Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Computer Displays
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 10-05-2009, 02:40 PM   #41
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

There are two regulator on my logic board. One is 5 to 3.33 and the other is 12 to 5. Both seem to be ok. I dont have any idea why they go from 12 to 5 when they have 5 already from the PS. 12 is also driven to the LCD driver on the actual screen itself. I really am hoping it isnt a bad main IC on the logic board. I can replace any other IC as long as no reprogramming is needed.

Last edited by drewcam888; 10-05-2009 at 02:45 PM..
drewcam888 is offline   Reply With Quote
Old 10-05-2009, 04:03 PM   #42
PlainBill
Badcaps Veteran
 
PlainBill's Avatar
 
Join Date: Feb 2009
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist
Posts: 7,013
Default Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by drewcam888
There are two regulator on my logic board. One is 5 to 3.33 and the other is 12 to 5. Both seem to be ok. I dont have any idea why they go from 12 to 5 when they have 5 already from the PS. 12 is also driven to the LCD driver on the actual screen itself. I really am hoping it isnt a bad main IC on the logic board. I can replace any other IC as long as no reprogramming is needed.
What is the main IC on the logic board? Have you checked the datasheet? Agree, it is strange that they have two separate 5 volt supplies.

Looking at the picture of the logic board somone posted, it looks like there may be THREE bucking regulators on the logic board.

There may be another option. Someone is selling the controller on eBay. Double check to make sure this is the proper part; at the price you can't spend too much time troubleshooting yours. http://cgi.ebay.com/1800FP-DELL-LCD-...d=p3286.c0.m14

Maybe not. That looks like it may be the lcd controller.

PlainBill
__________________
For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

Last edited by PlainBill; 10-05-2009 at 04:08 PM..
PlainBill is offline   Reply With Quote
Old 10-05-2009, 05:07 PM   #43
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

There is a third regulator. It is the SOT-223 part. And it is really wierd. The output is 2.5V and the input i think is 5V. But I cant find where the input gets to the input of the regulator. And the output doesnt appear to be connected to anything. It is only a 2 layer board so this should be easy. Maybe I am blind. I can find logic board for like 25 but i am determined to fix this one.
drewcam888 is offline   Reply With Quote
Old 10-05-2009, 10:09 PM   #44
PlainBill
Badcaps Veteran
 
PlainBill's Avatar
 
Join Date: Feb 2009
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist
Posts: 7,013
Default Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by drewcam888
There is a third regulator. It is the SOT-223 part. And it is really wierd. The output is 2.5V and the input i think is 5V. But I cant find where the input gets to the input of the regulator. And the output doesnt appear to be connected to anything. It is only a 2 layer board so this should be easy. Maybe I am blind. I can find logic board for like 25 but i am determined to fix this one.
Again, try to get the datasheets for the two large ICs. One or both of them require 2.5. The fact you can't determine where the output goes may be significant - check for solder joint.

PlainBill
PlainBill is offline   Reply With Quote
Old 10-06-2009, 06:36 AM   #45
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

Can anyone confirm if this is a multilayer PCB for the logic board? Also does anyone have the schematic for the non BGA version of the logic board. The LG document listed earlier has the newer BGA version schematic.

Last edited by drewcam888; 10-06-2009 at 06:38 AM..
drewcam888 is offline   Reply With Quote
Old 10-06-2009, 10:31 AM   #46
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

The 2.5 is used by one IC and it is getting to the IC. I guess there is an internal power plane.
drewcam888 is offline   Reply With Quote
Old 10-06-2009, 12:02 PM   #47
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

I have parallel or replaced caped all but one capacitot on the logic board. the only one left is the 12V supply 470uf capacitor which i dont have a replacement for and paralleling isnt possible on the bottom of the board. Anyone have any other suggestions
drewcam888 is offline   Reply With Quote
Old 10-12-2009, 07:33 AM   #48
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

