Dell 1905FP Powers on then black

[printone2]

This LCD will power on and the power button stays green as normal at all times when the the panel is turned on. When turned on the diagnostics screen displays for about 1.5 seconds then it goes dark. I have swapped a known good inverter in the panel and it performs the same way. I have not seen any caps that look abnormal on any of the boards. When I shine a light on the panel after it has gone dark, but is still powered up, but I do not see any image.

I have not been able to see if all of the lamps are coming on when the diagnostic display is working. I do not have an easy way to see the lamps turn on or swap them out. That is the direction I am headed next, but I am running out of ideas and would appreciate any help on other things to try. I do not have any other boards to swap with. The know good inverter I used just happened to be the same board as used in a good 1704FP.

Any help?
Thanks.

[Wrog]

Re: Dell 1905FP Powers on then black

Post pics of the top/bottom of both the power supply, inverter (if separate) and logic/main board (use "Manage Attachments" instead of linking inline, please). There is a treasure trove of information and test methods in this forum if you search for "two seconds to black".

[printone2]

Re: Dell 1905FP Powers on then black

Here are the pictures. I could not see an image once it went to black, even with a flashlight. The information that I find at about this LCD refer to the power and inverter as one board, but I believe that works, since a know good board gave the same performance. I have included several pictures of a board that is the width of the panel and therefore too long to get one good picture. Getting to the lamps looks intimidating. Thanks.

[retiredcaps]

Re: Dell 1905FP Powers on then black

Getting to the lamps looks intimidating.

If you have a spare working LCD, you can stretch the ccfl connector cable from the Dell to the spare and try and figure out which ccfl is actually bad.

[PlainBill]

Re: Dell 1905FP Powers on then black

Fairly easy test. Note the cable from the IPS (Inverter / Power Supply) to the logic card. The two wires closest to the middle of the board appear to be white and gray. Does the voltage on these two pins change when the CCFLs go off?

PlainBill

[printone2]

Re: Dell 1905FP Powers on then black

Plainbill, I am uploading a closeup of the back of the logic board showing the functions of the pins coming from the power supply. The middle pins appear to be be ground wires. Is the where you intended me to probe? My photography skills are weak, but here is how they schematic reads starting in the middle of the logic board and reading down towards the DVI port.

5v
5v
5v
GND
GND
GND
Audio DET
Audio EN
BKLT En
BKLT Adj

Does that make sense?

[printone2]

Re: Dell 1905FP Powers on then black

If you have a spare working LCD, you can stretch the ccfl connector cable from the Dell to the spare and try and figure out which ccfl is actually bad.

So I should just stretch my non-functioning panel's CCFL leads to a working CCFL tube already encased in a functioning panel? Does the CCFL tube need to also be a 19" tube or will a 17" tube in a 17" monitor also be sufficient?

I am guessing that each panel's leads control two tubes. If this is correct how do I decide which one is bad, or do I just order one and take a 50/50 chance that I am replacing the correct one? I could be wrong in my assumption that this monitor has 4 tubes, but that seems to be what my ready suggests.
Thanks.

[PlainBill]

Re: Dell 1905FP Powers on then black

Plainbill, I am uploading a closeup of the back of the logic board showing the functions of the pins coming from the power supply. The middle pins appear to be be ground wires. Is the where you intended me to probe? My photography skills are weak, but here is how they schematic reads starting in the middle of the logic board and reading down towards the DVI port.

5v
5v
5v
GND
GND
GND
Audio DET
Audio EN
BKLT En
BKLT Adj

Does that make sense?

Well, I wasn't real clear, was I? I was referring to the pins at the IPS, no biggie. The signal I am interested in is BKLT En. That should go high (> 3 Volts) to turn the backlights on. If it stays high when the backlights go off, the problem is either with the CCFLs or the IPS. Since you have tried a known good IPS, the conclusion would be the problem is the CCFLs or the wiring to them.

PlainBill

[retiredcaps]

Re: Dell 1905FP Powers on then black

So I should just stretch my non-functioning panel's CCFL leads to a working CCFL tube already encased in a functioning panel? Does the CCFL tube need to also be a 19" tube or will a 17" tube in a 17" monitor also be sufficient?

