Dell 3007WFP - 24V rail not working

[AmEv]

I've found out that the 24V rail isn't working on my brother's 3007. The panel itself works, and I get an image; the issue is that the backlight doesn't work.

Poking with a multimeter, I was able to confirm the other voltages were correct, but the 24V rail was outputting 0V, and it was neither a short nor a break.

I'm just not completely sure where to look next.

[budm]

Re: Dell 3007WFP - 24V rail not working

So for sure you do get the 18V, 12V, and the 5V?
You need to verify if you do have PS-ON, and if you do have boosted Voltage of around 380VDC between the two legs of the main filter cap or not.

[AmEv]

Re: Dell 3007WFP - 24V rail not working

I'm going to double-check, as it seemed the 24V rail was a constant source, due to backlight brightness being lost upon loss of AC, and the other rails going to the backlight being data rails (serial(?) brightness control and backlight on/off).


Will also get back to you on the other voltages.

Edit: 5V reading 5.3V.

Both STB rails reading 5.3V.

18V rail reading 18.5V.

Just to double-check, the main filter cap would be the huge one under the heat"bar", right? If so, either I'm not doing it right, or I'm getting no voltage across that cap.

[budm]

Re: Dell 3007WFP - 24V rail not working

Backlights ON/OF is just a stable state HIGH or LOW, usually >2VDC = Backlights ON, <1vdc = OFF.
The dimming control signal may be analog (0~5VDC, 5vdc = max lamps brightness) or may be PWM (10~90%) control signal.
PS-ON is also steady state control signal.
That power supply board has PFC Voltage booster circuit that is turned on when ps-on is present.

[AmEv]

Re: Dell 3007WFP - 24V rail not working

Speakers work, 12V rail is working properly.

I do remember voltage on the backlight on and backlight control rails; need to double-check those.

Also, which line is the "PSU On" lead? I've followed the traces for the backlight enable/adjust, but they lead straight to the inverter cable without break.

[budm]

Re: Dell 3007WFP - 24V rail not working

PS-ON is the command signal form main board to turn on the rest of the power supply, I.E. 24V.
Then you have BL-ON (Backlights ON) which also comes from the main board, this signal is delayed a little bit after the power supply is turned on and stabilized, this signal turn on the backlights circuits.
So you must have about 380VDC between the two legs of the main filter cap when PS-ON is present.
BLK EN (Backlights Enable) is the same as BL-ON.
BLK ADJ (Backlights level Adjust) is the same as Dimming control.

What DCV do you have on 'STBN24 12'N and 'STBN18V) when the monitor is OFF and when the power switch is activated.
We still need good clear straight shot pictures of the top and bottom side of the board so we trace out the circuit.

[budm]

Re: Dell 3007WFP - 24V rail not working

I went through my HD and found pictures and how I tested the board.
https://www.badcaps.net/forum/showth...d=1#post720156

LITEON PA-4151-1-LF

[AmEv]

Re: Dell 3007WFP - 24V rail not working

Here, let me get better lighting...

I'll get back to you with the voltages.

[AmEv]

Re: Dell 3007WFP - 24V rail not working

OK. The voltages for the "STBN" leads are 0V when the monitor is off, 5.3V when on.

I'm suspecting that those lines turn on the 18V and 12V lines when voltage is applied to them, and that the component(s) that turn on the 24V rail is out of commission.

[budm]

Re: Dell 3007WFP - 24V rail not working

https://www.badcaps.net/forum/attach...7&d=1485233865
Pin 9 is for 24V
Pin 12 is for 18V
So those two pins should be >2.5VDC when monitor is turned on.

https://www.badcaps.net/forum/showth...d=1#post720156

[Davi.p]

Re: Dell 3007WFP - 24V rail not working

There's any of the many images that explains how the 24v psu starts or work, i've marked with RED box the area that have to be photographed, and with YELLOW the area that i think it must be checked first, all components. Bye.

especially, 1 of the 2 optocouplers is made to transport to primary the enable signal, it must check around 5v on diode when monitor is on, on the primary (phototransistor) it must have 0v.