Anyone else have any suggestions? I wouldn't think it is a problem with a main IC since it works in screensaver mode and the screen flashes on and off with video connected. To me this flashing wouldn't be a failure mode of the main IC.
drewcam888 is offline   Reply With Quote
Old 10-13-2009, 10:44 AM   #49
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

If no one has any suggestions. Then does anyone have the schematic or manual for the nonBGA logic board.
drewcam888 is offline   Reply With Quote
Old 10-17-2009, 11:59 PM   #50
carcomp
New Member
 
Join Date: Oct 2009
Posts: 4
Default Re: Has the Dell 1800FP exhibited bad caps?

I am working on one of these Dell 1800FP monitors. I'm lucky enough to have two (one that is working and one I am fixing).

For reference: Monitor1 is the good one. Monitor2 is the bad one

The power supply went bad on monitor2. I totally removed the power supply and sourced the power from an ATX power supply. It worked for about 3 months, then the display started flickering (backlight going on and off). It would sometimes work for awhile then start flickering when I had a white screen (like a browser open). Weird huh? Now its always flickering.
...

It does this whether VGA is hooked up or its in self test mode. I thought it was the inverter. FYI, I replaced the caps on the inverter but they were good and that didn't fix the flicker... read on I switched the inverters in the monitors thinking that monitor1 would now exhibit the flashing, but monitor2 was still flashing. That means its not the inverter.

I tried using a variable power supply and bumping the voltage slightly over 5 and 12v (5.10 and 12.10) but the flashing continued.

I'm thinking its the logic board... But I don't really have the skills nor the tools to do logic testing. I'm wanting to know if I can "force" the inverter to just stay on, vs the logic board telling it to turn on.

From what I've read, there is a BLON signal. Can I manipulate this by maybe sourcing voltage from somewhere?

I'd just buy a new board, but I'm laid off now.

I'm searching for a pinout and an explanation of BLON right now...
carcomp is offline   Reply With Quote
Old 10-18-2009, 05:45 AM   #51
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

Jump stick a wire in the 5v out from the power supply and pin 8 of the inverter plug and the backlight will come on.
drewcam888 is offline   Reply With Quote
Old 10-18-2009, 09:24 AM   #52
carcomp
New Member
 
Join Date: Oct 2009
Posts: 4
Default Re: Has the Dell 1800FP exhibited bad caps?

Hmm I checked pin 8. I'm gettin 4.6V there. I tried jumping anyway, but no change. I checked eveything else. I've regulated the voltage so I KNOW its getting 12v and 5v (checked with a meter). I test 12v at the inverter, as well as perfect grounds.

Can I run that inverter completely independent of the logic board? If so, what is PIN 7?

BTW: I'm from indiana too.
carcomp is offline   Reply With Quote
Old 10-18-2009, 11:52 AM   #53
carcomp
New Member
 
Join Date: Oct 2009
Posts: 4
Default Re: Has the Dell 1800FP exhibited bad caps?

Aw cripes, it was underpowered. I had 12v but only 2.5 amps. DOH! I pulled the power supply from the other monitor and poof, it started working. Now I have to find something that will make 12v with more amps.
carcomp is offline   Reply With Quote
Old 10-18-2009, 09:55 PM   #54
carcomp
New Member
 
Join Date: Oct 2009
Posts: 4
Default Re: Has the Dell 1800FP exhibited bad caps?

Gotta love those good ol' AT power supplies.
carcomp is offline   Reply With Quote
Old 10-19-2009, 07:09 AM   #55
drewcam888
EE Nerd
 
Join Date: Oct 2009
City & State: Indiana
Posts: 44
Default Re: Has the Dell 1800FP exhibited bad caps?

