Dell 1704FPT

[jonny800]

I recently received a Dell 1704FPT from a friend. The monitor will power up and for a second the backlighting is on. Then the backlight will turn off. If you shine a light over it you can see it is still displaying an image. Also the power LED stays green the entire time.

Looking at the capacitors I can't see any real issues. The capacitors are a mix of CapXon and Su'scon. It's my first time trying to fix an issue with a monitor so I'm just looking for ideas of how to fix it.

So I guess a question is should I just replace the some or all the capacitors? Or from my description of the problem could there be a different issue?
Any information would be appreciated.

[PlainBill]

Re: Dell 1704FPT

I recently received a Dell 1704FPT from a friend. The monitor will power up and for a second the backlighting is on. Then the backlight will turn off. If you shine a light over it you can see it is still displaying an image. Also the power LED stays green the entire time.

Looking at the capacitors I can't see any real issues. The capacitors are a mix of CapXon and Su'scon. It's my first time trying to fix an issue with a monitor so I'm just looking for ideas of how to fix it.

So I guess a question is should I just replace the some or all the capacitors? Or from my description of the problem could there be a different issue?
Any information would be appreciated.

You describe the 'two seconds to black' problem. The backlight controller is sensing a fault and shutting down the backlights. A good picture of the back side of the board would help us point out a few spots to begin testing.

PlainBill

[Krankshaft]

Re: Dell 1704FPT

From the top pics of the board test the 4 circled transistors for shorts 2SC5707s no doubt.

Use the diode check function of the DMM to test if you don't have one get one it will be a very important tool for troubleshooting.

What's with the DC jack and the AC socket? It can run off both AC and DC that seems weird.

The only reason I can think of to run it off DC is if it was designed for 12V auto use.

[ecking767]

Re: Dell 1704FPT

From the top pics of the board test the 4 circled transistors for shorts 2SC5707s no doubt.

I have this same board and the output transistors are MOSFET N-CHANNEL CED13N07 OR Sometime this board may have AOU402.

http://www.alldatasheet.com/view.jsp...hword=CED13N07

You don't want to install 2SC5707 Transistor in place of an MOSFET

The inverter I.C. CHIPS should be OZ9930 or Its may read OZRRAG Which is that same.

Hope this help

[Krankshaft]

Re: Dell 1704FPT

Wow a Dell without C5707s shocking!

Ok threw me off balance there. Should have known something was wrong when the metal film caps between the drivers was missing.

Use the diode check on the DMM measure from gate to source flip probes. Should only get a reading in one direction. Do the same from gate to drain.

Use the datasheet provided by Ecking767 to identify the pinout.

Check out all four FETs this way.

Common backlight shutdown driver transistor is shorted one CCFL doesn't come on PWM protection senses it and shuts whole inverter down. The light is so well diffused across the screen it's hard to notice one CCFL not firing on the LCD in the few seconds it's on.

[jonny800]

Re: Dell 1704FPT

Ok, here is the picture that was requested. Also the jack on the board is for the power for the add-on speakers.

I will also do the diode check and let you know what I find out.

[jonny800]

Re: Dell 1704FPT

Ok, I did the test. I only got a reading when I went from the drain to the source. Three of them read 002 and one read 001.

[PlainBill]

Re: Dell 1704FPT

Ok, here is the picture that was requested. Also the jack on the board is for the power for the add-on speakers.

I will also do the diode check and let you know what I find out.

Good picture. With power off, measure the resistance between the pair of points labeled A, and again between the pair labeled B. They should be very close. This will catch an open secondary, and maybe a shorted secondary.

This next step is more difficult. Reassemble the monitor enough that you can power it up with the CCFLs hooked up. It helps if you have a second person to handle the power button on the monitor. The voltages at certain points on the power supply / inverter are high enough to give you a nasty shock.

Set your DMM to the AC volts range. The voltages you will be measuring should be under 10 volts, but if there is a problem they could be over 700 VAC, so I suggest starting at the highest range possible and going to lower ranges once you establish the voltage is in a safe range. Connect the black lead of the DMM to ground. The broad trace that runs the width of the card at the top of the picture is ground. I have labeled six additional points on the board. It may be helpful if you locate the same points on the top side of the board, as well as the ground point.

The points labeled R1 through R4 are the return lines for the CCFLs. The voltage on those lines should be less than 10 VAC. If one reads zero, there is a problem with the CCFL, the transformer, or the wiring to the CCFL. The points labeled RF and CF are the feedback lines from the transformer outputs.

The test process goes like this. Plug in the monitor, set the DMM to the highest AC voltage range (700 volts). Touch the black lead to ground, touch the red lead to a test point, have your assistant push the power button on the monitor until it turns green. If the meter doesn't show any reading, reduce the range to 200 volts and repeat, and again to the 20 volt range and repeat.

Repeat this for the remaining test points. Report the results.

If it isn't obvious, we are looking for a return line that reads 0 volts, or a feedback line that reads either 0 volts or a high voltage.

PlainBill

[jonny800]

Re: Dell 1704FPT

Ok PlainBill I did the test and have the results for you. Also to note when I turned on the monitor the LCD lit up and stayed on but was flickering.

A = 457
B = 454

Also my DMMs lowest AC voltage range is 200. R1 and R3 were jumping all over the place.

CF = 0.4
RF = 0.1
R1 = 98.9 to 10.6
R2 = 0
R3 = 8.5 to 9.6
R4 = 0

Do you need me to get a DMM with a lower AC voltage range or will that information work?

Thanks for your help.

[PlainBill]

Re: Dell 1704FPT

Ok PlainBill I did the test and have the results for you. Also to note when I turned on the monitor the LCD lit up and stayed on but was flickering.

