759,Q760 & Q730,Q740 on diagram] (should be 2SC5706. but I got only the 2SC5707 that was available at store ) and replaced the 2 fu9024n mosfet. but no chang.

I'm working with the diagram, but don't have any clue what to do next.

any help or idea?

the diagram URL:
elektrotanya.com/benq_q5x3-304_power-bd_acer-547.pdf/download.html
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jts1957



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PostPosted: Sun Jan 22, 2012 1:24 am    Post subject: Reply with quote

Replace FP751 and resolder all terminals of T751 & T752.
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tofutofu
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PostPosted: Sun Jan 22, 2012 6:58 am    Post subject: need to וnderstend Reply with quote

jts1957 wrote:
Replace FP751 and resolder all terminals of T751 & T752.


thanks for your replay.
but the voltage after the fuse (pf571) is good (13.33v)...
should I replace it anyway?

does T751=Q751?

thanks
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tofutofu
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PostPosted: Sun Jan 22, 2012 7:33 am    Post subject: more data Reply with quote

the BLT_on voltage :

1)when starting, (no connection to vga source)- the green light is turning on for few seconds and the voltage is 3.3v as well (and then go to 0.0v)

2)when connection to vga source- the green light is turning on permanent- voltage is 0.0v

is that all-right?
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jts1957



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PostPosted: Sun Jan 22, 2012 8:36 am    Post subject: Reply with quote

Yes

T= Transformer
Q= Transistor
FP= Fuse
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tofutofu
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PostPosted: Sun Jan 22, 2012 10:54 am    Post subject: more data Reply with quote

tanks JTS1957, I will try that.


I just found out that when starting, (no connection to vga source)- the green light is turning on for few seconds and the voltage is 3.3v as well (and then go to 0.0v). then, the back-light is turning on for few seconds. with the message "NO SOURCE" on screen.



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tofutofu
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PostPosted: Mon Jan 23, 2012 2:24 pm    Post subject: Reply with quote

I i told before, I can see the back light turn on for few second
does that means the inverter is good?
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jts1957



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PostPosted: Mon Jan 23, 2012 3:47 pm    Post subject: Reply with quote

Try connecting one CCFL bulb at a time and see if each lights for a couple of seconds.
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tpfutpfu
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PostPosted: Tue Jan 24, 2012 12:39 am    Post subject: Reply with quote

jts1957 wrote:
Try connecting one CCFL bulb at a time and see if each lights for a couple of seconds.


tried that. both bulb are working separately for few seconds.


the BLT_ON voltage drop from 3.3v to 0.0v when the back light turned off (also when connected to VGA source)

I tried connecting 3.3v to the BLT_ON from other source. the back-light is turning on, then I can see the picture blinking on the screen every second (wile the back light is continually turned on).

anything to do from hear?
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jts1957



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PostPosted: Tue Jan 24, 2012 1:00 am    Post subject: Reply with quote

There should be FOUR bulbs - two top, two bottom. Since both bulbs on top (or bottom) share a holder, you must test them individually.


BLT_ON (backlights ON, active when LOW) - Backlights turn on for a couple of seconds ... what happens to the 3.3v/0volts?
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