Dell 1905FP Powers on then black

[alexanna]

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?

Try re soldering it.


There is a possibility that the resolution setting is wrong, on the laptop you are using
Can you get a hold of a desktop computer and recheck the B.L. on siginal.
To rule out all possibilities use a vga siginal and do not rely on the LCD rom as a siginal.
Al.

[printone2]

Re: Dell 1905FP Powers on then black

Okay. I am resoldering and will move to a desktop.

[printone2]

Re: Dell 1905FP Powers on then black

Same result on a desktop. I get 3.25+ and then it goes to zero. My solder job is not too pretty, but it is what it is.

[printone2]

Re: Dell 1905FP Powers on then black

The logic board has 10 caps on it. They all look normal, but I guess that does not say much.

[alexanna]

Re: Dell 1905FP Powers on then black

with the LCD hooked up to the desktop,re check for a immage with a flashlight.
Al.

[printone2]

Re: Dell 1905FP Powers on then black

No the image is not there with a flashlight either.
Thanks.

[alexanna]

Re: Dell 1905FP Powers on then black

No the image is not there with a flashlight either.
Thanks.

To me it's sounding like a logic card problem, Can you verify 5v is coming into and staying there on the three pins of the logic card, It might also be best to use the ground pins on the logic card for your DMM ground.
Al.

[printone2]

Re: Dell 1905FP Powers on then black

Yes, the three pins on the logic card are showing 5.25v on each of the three pins using the related grounding pins on the logic card. I too believe it all points to the logic card.

[alexanna]

Re: Dell 1905FP Powers on then black

Can you check the voltage regulators on the logic card?
Al.

[Rtech]

Re: Dell 1905FP Powers on then black

With the Power Supply/Inverter ONLY,ie NO Logic Card.Plug in all lamps,put approx 3volts from an external battery,between the BKLT ENable pin and the GND Pin on the Board,and then switch the Mains on...Does the Lamps light for a lot longer then when everything is normal ??????/

[printone2]

Re: Dell 1905FP Powers on then black

I do not know what a voltage regulator looks like, or how to test it.

I also do not know how to bypass the logic card and supply 3volts to backlight enable.

I have reached the limits of my abilities. I am going to close this panel up and consider this one finished. I have learned much, and do appreciate all the help and support each of you have provided. Thanks again.

[geep6]

Re: Dell 1905FP Powers on then black

i have this same monitor found it in dumpster when i hook it up to my desktop and power it on the lamps in it light up and the power stays on green light does not go off it does not show anything on the screen no self diagnostic nothing unhooked from the pc same thing nothing on screen does not show no signal message like most of them i opened it up all the caps in it look ok the caps are capxon 470uf 35v kf c440 don't know if these are known to be junk or not i don't think its the power supply how do you test the voltage regulators on the logic card do you just take them out of circuit and see if they are bridged

[retiredcaps]

Re: Dell 1905FP Powers on then black

i have this same monitor found it in dumpster when i hook it up to my desktop and power it on the lamps in it light up and the power stays on green light does not go off it does not show anything on the screen no self diagnostic nothing unhooked from the pc same thing nothing on screen does not show no signal message like most of them i opened it up all the caps in it look ok the caps are capxon 470uf 35v kf c440 don't know if these are known to be junk or not i don't think its the power supply how do you test the voltage regulators on the logic card do you just take them out of circuit and see if they are bridged

After the second line, I gave up reading. I can't understand where one thought begins and ends.

Please try to use some proper punctuation.

[jetadm123]

Re: Dell 1905FP Powers on then black

i have this same monitor found it in dumpster when i hook it up to my desktop and power it on the lamps in it light up and the power stays on green light does not go off it does not show anything on the screen no self diagnostic nothing unhooked from the pc same thing nothing on screen does not show no signal message like most of them i opened it up all the caps in it look ok the caps are capxon 470uf 35v kf c440 don't know if these are known to be junk or not i don't think its the power supply how do you test the voltage regulators on the logic card do you just take them out of circuit and see if they are bridged

You might want to supply some photos of your power board. We have to see what your seeing. And don't treat your responses like one continuous text message.

[printone2]

Re: Dell 1905FP Powers on then black

Can you check the voltage regulators on the logic card?
Al.

I have learned a few things since I last opened up the panel. I am getting 5v and 10 volts on the voltage regulator. I have ordered new caps for the image card and the IPS, but they will not arrive for a few days. Anything else I can test before hand?

[alexanna]

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.

I am trying to review things. The monitor will power on and we see a 2 second to black problem .The 5 volts stays constant to the logic board. We see a good backlight on signal when the backlights are on, but when the backlights go off the backlight on signal goes to a low voltage, and no image is visible at any time when a bright light is shined at the LCD screen.
To me it is looking like logic board is not recognizing a valid video signal. I do not think you are measuring the voltage regulators correctly.
If my interpretation of you problem is correct and the next test we should do is verify proper operation of the voltage regulators, I am going to ask one of the other members to guide you through it.
Al

[retiredcaps]

Re: Dell 1905FP Powers on then black

I am getting 5v and 10 volts on the voltage regulator.

To test a voltage regulator, put your black probe on a ground screw and your red probe on pin 1. Then move the red to pin 2 and finally pin 3.

For a part number like AS1117-33, the 33 indicates an output voltage of 3.3V DC. An AS1117-18 would output 1.8V DC.

Getting 5V probably indicates the incoming voltage. Getting 10V is a very strange number. It could indicate a voltage regulator failing "high".

So list, measure, and report the results here.

[printone2]

Re: Dell 1905FP Powers on then black

To test a voltage regulator, put your black probe on a ground screw and your red probe on pin 1. Then move the red to pin 2 and finally pin 3.

For a part number like AS1117-33, the 33 indicates an output voltage of 3.3V DC. An AS1117-18 would output 1.8V DC.

Getting 5V probably indicates the incoming voltage. Getting 10V is a very strange number. It could indicate a voltage regulator failing "high".

So list, measure, and report the results here.

I changed to another DMM and get 0 VDC, 3.3VDC and 5.2VDC. The readings do not change if the panel is plugged in or plugged in with the mains on and the lamps lit. Even after the lamps shut off the readings are the same.
Thanks.

[printone2]

Re: Dell 1905FP Powers on then black

To test a voltage regulator, put your black probe on a ground screw and your red probe on pin 1. Then move the red to pin 2 and finally pin 3.

For a part number like AS1117-33, the 33 indicates an output voltage of 3.3V DC. An AS1117-18 would output 1.8V DC.

Getting 5V probably indicates the incoming voltage. Getting 10V is a very strange number. It could indicate a voltage regulator failing "high".

So list, measure, and report the results here.

I changed to another DMM and get 0 VDC, 3.3VDC and 5.2VDC. The readings do not change if the panel is plugged in or plugged in with the mains on and the lamps lit. Even after the lamps shut off the readings are the same.

The voltage regulator is AC 1084-33 0547GL.
Thanks.

[retiredcaps]

Re: Dell 1905FP Powers on then black

I changed to another DMM and get 0 VDC, 3.3VDC and 5.2VDC.

The readings for the voltage regulator look fine for part 1084-33. The 0V DC is the adj pin according to the datasheet.