Dell 2000FP Blank screen problem

[Welchs101]

Re: Dell 2000FP Blank screen problem

The "2 seconds to black" only occurred once out of 15 tries and it was the first time i turned it on this morning. I have not seen it any other time even on first tries. Not saying its not "2 seconds to black" it could be but i have seen the 2 seconds to black before and this just did not seem like it.......but i dont rule anything out.

SHould i now remove the transformers or do somethign else?

[PlainBill]

Re: Dell 2000FP Blank screen problem

I measured the pins on the connector CN1. But instead of measuring CN1 i measured the connector pins on the main board which are then tied to the connector CN1 on the inverter board.

Using the pin designation from one of my earlier pics (also included here) i measured the following:
Pins 8,7,6: Off=>19.83V, On=>19.75V

Pins 5,4,3: Off=>0V , On=>0.002V

Pin2: Off=> 1.963V , On=> 1.971V

Pin1: Off=>0V, On=>3.279V



Note: Not sure if this is significant or not but the very first time i turned monitor on when measuring pin8 i actually saw an image for a split second and then it went away.

That looks like the control signal is working. I believe you are numbering backwards. I saw what appeared to be a number 1 by the right hand pin.

That 'image for a split second' is significant. There is a vast difference between troubleshooting 'dead backlights' and 'two seconds to black' problems.

PlainBill

[Welchs101]

Re: Dell 2000FP Blank screen problem

I measured the pins on the connector CN1. But instead of measuring CN1 i measured the connector pins on the main board which are then tied to the connector CN1 on the inverter board.

Using the pin designation from one of my earlier pics (also included here) i measured the following:
Pins 8,7,6: Off=>19.83V, On=>19.75V

Pins 5,4,3: Off=>0V , On=>0.002V

Pin2: Off=> 1.963V , On=> 1.971V

Pin1: Off=>0V, On=>3.279V



Note: Not sure if this is significant or not but the very first time i turned monitor on when measuring pin8 i actually saw an image for a split second and then it went away.

[PlainBill]

Re: Dell 2000FP Blank screen problem

I measured the resistance of the Q5, Q6 and Q12,Q13 transistors. See data below. See enclosed pic for reference.

Q5:
Pin1-Pin2: 3.86MegOhm
Pin1-Pin3: 3.9MegOhm
Pin2-Pin3: 6kOhm (note: black lead pin2, red lead pin3)


Q6:
Pin1-Pin2: 3.89MegOhm
Pin1-Pin3: 3.89MegOhm
Pin2-Pin3: 5.83kOhm (note: black lead pin2, red lead pin3)

Q12:
Pin1-Pin2: 3.89MegOhm
Pin1-Pin3: 3.84MegOhm
Pin2-Pin3: 5.78kOhm (note: black lead pin2, red lead pin3)


Q13:
Pin1-Pin2: 3.88MegOhm
Pin1-Pin3: 3.84MegOhm
Pin2-Pin3: 5.75kOhm (note: black lead pin2, red lead pin3)

OK, those aren't shorted.

On the inverter, CN1, pins 7 and 8 are the brightness control and On/Off. See if those change state when you push the power button.

PlainBill

[Welchs101]

Re: Dell 2000FP Blank screen problem

I measured the resistance of the Q5, Q6 and Q12,Q13 transistors. See data below. See enclosed pic for reference.

Q5:
Pin1-Pin2: 3.86MegOhm
Pin1-Pin3: 3.9MegOhm
Pin2-Pin3: 6kOhm (note: black lead pin2, red lead pin3)


Q6:
Pin1-Pin2: 3.89MegOhm
Pin1-Pin3: 3.89MegOhm
Pin2-Pin3: 5.83kOhm (note: black lead pin2, red lead pin3)

Q12:
Pin1-Pin2: 3.89MegOhm
Pin1-Pin3: 3.84MegOhm
Pin2-Pin3: 5.78kOhm (note: black lead pin2, red lead pin3)


Q13:
Pin1-Pin2: 3.88MegOhm
Pin1-Pin3: 3.84MegOhm
Pin2-Pin3: 5.75kOhm (note: black lead pin2, red lead pin3)

[PlainBill]

Re: Dell 2000FP Blank screen problem

I checked the fuse......its a short measures about 0.2 or 0.3ohm.

For the transistors. Any idea if they are mosfets or bi-polars? Any idea on data sheet? Or if you want i can measure resistances and diode-checks across all leads. Would this suffice?

Note: Transistors have marking of DT and QX on them.

They are bipolar transistors. This is the same circuit used in the Dell 1703 monitors. Just check the resistance between each set of pins. For Q5 and Q6 measure from the pin on the upper left to the pin on the right. Then measure from the upper left to the lower left. Then measure from the lower left to the pin on the right. If a transistor is shorted it will read less than 10 ohms.

PlainBill

[Welchs101]

Re: Dell 2000FP Blank screen problem

I checked the fuse......its a short measures about 0.2 or 0.3ohm.

For the transistors. Any idea if they are mosfets or bi-polars? Any idea on data sheet? Or if you want i can measure resistances and diode-checks across all leads. Would this suffice?

Note: Transistors have marking of DT and QX on them.

[Dgtech]

Re: Dell 2000FP Blank screen problem

I had a 15 inch Dell monitor that was laid out just like this one. There is a surface mount fuse on the inverter board (F1 near the white connector) that may be blown.