So I got another 1800fp the other day. It just so happens to have a bad logic board also. I was hoping for the PS but I wasn't that lucky. This one won't turn anything on, no leds or screen. The backlight is ok because I can jumper it on and the PS is giving good voltages. Has anyone heard of a solution for this one. I am beginning to think the main IC is fried on this one.
drewcam888 is offline   Reply With Quote
Old 01-30-2010, 10:16 PM   #56
gyeap
New Member
 
Join Date: May 2009
Posts: 6
Default Re: Has the Dell 1800FP exhibited bad caps?

I learn more about the flickering problem. If you use a hair dryer and heat up around the GM5120 chip at the logic board, it could solve the flickering or at least increase the time the backlight turns on. I also bypassed the BLON signal by disconnecting it from the socket and connect it to 5V. This can force the backlight to always turn on.
However, it did not helped because the screen will still turn blank.

So, the problem is that the chip experience a loss (or out-of-sync) of the video signal and decides to blanks the backlight. Raising the temperature can improve the signal stability. It's some kind of timing issue in the video signal path. It might be an inherent design flaw of the chip or board that does not tollerate aging drift of the devices.

Flickering does not happen if the video signal is disconnected.

Can anyone confirm the temperature dependency of this failure?
gyeap is offline   Reply With Quote
Old 08-31-2010, 01:34 AM   #57
gyeap
New Member
 
Join Date: May 2009
Posts: 6
Default Re: Has the Dell 1800FP exhibited bad caps?

I spend a couple of hours more on the Dell 1800FP monitor's logic board with the flickering problem. I found that if I use a hair dryer to heat up the ROM chip (next to the GM5120) above 45 degree C, then the flickering will go away. If it cools down the below this temperature, the random screen on/off will come back. Off time increases with cooler temperature. I have a themometer taped to the chip. I can heat up other parts of the board and let the temperature of this chip rise to this level to cure it. There is no such temperature dependency with the GM5120 and the THine chip.

I probed the ROM signals with an oscilloscope. Unfortunately I could not observe any good vs. bad signals. The fault model seems to be intermittent bad signal timing between GM5120 and the ROM. There were reports that observed changing power supply curing this problem. This is possible as the handshaking signals could be good due to the change in power supply. I notice that there is no decoupling capacitor near the ROM chip, not a good design.
gyeap is offline   Reply With Quote
Old 08-31-2010, 08:12 AM   #58
shovenose
Send Doge Memes
 
shovenose's Avatar
 
Join Date: Aug 2010
City & State: Fairfax, California
My Country: USA
I'm a: Forum Junkie
Posts: 6,127
Default Re: Has the Dell 1800FP exhibited bad caps?

i thought i saw two bulgy caps in the 2nd attached picture...
__________________
1995 Chevy Silverado ~276K.
2010 Ford Escape ~90K.
shovenose is offline   Reply With Quote
Old 09-30-2010, 12:32 PM   #59
rcatank
New Member
 
Join Date: Sep 2010
Posts: 1
Default Re: Has the Dell 1800FP exhibited bad caps?

Severach... HOw did you know that the controller board is fried?

I just replaced the IC chip on my PSU.. but before I had dont that.. I gave 12v and 5v directly to the Controller board with an extra PC PSU that I had laying around that gave a 12v, 5v and ground via Molex connector.


Now I am not sure if the original PSU in the Dell 1800FP is working or not... or is it my Controller board is bad... Still no Green/Orange lights... nothing shows on the screen.. and backlight doesnt turn on either...



Quote:
Originally Posted by severach View Post
The Dell UltraSharp 1800FP has at least 3 flaws including some bad caps.

1) Diode solder connections break
2) Bad caps on display board
3) Bad caps on power supply

On the LG 6870T445D10 power supply the output diode array D906 and D903 solder can break which burns out the ICE2AS01 PWM. Some have mentioned there is a missing zener diode ZD902 that would protect against this but so far no values have been put forth though it seems quite easy to do. Add a half volt to the max value on the data sheet. Measure the working voltage to ensure that we aren't already above the max.

I resoldered power supply D906, D903 and the input cap C905. My ICE2AS01was not damaged. Some recommend removing all existing solder before resoldering.

