Dell 1704FPT

[Loupe]

Re: Dell 1704FPT

Hi budm,

Sorry to be so novice in electronics.

I improved a little bit my knowledge about the SMPS.
I understand the basic difference between linear PS and Switch mode PS.
I better figure out the components function on the primary side than in the secondary side on the board.
I guess you wanted to enlighten me to the possibility of a short-circuit in one of the rectifiers in the secondary (1 SB1060FCT & 2 ER1002FCT) side that could create an excessive load signal to the feed back pin (via an activation of the opto-coupler and a precision Zener Diode circuit ) of the PWM controller (SG6841).
So that the oscillating voltage value on the 5V and 12V outputs could be the result of a cyclical shut down and turn on of the oscillating signal to the power transistor (FQPF8N60C) from the PWM controller.
So my first question how could I test the 3 rectifiers on the secondary side ?

By small lytics start-up/running cap on the primary side do you mean those encircled on the new posted pics ?

I hope you'll have some time to consider my message.

[Loupe]

Re: Dell 1704FPT

I replaced the 11 caps surrounded in the attached pic.

"So you did not replace the small lytics start-up/running cap in the primary side?"

Which one do you mean on the picture ?

"The rectifiers in the secondary side are all OK?"

Where are they located on the board ? And how to test them ?

Thanks for your help.

[budm]

Re: Dell 1704FPT

So you did not replace the small lytics start-up/running cap in the primary side?
The rectifiers in the secondary side are all OK?

[Loupe]

Re: Dell 1704FPT

Hi, I read all above posts concerning this thread, but didn't find answer to my problem.
I had some trouble to switch on my Dell 1704 FPTt monitor. The greenlight from the front panel remained faded.
Changing all caps on the low voltage side of the power board helped solved the problem for a while until a recent grid power failure.
I measured the voltage at several points on the board and noticed that the + 5 V leads from the power board to power on the video control board were not stabilized (the value oscillated from 0 to 3 or 5 Volts with the DMM.
So I tried to find out the start of this failure.
I noticed this oscillating values on the leads of a component located at the limit between HV/LV separation, but I'm not sure that's the source of the problem.
This IC component is a 4 pin tagged I802 on the board and labeled Lo 503 817D x ; but I don't know what kind of component it is.
[It looks like a Transistor Output Optocoupler, Through Hole, 4-Pin DIP]
It is located on top middle of the picture :
https://www.badcaps.net/forum/attach...8&d=1265184429
(the first picture of this thread)
Your help would be much appreciated.

[flinx]

Re: Dell 1704FPT

reviving an old post.

I have a couple of these monitors. one of them had the 2 seconds on then off. I connected the CCFL on each side to one or the other connectors on the power supply and noted that one side of the high voltage output was not working.

All caps appeared ok, I did some checking and troubleshooting but could not nail down the problem. I did note a slight difference on the High voltage transformer (from the side that was not working) as compared to the ohms readings of the HV PS on another board. I replaced the HV transformer and the problem went away.

Even though none of the capxon caps showed signs of bulging or leaking I replaced all the electrolytic caps on the board (except the large one). I replaced them after I noted the display was working properly.

Capxon capacitors are junk.

[selldoor]

Re: Dell 1704FPT

Dell did not do many schematics for monitors (at least showing the power board)
Problem is usually bad solder. bad inverter transformer - test see here
https://www.badcaps.net/forum/showpo...04&postcount=8
IF your board is the same.
Bad bulbs - perhaps you can test those in your recently fixed monitor.
Bad inverter mosfets - usually 5707s (or similar) on the back of the board.
We also have a useful guide on 2 seconds to black by retiredcaps
https://www.badcaps.net/forum/showthread.php?t=10419
Start at post19.

[fc227a]

Re: Dell 1704FPT

I know this is an old thread, but I have a question. IS there a schematic for this board?

[selldoor]

Re: Dell 1704FPT

Hi - When you say no video have you checked with a flashlight on the screen at an angle - assumes you have a source connected.

Welcome to the forum-

We can often help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back (in the same orientation) and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed

https://www.badcaps.net/forum/attach...7&d=1280167246

https://www.badcaps.net/forum/attach...6&d=1280167246

https://www.badcaps.net/forum/attach...4&d=1280167246

[bananaman]

Re: Dell 1704FPT

Gentlemen:

I was asked to fix a dell 1704FTP monitor. When powered up the green light comes on and is steady. There is not any video, not even for a few seconds (2 second to death issue is not applicable) I disassembled and the power supply board looks fine. Caps are not expanded and R125 looks fine. The only thing I noted was a funny bubble on the side of a blue trimmer (VR801 I think), but not sure that is a problem.

I think may be a video problem. There was a screw missing that tells me it was opened before. Anyone have similar problem? (solid green power light with no video at all)

Thanks

bananaman

[pcarbery]

Re: Dell 1704FPT

Things happen slowly in my country....anyway, I finally fixed the monitor and am looking at it right now. In the end, I purchased a new inverter board on ebay for 20 bucks. I couldn't locate any bad caps (but are sure there were some) I took a chance that the lights were ok and went ahead with the purchase. I will post again if there is any problem with it. So far so good, but it has only been switched on for 1 hour.
Thanks for all the help everyone.

[budm]

Re: Dell 1704FPT

You can get one of these for testing your lamps:
http://www.ebay.com/itm/1pc-4-Lamp-B...ht_3916wt_1400

http://www.ebay.com/itm/LCD-Monitor-...ht_1794wt_1400

[pcarbery]

Re: Dell 1704FPT

thanks guys for the replies.....will test lamp and reply back in a few days

[Rtech]

Re: Dell 1704FPT

Could still be either !! you really need a test Backlight to identify where it is.

[budm]

Re: Dell 1704FPT

Try test lamp?
https://www.badcaps.net/forum/showthread.php?t=19987

[pcarbery]

Re: Dell 1704FPT

Thanks Rtech, does you reply mean that it is one of the lights or could it still be the inverter board?

[Rtech]

Re: Dell 1704FPT

hi Rtech, sorry for the late reply but couldnt get back to this project until now. Resistances of the secondaries are fine. A = 459 , B=434. all cap's look ok, no signs of any problems......will check them with DMM when I get a different one that can check farads. (I think I have one in work somewhere).
By the way, I can see the screen when I shine a flashlight on to it.

If you can see the image,,then definitely a Backlight issue.

[pcarbery]

Re: Dell 1704FPT

hi Rtech, sorry for the late reply but couldnt get back to this project until now. Resistances of the secondaries are fine. A = 459 , B=434. all cap's look ok, no signs of any problems......will check them with DMM when I get a different one that can check farads. (I think I have one in work somewhere).
By the way, I can see the screen when I shine a flashlight on to it.

[Rtech]

Re: Dell 1704FPT

It may be the transformer that has failed ?? have you checked the Resistance of the secondaries ??

[pcarbery]

Re: Dell 1704FPT

Hi there all,

I know this is an old discussion, but it is the best I have found; and hope some of you might be able to help.
I am wondering if anyone has resolved this issue. I too have one of these Dell monitors that displays a screen for less than a second before going blank. I too have noticed a burnt R125 resistor (but still seems intact). I was thinking of replacing the inverter board but am reluctant to, if it is just going to fail again.

I suspect from reading other forums that one of the lights may be gone and that the board automatically shuts down all others once it senses this....perhaps this is why the R125 resistor is overheating.

Any help? ideas?

[ralphup]

Re: Dell 1704FPT

Many thanks

Hello there, I have sent you a PM and await your response sir!