[PlainBill]

Re: Dell 2000FP Blank screen problem

Rather than resolder the transformers at this point, there are a couple of things to do first.

1. Check the fuse

2. Check Q5, Q6, Q13 and it's companion, (probably Q12) to see if any are shorted.

3. If no transistors are shorted, remove one of the transformers and repeat the measurements. I would prefer measurements in this pattern

1 to 2, 1 to 3, 1 to 4, 1 to 5, 1 to 6, 1 to 7, 1 to 8, 1 to 9, 1 to 10, 1 to 11

2 to 3, 2 to 4, 2 to 5, 2 to 6, 2 to 7, 2 to 8, 2 to 9, 2 to 10, 2 to 11

3 to 4, 3 to 5, 3 to 6, etc

4 to 5, 4 to 6, etc

5 to 6, etc

etc,

etc until finally

9 to 10, 9 to 11

10 to 11

For this purpose 3.88 Mohms is essentially open. Just say 'open' or use a dash (-) for anything over 100Kohm.

What I would expect to see is the pins on the primary side appear connected in pairs, perhaps 1 to 7, 2 to 3, 5 to 6. On the secondary side I would expect to see two pairs.

4. A picture of the back of the inverter board.

PlainBill

[Welchs101]

Hi,

I have a Dell 2000FP LCD monitor.

Problem description:
When i power up the monitor the green led comes on and stays on but there is no picture shown.

I am enclosing pictures of the boards (see enclosed pics).
Overall => Shows both inverter board and main board

Inverter_Pic=>Shows pic of inverter. Shows pad numbering for transformers. Note: I think pad1 of transformer is denoted by "yellow" dot.

Mag_Invert_1=>Close up of left side of inverter
Mag_Invert_2=>Close up of middle of inverter
Mag_Invert_3=>Close up of right side of inverter




What i have done thus far:
1-With the power on i shine a flash-light onto the screen. I can see a faint image. So this tells me from past experience that its probably either the bulbs or inverter board.

2-I checked each of the 6 bulbs with my "home-made" bulb tester. They all appear to be "good" bulbs.

3-I also measured the transformer using DVM:
Note: Transformer was "in-circuit" for these measurements.

Transformer A:
Pin1_to_Pin8: 3.88Mohm
Pin1_to_Pin9: 3.88Mohm
Pin1_to_Pin10: 3.88Mohm
Pin1_to_Pin11: 3.88Mohm
Pin2_to_Pin8: 6.15Kohm
Pin2_to_Pin9: 6.15Kohm
Pin2_to_Pin10: 6.15Kohm
Pin2_to_Pin11: 6.15Kohm
Pin3_to_Pin8: 6.13Kohm
Pin3_to_Pin9: 6.13Kohm
Pin3_to_Pin10: 6.13Kohm
Pin3_to_Pin11: 6.13Kohm
Pin4_to_Pin8: 6.11Kohm
Pin4_to_Pin9: 6.11Kohm
Pin4_to_Pin10: 6.11Kohm
Pin4_to_Pin11: 6.11Kohm
Pin5_to_Pin8: 6.08Kohm
Pin5_to_Pin9: 6.08Kohm
Pin5_to_Pin10: 6.08Kohm
Pin5_to_Pin11: 6.08Kohm
Pin6_to_Pin8: 3.84Mohm
Pin6_to_Pin9: 3.84Mohm
Pin6_to_Pin10: 3.84Mohm
Pin6_to_Pin11: 3.84Mohm
Pin7_to_Pin8: 199.2ohm
Pin7_to_Pin9: 199.2ohm
Pin7_to_Pin10: 199.2ohm
Pin7_to_Pin11: 199.2ohm


Transformer B:
Pin1_to_Pin8: Open
Pin1_to_Pin9: Open
Pin1_to_Pin10: Open
Pin1_to_Pin11: 3.8Mohm
Pin2_to_Pin8: Open
Pin2_to_Pin9: Open
Pin2_to_Pin10: Open
Pin2_to_Pin11: 5.91Kohm
Pin3_to_Pin8: Open
Pin3_to_Pin9: Open
Pin3_to_Pin10: Open
Pin3_to_Pin11: 5.11Kohm
Pin4_to_Pin8: Open
Pin4_to_Pin9: Open
Pin4_to_Pin10: Open
Pin4_to_Pin11: 5.91Kohm
Pin5_to_Pin8: Open
Pin5_to_Pin9: Open
Pin5_to_Pin10: Open
Pin5_to_Pin11: 5.88kOhm
Pin6_to_Pin8: Open
Pin6_to_Pin9: Open
Pin6_to_Pin10: Open
Pin6_to_Pin11: 3.8Mohm
Pin7_to_Pin8: Open
Pin7_to_Pin9: Open
Pin7_to_Pin10: Open
Pin7_to_Pin11: 199.2ohm


NOte: If there is a better way to show this data in a tabular format let me know.




4-I also measure the voltages present on the connector.
Pin8: 19.75V
Pin7: 19.75V
Pin6:19.75V
Pin5: 0V
Pin4: 0V
Pin3: 0V
Pin2: 1.972V
Pin1: 3.279V




Basically i would like some input on what to try/do next. From above is the transformer "bad"? Also, any inputs / suggestions you can give please let me know.

NOte: I was planning to re-solder the transformer connections but i wanted to post what i have done thus far.