Dell Monitor blinking LED

[retiredcaps]

Re: Dell Monitor blinking LED

See if picofuse PF751 (right above the big filter cap) is blown after you replaced the c5707s.

See if Q743 and Q751 are shorted. These may the FU9024s I refered to as per post #18 and post #2 by UniT3d.

If the above are all good, then you will have to check the main board and make sure that BL_ON is > 3.0V DC.

[Lumberjack777]

Re: Dell Monitor blinking LED

See if picofuse PF751 (right above the big filter cap) is blown after you replaced the c5707s.

See if Q743 and Q751 are shorted. These may the FU9024s I refered to as per post #18 and post #2 by UniT3d.

If the above are all good, then you will have to check the main board and make sure that BL_ON is > 3.0V DC.

Yes. I have fixed about 7 of these: and in most cases it was the c5707's. But, in one instance it was the FU9024. And once it also had a blown picofuse. I'm betting its one of those FU9024's you mentioned.

[selldoor]

Re: Dell Monitor blinking LED

I replaced those transistors, replaced all the caps, and re-soldered all the joints of the 4 inverter transformers. Now it will turn on but I have to use a flashlight to see a picture. Could one of the inverters be bad?

Does the screen flash at all when you switch on?

If it does then it could be one of the transformers though they dont often fail on this
board - meter on 2000ohms check the secondary windings ( Think it is the two pins on one end there are 3 but 2 are conneted)

[Rtech]

Re: Dell Monitor blinking LED

On many occasions,when one of the Fu9024s go short,you get a situation where the screen is totally white when you apply Power WITHOUT the On button being pressed, and then it works normally when the On button is pressed.If they test good I suspect one of the CCFLs has failed.

[Pentium4]

Re: Dell Monitor blinking LED

Thank you very much for the replies PF751 is good

Testing between pins C and E on Q743 and Q751, they are both shorted

When it first turns on I don't get a flash at all

[retiredcaps]

Re: Dell Monitor blinking LED

Testing between pins C and E on Q743 and Q751, they are both shorted

Capking sells the fu9024 (post #18). I would get a few for future Benq boards.

[budm]

Re: Dell Monitor blinking LED

That fu9024 is driven by the PWM IC, the output is Variable DC depends on the pulse width of the drive signal from the PWM IC, the wider the width the more DC feeding the Royer Oscillator, the brighter the lamps get, if the fu9024 has shorted Source to Drain, the Oscillator will run at full power (max DC feeding the oscillator, max LAMP brightness) as explained by RTECH.

[Pentium4]

Re: Dell Monitor blinking LED

Interesting I ordered 10 of those FU9024N's, hopefully it will fix the issue!

[Pentium4]

Re: Dell Monitor blinking LED

Okay so I replaced both of those FU9024N's and it's still having the same issue. Not even a brief flash when it powers up

[retiredcaps]

Re: Dell Monitor blinking LED

What are the DC voltages on the connector between the power and main board?

[Pentium4]

Re: Dell Monitor blinking LED

What are the DC voltages on the connector between the power and main board?

I know, I suck with paint

[retiredcaps]

Re: Dell Monitor blinking LED

Verify that you have DC voltage on pf751 (both sides) wrt to cold ground. What is reading for both?

[Pentium4]

Re: Dell Monitor blinking LED

I'm only getting 0.0125V on both sides of PF751

[Pentium4]

Re: Dell Monitor blinking LED

I'm not sure if it means anything but R615 reads 0.4Ω both ways and all the other resistors around it get an actual reading (Around 70-100Ω)

[selldoor]

Re: Dell Monitor blinking LED

I'm not sure if it means anything but R615 reads 0.4Ω both ways and all the other resistors around it get an actual reading (Around 70-100Ω)

You usually have to lift one leg of a resistor to check it properly.
The measured resistance should equate to the the colour bands.

http://www.hobby-hour.com/electronic...calculator.php

[Pentium4]

Re: Dell Monitor blinking LED

You usually have to lift one leg of a resistor to check it properly.
The measured resistance should equate to the the colour bands.

http://www.hobby-hour.com/electronic...calculator.php

Ohhh okay thank you. It's a 0.22Ω resistor

[retiredcaps]

Re: Dell Monitor blinking LED

What is the DC voltage for each of the three ICs mounted on the heatsinks in the upper right hand corner?

Report each pin (BCE) with respect to ground.

[Rtech]

Re: Dell Monitor blinking LED

You show you are getting 3v and 5v,so the only thing missing is the 12v,which feeds the Inverter via the PF751.This is rectified by D701,which is a Schottky,and you should be able to measure it across C703,C704 and C712.

[Pentium4]

Re: Dell Monitor blinking LED

What is the DC voltage for each of the three ICs mounted on the heatsinks in the upper right hand corner?

Report each pin (BCE) with respect to ground.

Thanks for the persistent replies! Here are the readings
#1
E = 0.00V
C = 17.26V
B = 0.00V

#2
B = 0.00V
C = 5.00V
E = 0.00V

#3
1 = 2.12V
2 = 0.00V
3 = 3.30V
4 = 5.00V

You show you are getting 3v and 5v,so the only thing missing is the 12v,which feeds the Inverter via the PF751.This is rectified by D701,which is a Schottky,and you should be able to measure it across C703,C704 and C712.

I will check those other pins too and see what I get!

[retiredcaps]

Re: Dell Monitor blinking LED

#1
E = 0.00V
C = 17.26V
B = 0.00V

So the 12V is there. That 17.26V is unregulated and should drop down once the backlights are on.

Let's confirm you are measuring the DC voltage on the picofuse correctly.

1) Put your black probe on a ground screwn.

2) Put your red probe on one side of the picofuse? What is this reading?

3) Put your red probe on the other side of the picofuse? What is this reading?