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BenQ FP547 15" BLACK SCREEN
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tofutofu
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PostPosted: Tue Jan 24, 2012 8:19 am    Post subject: Reply with quote

jts1957 wrote:
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?


1) I checked the bulbs separately (2 each time as they'r connected pair's )- and both working .

2) what do you mean by "backlights ON, active when LOW" ? should the backlight tern on when BLT_on is 0.0v?

when I'm checking BLT_ON on starting :
a) bulb's turn on for few seconds, then BLT_ON is 3.3v
b) bulb's turn off, then the BLT_ON is 0.0v
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tofutofu
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PostPosted: Tue Jan 24, 2012 8:29 am    Post subject: Reply with quote

how can I check each bulb separately?
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jts1957



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PostPosted: Tue Jan 24, 2012 10:20 am    Post subject: Reply with quote

BLT = backlight
_ = active ("On") when signal is "low"

If you don't check bulbs separately, how do you know if BOTH are lighting?

Bulb wires should be either two pinks with one white (or black) return OR one pink & one blue with one white (&/or black) returns.

Disconnect a wire by carefully removing from connector. Either a plastic or metal clip holds in place.
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tofutofu



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PostPosted: Tue Jan 24, 2012 5:05 pm    Post subject: Reply with quote

I'm almost sure that I have only 2 bulbs: one up and one down. from each connector I can see only 2 wires: one red and one white. (maybe I'm wrong)

so, I disconnected each one at a time and could see the backlight turn on for few second looking if the light is at the same strength.
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jts1957



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PostPosted: Wed Jan 25, 2012 1:39 am    Post subject: Reply with quote

My bad. Downloaded service lit. from ET, and sure enough ... only two sockets / bulbs.

Have you resoldered ALL transformer joints mentioned earlier?
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tofutofu



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PostPosted: Wed Jan 25, 2012 7:57 am    Post subject: bad trnsfotmer? Reply with quote

I will do the resolder as soon as possible . but I checked the output voltage of it, also compering to BLT_ON voltage :

checking the transform T601 onboard (not connecting to power), I could see that terminal 1,2,3,4,5 are all shortcut between each other. (making "beep" on the multimeter).
(is that normal or mean the transform is bad?)


checking T601 output voltage and "playing" the start button, I could see changes when green light off/on (not connected to VGA source):

terminal1=0.2 /0.7
terminal 2=0 /0
terminal 3=0 /0
terminal 4=3.0 /6.7
terminal 5=2.5 /5.6

(*I'm not sure if the unit are volts... as the multimeter is set on " ACV , 200")


checking the Transform Output (TO)(assuming it's AC) related to BLT_ON voltage (DC) wile connecting/disconnecting VGA source:
* checked the TO on the D702 terminal

1) NOT connected :TO=0.2 ,BLT_ON=0.0V

2) connected: TO=0.4. BLT_ON=0.0v

3) disconnecting:
TO: first no change (0.4) then raise to 0.8 and go down to 0.2 (when the green light shut down)
BLT_ON: first no change (0.0v) then raise to 3.3v and finely drop back to )0.0v (wile the green light shut down)

( in last case, when the BLT_ON raise to 3.3v' the backlight turn on shortly )
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jts1957



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PostPosted: Wed Jan 25, 2012 5:32 pm    Post subject: Reply with quote

Let's try for the "DC" voltage readings on the power supply diode cathodes.

D701 (pin 2) ground to C703/C704 "negative" terminal (approximately {~}13VDC);
D702 cathode ground to C703/C704 "negative" terminal (~3.3VDC);
D703 cathode ground to C703/C704 "negative" terminal (~less than 25VDC)
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tofutofu



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PostPosted: Wed Jan 25, 2012 6:57 pm    Post subject: Reply with quote

D701 (pin 2) ground to C703/C704 "negative" terminal:
1) 12.67VDC at starting -(BLT_ON 13.4v & backlight turn on) ,
2) 13.72 when connected to VGA source,
3) 14.45VDC "normaly"

D702 cathode ground to C703/C704 "negative" terminal (3.54VDC);

about D703 - I don't have it on my board- as my LCD have no speakers.
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jts1957



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PostPosted: Wed Jan 25, 2012 7:40 pm    Post subject: Reply with quote

Let's try that again.

Red DVM lead (DVM set to DCV) connected to D701 (pin #2), Black DVM lead connected to ground at C703/C704 "negative" terminal (you should get approximately {~}13VDC ALL Time - whether the set is only plugged in, irregardless whether the power button has been pressed or not);
Red DVM lead connected to D702 cathode, Black DVM lead connected to ground at C703/C704 "negative" terminal (you should get ~3.3VDC ALL Time - whether the set is only plugged in, irregardless whether the power button has been pressed or not).
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tofutofu



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PostPosted: Wed Jan 25, 2012 9:26 pm    Post subject: Reply with quote

jts1957 wrote:
Let's try that again.

Red DVM lead (DVM set to DCV) connected to D701 (pin #2), Black DVM lead connected to ground at C703/C704 "negative" terminal (you should get approximately {~}13VDC ALL Time - whether the set is only plugged in, irregardless whether the power button has been pressed or not);
Red DVM lead connected to D702 cathode, Black DVM lead connected to ground at C703/C704 "negative" terminal (you should get ~3.3VDC ALL Time - whether the set is only plugged in, irregardless whether the power button has been pressed or not).


OK, the voltage is changing between D701 (pin #2) TO C703 "negative" and going "crazy" when connecting/starting/normal..

(by the way, isn't it the same as the voltage between C703 positive & negative?)

the voltage between D702 cathode to C703 "negative" is steady 4.54v all Time.

thanks..[/b]
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