Dell Monitor blinking LED

[Rtech]

Re: Dell Monitor blinking LED

The Bl_On Signal turns on Q757,which in turn turns on Q761,and that is the cct that supplies the voltage to the IC. I would suggest that you measure the DC Voltage on R754, before you press the on/off Button and see if it changes when you press the button. C764 I assume you have changed ??,so I would look closely at Q757,Q761, R752 and R754(both 10KΩ)

[retiredcaps]

Re: Dell Monitor blinking LED

I didn't get any DC Voltage on pin 9

If you don't have any voltage on pin 9, it could be one of two things:

1) IC is bad. With power off, see if VCC (pin 9) is shorted to GND (pin 8). Report your ohms reading.

2) The circuit path to pin 9 is bad. Take your multimeter and put it into continuity mode. Put one probe on pin 9 and the other probe on components that might have continuity to pin 9.

For example, pin 9 might have continuity to C764 and R787. You can either check those components to see if they are okay or check the DC voltage on them.

You know PF751 has 17V DC. You are just trying to find out why it doesn't reach pin 9. For example, an open resistor would stop 17V from getting to pin 9.

PS. Note to future readers, here is where picture orientation matters in post #1. The top power board is "right side up". The backside of the power board is "upside down". This forces regulars to download the picture, rotate it, etc (i.e. more work on our part).

[selldoor]

Re: Dell Monitor blinking LED

Perhaps it was for a different board/revision those colours are correct for
for that resistance 120ohms - you did have it lifted?

If you could post a clearer picture of the board so I can see the colours
a bit better I can do more looking tho it will be tomorrow now.

Maybe retiredcaps will come up with something later on regarding the results of the test you did for him.

[Pentium4]

Re: Dell Monitor blinking LED

10 ohms may be correct what are the band colours

Brown, Red, Black, Black, Brown

Unless I did it backwards

[selldoor]

Re: Dell Monitor blinking LED

So apparently R765 is a 120Ω resistor but it only measured out to 9.96Ω and testing the TL1451ACN, I didn't get any DC Voltage on pin 9

10 ohms may be correct what are the band colours

[Pentium4]

Re: Dell Monitor blinking LED

So apparently R765 is a 120Ω resistor but it only measured out to 9.96Ω and testing the TL1451ACN, I didn't get any DC Voltage on pin 9

[selldoor]

Re: Dell Monitor blinking LED

Okay I will do that just to be sure, black probe on pin 8 and red probe on pin 9? And just curious, why R765 specifically?

Yes, black probe on pin 8 and red probe on pin 9.

Apparently IC751 contains an oscillator circuit and frequency is controlled by C765 (470p 50v) and R765 - It is a 1% tolerance resistor and is critical for the circuit ( or I dont know - have just read it somewhere. )

[Pentium4]

Re: Dell Monitor blinking LED

Okay I will do that just to be sure, black probe on pin 8 and red probe on pin 9? And just curious, why R765 specifically?

[selldoor]

Re: Dell Monitor blinking LED

More things to check - with power off R765 (lift one leg) and , with power on check voltage across IC751 IF it is a (TL1451AC) then pin’s 8~ (ground) and 9~ (+15Vdc) there should be 15Vdc. Need to be careful pins are small and very close. Slip and its gone!!!.



EDIT Have you anything to check the ccfl bulbs on - so we know if they are going to work
eventually.

[Pentium4]

Re: Dell Monitor blinking LED

Let's get back to basics here.

1) Is the power LED on or off?

2) Is the power LED blinking or solid?

3) What is the DC voltage on U10 (logic board)? Report all 3 pins.

4) When you press the on/off button does BL_ON = pin 2 (connector) change from 0.0V to 3.0V DC? See

https://www.badcaps.net/forum/showpo...4&postcount=27

Remember that the main/logic board needs to signal BL_ON high in order for the backlights to come on.

In post 31, you only measured 5 out of the 10 pins. BTW, I prefer text based answers rather than paint. It helps with people searching in the future and makes it easier for us to read.