On logic board L1800FPK 6870T573A62 L1800F containing chips THine THC63LVD823 and Genesis gm5120, the SamYoung SMD caps with the 3 point swirl logo C739 and C207 10uf 16v K3L K3o K3α are bad. On the first logic board which I eventually burned out, they measure 10, 20 ESR ohms out of circuit. On the working eBay replacement they measure 1.6, 3.6 ohms in circuit and 8.5, 8.6 ohms out of circuit so the replacement board wouldn't have lasted long. They are the same type and size as the two 10f 16v C604 and C507 caps found on the infamous 1702FP BN41-00101A AD video board which cause a blank/black screen and flashing leds. Fixing that board is what gave me the idea to check them here on the 1800FP board guessing that they might be from the same bad batch. The logic board SMD caps are all grounded on the negative side so are easy to test and they test fairly well in circuit. Attach one probe to any ground then hit each positive with the other probe. None of the caps test to be in parallel so if any are bad the board has lost some important function and will not display an image.

I replaced video board C739 and C207 with some 10uf 50v non SMD caps commonly found in junk ATX power supplies. C817 had a suspiciously high ESR in circuit but tested fine out of circuit.

Had I not broken the first logic board with too much testing on a bad power supply, replacing C739 and C207 might have repaired it. At first it was able to light the power led yellow/red/orange though no logo ever showed. By the time I learned that the unsafe and unfixed LG power supply required servicing, my testing killed the the logic board completely. The burned out logic board does not light the power led at all.

Eventually I figured out that the 5v caps in the LG power supply were no good. They were not bulged or leaking and had decent ESR at 0.11 ohms. The way I figured it out was to measure the output voltage with and without a top quality capacitor in parallel. Without the extra cap the 5v line measured 4.71v running on the SamYoung 10v 2200uf group, a stretch for 10% tolerance. With my motherboard grade cap the 5v line measured 4.92v. After replacing the three 5v caps the final was 4.96v. The PWM reducing the voltage tells me that the ripple was too high and my good cap cut the ripple down so the PWM could raise the average voltage measured by the DVM.

I replaced power supply C907 and C924 in the PWM section. I replaced C918, C915, and C914 on the 5v rail. I replaced C913 on the 12v rail. Sam Young C911 and C921 on the 12v rail tested fine.

Though I have no proof I suspect that the 1800FP LG power supply is a poor design and the slightest amount of bad ESR in the 5v caps sends the voltage of death into the logic board just like any good Bestec would do to an unwary eMachines board. Fix all power supply problems before testing anything.

I had no problems on the high voltage inverter. This 1800FP is definitely UltraSharp.

Dropping a good cap in parallel with the rest is a fast way to troubleshoot circuits that are partially working. Just as with different ohm resistors in parallel, the cap with the best ESR in a parallel circuit takes the lion's share of the load. If the circuit springs to life you have found the problem.

I fixed a bunch of IWE1100-A access points this way where the 48v POE to 5v converter board wasn't working. The output voltage was about 1.7v and the LEDs were dim or dark. Most worked with an alternate 5v supply in the power port. After about an hour of testing that didn't reveal much other than that nothing was burned out in the voltage converter and it should work. Out of frustration I placed a new cap across the output caps. The green power L.E.D. lit up and the WiFi unit would have been functioning if it hadn't started at a brain dead 1.7v. A few caps later and they were all fixed. There are 5 of the same brand bad caps on the IWE1100, 2 on the POE converter and 3 on the main board. The voltage converter caps see more heat so wear out faster. The mainboard caps should fix problems with unit lockup. The voltage converter caps were hard to get out and even harder to insert so I placed long lead Rubycon 2200uf caps in the cavity where the old caps were and surface mounted the leads. Those units should have a long life now.
rcatank is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2019
Powered by vBulletin ®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 03:50 AM.
Did you find this forum helpful?