Has the Dell 1800FP exhibited bad caps?

[Bobdee]

Re: Has the Dell 1800FP exhibited bad caps?

I have the same problem as gyeap. My backlight works no problem. It is just the the screen turns on and on for a second with VGA and HDMI. My BLON flickers with the LCD. So the logic board is the issue. Was your problem a cap on the power supply or a problem with the logic board?

Just a suggestion if I may
Resolder the two dual rectifiers on the heatsink they are known to be problem and check the solder joints on the power supply as well and see how that goes first

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

But if i a geeting the right voltages at the output of the PS should all those be correct.

[Bobdee]

Re: Has the Dell 1800FP exhibited bad caps?

But if i a geeting the right voltages at the output of the PS should all those be correct.

ARE you getting steady and correct outputs from the p/supply when the Blon flickers, (the rectifier solder joints are usually bad on this p/s) they are worthy of a check anyway

[kc8adu]

Re: Has the Dell 1800FP exhibited bad caps?

solder the rectifiers now or be sorry when the ice2as01 dies.

[Krankshaft]

Re: Has the Dell 1800FP exhibited bad caps?

For future reference here is where you can pickup the ICE PWM IC.

http://www.bluestar-online.com/ICE2A...FeFM5QodKzei2Q

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

Yes the voltages is steady. It might fluctuate 0.1V. I will resolder the rectifier. Just for clarification. They are the two TO220 packaged devices against the heat sink. And when you say bad, do you just mean cold solder joints?

[gyeap]

Re: Has the Dell 1800FP exhibited bad caps?

drewcam888,

I have not been able to fix my monitor yet. On the entire logic board, only C739 measured bad ESR. I soldered a good capacitor in parallel to it but it did not help at all. The other cap with the second worst ESR is C207. I did the same and also did not solved the problem. I ran out of ideas and the unit is now collecting dust.

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

I have also done the caps on c207 and c739 and they didnt help

[Krankshaft]

Re: Has the Dell 1800FP exhibited bad caps?

Am I the only one not looking at the inverter?

It looks to be external of the power supply and a backlight that comes on and shuts off is almost always either bad inverter driver transistors in rare cases an inverter transformer. Or bad CCFLs causing the inverter to shut down.

[gyeap]

Re: Has the Dell 1800FP exhibited bad caps?

Krankshaft,

For my unit, I have looked into the inverter. It can stay on for ever if no video signal is applied. With video signal applied, it randomly turns on/off at about 0.5 - 3 seconds interval. Perhaps it has problem synchronizing the video signal and decided to blank it. But when it turned on, the image is good.

I thought of a hack to force the BLON signal to high/low with a resistor. This should force the backlight to always turned on regardless of the logic board's command. I have not tried this yet.

[PlainBill]

Re: Has the Dell 1800FP exhibited bad caps?

Krankshaft,

For my unit, I have looked into the inverter. It can stay on for ever if no video signal is applied. With video signal applied, it randomly turns on/off at about 0.5 - 3 seconds interval. Perhaps it has problem synchronizing the video signal and decided to blank it. But when it turned on, the image is good.

I thought of a hack to force the BLON signal to high/low with a resistor. This should force the backlight to always turned on regardless of the logic board's command. I have not tried this yet.

This sounds like a problem with the logic card. Did you check the ESR of the caps on it?

PlainBill

[Bobdee]

Re: Has the Dell 1800FP exhibited bad caps?

Yes the voltages is steady. It might fluctuate 0.1V. I will resolder the rectifier. Just for clarification. They are the two TO220 packaged devices against the heat sink. And when you say bad, do you just mean cold solder joints?

What I meant was steady under load.
Also my joints were so bad on the Rectifiers that it was obvious that on there last legs of life they had to have been arcing to make any connection,
They took out the PWM controller + the Mosfet on H/sink + Current sense resistor + and possibly the main transformer (need a ring tester to test it to be sure) still on back burner

[kc8adu]

Re: Has the Dell 1800FP exhibited bad caps?

i have been seeing these and other lg units with the same psu coming in with all the lytics on the psu high esr.just had one from a neighbor that looked like you were watching through a screendoor.and it would blink.all the caps on this board were bad.ecxept for the primary which was nichicon.all the rest were samwha.
heat is the issue.

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

I know the inverter is ok because I can keep the BLON at 5Vdc and it is on constantly. The video will just blink. It works fine without a video signal connected. My solder joints on the rectifiers look great.

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

I could replace all the caps on the PS but I really think it is a logic board problem. Because the screen is ok without a video input. I am hoping it isnt a corrupt IC on the logic board.

[Bobdee]

Re: Has the Dell 1800FP exhibited bad caps?

I could replace all the caps on the PS but I really think it is a logic board problem. Because the screen is ok without a video input. I am hoping it isnt a corrupt IC on the logic board.

Sounds like a recap on the vid/board
Just out of curiosity try turning it on without a VGA connected to it,
And then connect a VGA to it, with the other end of the VGA NOT connected to anything else and see if you get same symptoms as if it was connected to a Computer

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

Yes the monitor is ok with a vga connected to monitor and not pc. It puts the monitor in power saving mode and it turns off.

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

I really need an ESR meter now. It would make finding these bad cap so much easier.

[drewcam888]

Re: Has the Dell 1800FP exhibited bad caps?

I was able to use an external supply for one voltage. I then used the internal for the other voltages. I then switched voltage for each supply. This generated the same flickering as before. This leads me to think the logic is bad. Is this correct? Or do you think I would have to have both voltages on external supply to rule the PS out.

[PlainBill]

Re: Has the Dell 1800FP exhibited bad caps?

I was able to use an external supply for one voltage. I then used the internal for the other voltages. I then switched voltage for each supply. This generated the same flickering as before. This leads me to think the logic is bad. Is this correct? Or do you think I would have to have both voltages on external supply to rule the PS out.

Most LCD displays I've repaired have a power supply with 5V and 12V outputs. The 5V supply is used by the logic card and the display panel. The 12V supply is used by the inverter (often on the power supply board).

Depending on the design, the logic board may generate two or three additional voltages. These are provided by on-board bucking regulators. A bad cap filtering any of those voltages could cause the problems you describe. An ESR meter would be one way to troubleshoot; pulling the caps and checking the capacitance might identify the problem. Looking at the bucking regulator outputs with a good scope may also provide a clue.

I would also raise the ugly specter that it might be a problem with the control chip on the logic board, it's support components, or even the display panel itself.

PlainBill