Top Half of Dell E151FPb Darker

[11flint]

Hello to all This is my first time posting.

I recieved a Dell E151FPb that the owner didn't want anymore due to "white screen" issue after the monitor would warm up a bit.

edit note* I forgot to mention that the original "white screen" issue the previous owner had was likely due to a desoldered joint on coil whose number I can't recall. There was talk of this issue in another forum, and indeed this same coil had the similar symptom on my power board.

I hastily opened the casing to see what could be at fault, and noticed the monitor used the "usual suspect" C5706/C5707 transistors, and two IRFU024N hexfets. Being naturally inclined towards laziness, I decided to do absolutely zero troubleshooting, and just change the above, along with a few filter capacitors.

I did not have IRFU024N hexfets, so I used two IRLZ34's, which have similar specs. In any event, the monitor turns on, but there are three new symptoms:

1) Top half (more like top 35%) of screen darker. (dying lamp?)

2) Monitor does not go to sleep (green led does not go amber when computer powered off)

3) Monitor does not power-off. When attempting to do so, LED shuts off, but you are left with "white screen", so I'm guessing the lamps are still drawing juice from discharge?

I have no idea what's wrong :\

Many thanks for your time and patience.

[alexanna]

Re: Top Half of Dell E151FPb Darker

Did you bridge a solder pad on one of the FETs?
Pictures would really be helpful, Please use managed attachments

[11flint]

Re: Top Half of Dell E151FPb Darker

Please excuse my ignorance, but what is a solder pad? Will post picks soon.

[alexanna]

Re: Top Half of Dell E151FPb Darker

pictures would be good
please both front and back of the board

[11flint]

Re: Top Half of Dell E151FPb Darker

Simply plugged in:



On, no input:



On, with input. Simple orange jpg fullscreen to hopefully highlight illumination problem:



Board pics coming up.

[smason]

Re: Top Half of Dell E151FPb Darker

Some questions:
Is the brigter area too bright or the dimmer area too dim?
Are both areas affected by the brightness/contrast control?

Just looked at the pics again.

In the middle pic, is the box displayed really that over-bright, or is the photo over-exposed?
In the last photo, you say that's an orange jpg? I'd say the bottom lamps are over driven.

If you hadn't done any other work on the montitor, I'd suspect dying lamp on the dim side, but it could just as easily be a transistor problem driving the lamps too bright.

[11flint]

Re: Top Half of Dell E151FPb Darker

The middle picture is overexposed. The box is not that bright.

Before I changed the hexfets, illumination was even (I think :|), that is before the screen would "white-out". The IRLZ34's I substituted with have a much higher Id rating then the original mos's.

Could it be maybe one of the transformers have lower resistance then the other, drawing more current?

[11flint]

Re: Top Half of Dell E151FPb Darker

IRLZ34 in red circle. Original suspect coil in yellow:



under:



Sorry, photography is not my strongpoint.

[11flint]

Re: Top Half of Dell E151FPb Darker

Is something maybe touching chassis ground that shouldn't be?

[smason]

Re: Top Half of Dell E151FPb Darker

In that case I'd suspect the FETs or the soldering of the FETs/5707s.
In my experience transformer problems (shorted windings) usually cause the inverter to shut down after a few seconds.You didn't answer whether the brightness/contrast controls affect both areas. That might give a clue as well.

[11flint]

Re: Top Half of Dell E151FPb Darker

Thanks for that smason. I'll try the controls in a moment.

[smason]

Re: Top Half of Dell E151FPb Darker

Not to be picky but, the photo of the top is adequate, the bottom one could stand to be sharper.

[11flint]

Re: Top Half of Dell E151FPb Darker

Brightness control doesn't have any effect at all, in other words, nothing gets brighter or dimmer.

Contrast goes up and down evenly.

[Wizard]

Re: Top Half of Dell E151FPb Darker

Sounds like one CCFL is dying at top. Replace the CCFL.

Cheers, Wizard

[11flint]

Re: Top Half of Dell E151FPb Darker

Me thinks you're right sir.

[PlainBill]

Re: Top Half of Dell E151FPb Darker

Sorry, but I must disagree. The important point is the backlight never turns off. You have either shorted out (or reversed) one of the FETs, or the control signal to the FET. Normally the inverter controller will modulate on time for the Royer oscillators, turning them off completely when the backlights are to be turned off. With one side blocked full on, it reduces the drive signal to the other oscillator, thus the brightness pattern.

PlainBill

[11flint]

Re: Top Half of Dell E151FPb Darker

I think I need to retract my previous agreement and resubmit it to you plainbill! Changed the ccfl, and no change To be honest, I have a feeling I placed one of the fets in backwards, but the schematic has both both FET gates placed on resistor junctions, so I followed the schematic instead of the printed GDS on the board, but something didn't seem right.

At the end of the day, it is ending up to be too much work, for a monitor I can sell for only 30$ at best

[PlainBill]

Re: Top Half of Dell E151FPb Darker

I think I need to retract my previous agreement and resubmit it to you plainbill! Changed the ccfl, and no change To be honest, I have a feeling I placed one of the fets in backwards, but the schematic has both both FET gates placed on resistor junctions, so I followed the schematic instead of the printed GDS on the board, but something didn't seem right.

At the end of the day, it is ending up to be too much work, for a monitor I can sell for only 30$ at best

You've already put in what - $5 in parts and a couple of hours? If you quit now you have wasted the time and money, and every time you walk by the monitor you will hear it snickering - "Ha, ha, couldn't fix me!!!". Fix it by replacing the backward FET and you can recover the money, get at least some compensation for your time (the balance of the time can be written off as 'training'), AND get the monitor out of your shop.

PlainBill

[11flint]

Re: Top Half of Dell E151FPb Darker

Thanks PB I'm already in the process of reversing the damage Yes, the monitor did cost 5$ (and then 6$ for the fets! lol!)

[jetadm123]

Re: Top Half of Dell E151FPb Darker

Since you didn't check the original IRFU024N's, maybe they're still good and you can reuse them.