A = 457
B = 454

Also my DMMs lowest AC voltage range is 200. R1 and R3 were jumping all over the place.

CF = 0.4
RF = 0.1
R1 = 98.9 to 10.6
R2 = 0
R3 = 8.5 to 9.6
R4 = 0

Do you need me to get a DMM with a lower AC voltage range or will that information work?

Thanks for your help.

That information helps, but still leaves me with questions.

The resistances indicate there is no transformer problem. I'm not sure about CF and RF readings, I don't have a lot of experience with this design.

I assume R1 was 9.9 to 10.6, not 98.9?

The fact that TWO return lines were 0 doesn't make a lot of sense. One would indicate either a bad CCFL, or a shorted diode. Two of them???

I'm going to have to think about this. PM me if I haven't updated this by 2-09.

PlainBill

[dalbrech]

Re: Dell 1704FPT

Jonny800,

Did you ever resolve the problem with you Dell 1704FPT monitor? The reason I ask is I have the same monitor with the same problem. I was planning on replacing the inverter/power board but now it seems the problem could also be a bad lamp?

Thanks,

Dave Albrecht

[captainmorgan04]

Re: Dell 1704FPT

Hi all

Has anyone had any problems with the resistor at location R125 blowing out. I was given to monitors and both have the same resistor blown out. If you know this resistor and a direct link to where I can buy them Please let me know. You can Email me At Clvnmorgan836@gmail.com...Thanks

[jkleslie]

Re: Dell 1704FPT

Hi all

Has anyone had any problems with the resistor at location R125 blowing out. I was given to monitors and both have the same resistor blown out. If you know this resistor and a direct link to where I can buy them Please let me know. You can Email me At Clvnmorgan836@gmail.com...Thanks

Same here! I just need to confirm the color bands on R125 (mine was burnt beyond recognition). Is it red, black, blue and gold...or is that red, black, green and gold?

[captainmorgan04]

Re: Dell 1704FPT

Same here! I just need to confirm the color bands on R125 (mine was burnt beyond recognition). Is it red, black, blue and gold...or is that red, black, green and gold?

Red is 2 Black is 0 green is 5 (0's) and gold is +-5%

2000000 ohm

I'm taking Automotive electronics this semester and that is what the book values are.Hope this helps cause I took one out of the other monitor to try and the backlight comes on but goes back off. All caps look good. What ever burned up the resistor must have done other damage that I can't see. I may try buying a new board that I've seen for $30 on the net. Good Luck.

[retiredcaps]

Re: Dell 1704FPT

I may try buying a new board that I've seen for $30 on the net.

I don't know where you live, but I can get an used 19 inch LCD monitor for $20 if I'm patient. I can easily get an used 17 inch LCD monitor for $30 almost anytime.

$30 for a new board seems like a lot.

[Lumberjack777]

Re: Dell 1704FPT

Hi all

Has anyone had any problems with the resistor at location R125 blowing out. I was given to monitors and both have the same resistor blown out. If you know this resistor and a direct link to where I can buy them Please let me know. You can Email me At Clvnmorgan836@gmail.com...Thanks

Same here! I just need to confirm the color bands on R125 (mine was burnt beyond recognition). Is it red, black, blue and gold...or is that red, black, green and gold?

I bought this same Dell 1704FPT at an electronics recycling shop for 5 bucks. The first thing I noticed was the resistor at R125 was almost fried. It still tested to be good. But it had fried so much the copper track had partially come off. I soldered a bridge, but it still didn't fire up. So I ordered a new power/inverter board and it did work. For about 6 hours. Then the backlights went off again. Upon inspection I noticed the same heat brown spots at R125. This resistor and board were fine before I installed it and plugged it in.

So my question is. What causes that resistor at R125 to fry in so many boards? Is this a design issue? Or maybe a bad CCFL? Can a bad CCFL do this? You can look at Plain Bill's picture to see the problem we are dealing with. It's labeled RF in red in his picture.

The company has sent me a new board (for free) and I think I better resolve this issue before I plug in the new board. I don't want this one to fry too.

Thank you

[cidi1484]

Re: Dell 1704FPT

Oh boy - I had 11 monitors dumped on me today all having this exact same problem. Please tell me someone has tracked down the root of the issue? Otherwise I will be buried for some time trying to figure it out.

I also have a few that wont even power on. Since I dont usually fix this brand (since Dell usually covered it) does anyone have any quick hitters for dells that wont power on?

Thanks for your help in advance!

[retiredcaps]

Re: Dell 1704FPT

all having this exact same problem.

1) What is "this exact same problem"?

2) If you have 11 of these and would like help, please post clear focused pictures using the manage attachments function of your boards (top down view). We don't need pictures of all 11, just 1 of the lcds will be fine. Please do not post inline.

3) Do you have a multimeter?

[UniT3d]

Re: Dell 1704FPT

Excuse me guys,

I have this exact board on a dell 1704fpt with R125 resistor bands unrecognizable (burnt and took the track off with it). Can anyone be so kind as to state either the correct value or colors please? It reads 130kOhms on the meter but I don't know if this is correct. The resistor is the only thing left to replace before I fire this lcd up ...

Added:
Whoops ... got it ... R125 is Red Black Green Gold .... powered up and voila, it works ....


Thanks.

[ralphup]

Re: Dell 1704FPT

Hi guys,

bit of a STUPID question (but then my Dad always told me there are no stupid questions....only stupid people!)

I have a DELL 1704 with a cracked CCL and burnt R125, I have just purchased a replacement LCD and I understand from the posts here that I need to replace the R125 with a 2000000 (2 megohm) resistor, but what wattage should I use? also where would be best place in UK to purchase?

THANKS!!