Yes, just stretch the wire to functional panel. Just make sure the 2 LCDs don't touch to prevent any potential shorts. I have done this before without any issues.

I am guessing that each panel's leads control two tubes. If this is correct how do I decide which one is bad, or do I just order one and take a 50/50 chance that I am replacing the correct one? I could be wrong in my assumption that this monitor has 4 tubes, but that seems to be what my ready suggests.

Try this, leave P102, 103, and 104 plugged into the Dell. Plug P101 into the functional LCD. Hookup a computer so you get a display to the Dell and watch for 2 seconds to black. If the Dell monitor stays on for more than 30 seconds, then the ccfl at P101 is bad or the wiring to the ccfl is bad.

If you get 2 seconds to black, leave P101, 103 and 104 plugged into the Dell. Plug P102 into the functional LCD.

Detailed instructions at (see section #5)

https://www.badcaps.net/forum/showthread.php?t=10419

Pay attention to the HIGH VOLTAGE and POWER OFF for 1 minute instructions.

[printone2]

Re: Dell 1905FP Powers on then black

Retiredcaps:
I started with your procedure and wired into the good panel. I only have four pairs of wires instead of eight, so I am guessing that means I only have 2 lamps.
I wired into the first sockets and I still go to black. I wired into the second pair and again the same results. From the way the panels are wired I am assuming that each lamp is powered independently of the other, so I thought that one of these tests would have lit a tube from the known good panel, but it did not. This points me to the conclusion that the lamps are not the problem. Is that right? One of my wiring setups is attached.
My guess is that polarity is not a problem. That the charge excites gas in the tube the same from either end. Is that correct because I have them next to each other so that the wires will reach. This makes them configured like in a head to head position and not head to toe, if that makes sense. They are from similar models, so the wires are going into the known good panel the opposite of what they normally would but still with the indicator dot showing consistently on the top of the male connector.
Thanks.

[alexanna]

Re: Dell 1905FP Powers on then black

Your monitors have four ccfls. 2 wires per connector=1 ccfl
The pictures indicate that you are using 2 ccfls from one monitor and 2 from another?
Hook all four ccfl connectors from the good monitor to the monitor that has the sec to black issue and
See if anything changes
Al.

[printone2]

Re: Dell 1905FP Powers on then black

Excellent idea. When I connect all leads to the good panel's tubes I do not get any video on either panel even with a flashlight. I do hear a noise for 1 to 2 seconds then it is still.

[alexanna]

Re: Dell 1905FP Powers on then black

You have a video source connected correct?
Can you describe the noise your hearing?
Al.

[printone2]

Re: Dell 1905FP Powers on then black

Is have the vga from my laptop's external video. The sound is similar to the servo motors spinning up for a CD ROM and then stopping, or like a play station that is having trouble detecting the type of disk in the drive. It starts up and spins a bit then goes silent.

Previously, I have just used the diagnostic screen from the lcd's ROM. My laptop is able to detect an external monitor attached and asks me what I want to display on it.

[alexanna]

Re: Dell 1905FP Powers on then black

Assuming you are serious and not pulling anyone's leg , about the noise.
I have absolutely no idea.
Al.

[printone2]

Re: Dell 1905FP Powers on then black

I am very serious. I have had panels make high pitched noises before, but this is like a mechanical noise that seems very out of place to me.

[retiredcaps]

Re: Dell 1905FP Powers on then black

.

[Rtech]

Re: Dell 1905FP Powers on then black

Plain Bill suggested you check the BKLT EN Voltage between the pin and any of the GND on the same plug..... and does it change etc ??we may be able to help more if you can give the resut of that test.

[printone2]

Re: Dell 1905FP Powers on then black

That voltage reads 3.25 when the panel is turned on and the backlights light up and then drops to zero in two seconds.

[printone2]

Re: Dell 1905FP Powers on then black

Under magnification that bklt en pin looks like a bad solder joint. I am not very good at soldering but the joint looks corroded and I can see what I would call copper traces in the board coming from that joint that are exposed. Possible has gotten hot. Could this just be a cold solder joint that is my problem?