5) There are 4 blue tuning caps next to the ccfl connectors. I can see C736 and C756. With power off, measure the resistance across the legs of all 4 caps. They should all read open circuit on the higest resistance range.

1) On

2) Solid (And it will power off when I hit the power button)

3)
Pin 1 = 3.26V
Pin 2 = 0.00V
Pin 3 = 2.50V

4) Yes, it goes to 3.16V (Okay no more paint ) Do you want exact results on the other 5? I don't remember which is which but they either measured 3.3V or 5V

5) They all tested open

[retiredcaps]

Re: Dell Monitor blinking LED

Let's get back to basics here.

1) Is the power LED on or off?

2) Is the power LED blinking or solid?

3) What is the DC voltage on U10 (logic board)? Report all 3 pins.

4) When you press the on/off button does BL_ON = pin 2 (connector) change from 0.0V to 3.0V DC? See

https://www.badcaps.net/forum/showpo...4&postcount=27

Remember that the main/logic board needs to signal BL_ON high in order for the backlights to come on.

In post 31, you only measured 5 out of the 10 pins. BTW, I prefer text based answers rather than paint. It helps with people searching in the future and makes it easier for us to read.

5) There are 4 blue tuning caps next to the ccfl connectors. I can see C736 and C756. With power off, measure the resistance across the legs of all 4 caps. They should all read open circuit on the higest resistance range.

[Pentium4]

Re: Dell Monitor blinking LED

By the way, while checking this monitor, do you have the VGA cable connected to a running PC?

Yeah, and I can see the desktop with a flashlight

[budm]

Re: Dell Monitor blinking LED

By the way, while checking this monitor, do you have the VGA cable connected to a running PC?

[Pentium4]

Re: Dell Monitor blinking LED

They are probably ok then - I have been trying to find out what it should be 200 ohms seems low but they are all different.
In post 19 I mentioned resoldering the caps near the 5707s and you rplied that you had replaced all the caps. Those ones are not usually replaced so I am just checking that you have resoldered them C735 C755 C754 C734.

Think the primary one is okay too then? And alright I will resolder those caps. I meant I replaced all of the lytics

Sorry - but I have to ask - you are plugging the leads from the lamps into the board
when you are testing (I have known it heheh have even done it!!)

Haha, I understand. Yes I have been, double check every time

Edit: Resoldered, no luck yet Thanks for your continued help!

[selldoor]

Re: Dell Monitor blinking LED

Sorry - but I have to ask - you are plugging the leads from the lamps into the board
when you are testing (I have known it heheh have even done it!!)

[selldoor]

Re: Dell Monitor blinking LED

They are probably ok then - I have been trying to find out what it should be 200 ohms seems low but they are all different.
In post 19 I mentioned resoldering the caps near the 5707s and you rplied that you had replaced all the caps. Those ones are not usually replaced so I am just checking that you have resoldered them C735 C755 C754 C734.

[Pentium4]

Re: Dell Monitor blinking LED

POWER OFF
On the side with 3 pins first check on one transformer that the two pins close together are in fact joined - resistance 0.00 ohms. then check from either of those to the third pin. (meter on ohms 2000.) post results. Yes for all four transformers.
If they are ok we can go on to primaries.

All the adjacent pins tested good, and when checking to the 3rd pin they were all ~200Ω

[selldoor]

Re: Dell Monitor blinking LED

All 4 of them? What pins would I check?

POWER OFF
On the side with 3 pins first check on one transformer that the two pins close together are in fact joined - resistance 0.00 ohms. then check from either of those to the third pin. (meter on ohms 2000.) post results. Yes for all four transformers.
If they are ok we can go on to primaries.

[Pentium4]

Re: Dell Monitor blinking LED

I would check the secondary windings on the inverter transformers even tho
you dont see any flash. Perhaps also check the primaries but they rarely fail.

All 4 of them? What pins would I check?

[selldoor]

Re: Dell Monitor blinking LED

I would check the secondary windings on the inverter transformers even tho
you dont see any flash. Perhaps also check the primaries but they rarely fail.