1800FP Green light on but no image on screen

[Welchs101]

Hi,

A friend brought over a 1800FP monitor he got from the flee market. When you put power to the monitor the green light comes on but there is no image on the screen. If i shine a flashlight on the screen there is not even a faint image on the screen.

I have an 1800FP monitor that i use on my computer but i took it apart to help my friend fix his monitor. So i have a working 1800FP for comparison.

What i did was the following:
To help identify what was causing the problem i disconnected the inverter board and had only the power supply board and the logic board connected. I measured the voltage differences at the connectors. I actually found a difference.

Looking at the enclosed pic you will find two letter "A". One at the connector between the logic board and the inverter board. One at the "+" side of a capacitor. I was measuring the voltages at all the caps and comparing those measurements at the same locations on the "good" monitor. I found that the points labeled with the "A" are at the same "node".

On the good monitor the voltage is a constant ~ 0.034V. WHile on the "bad" monitor the voltage is constant 3.1V.

Any ideas? I think the logic board is "bad" but what i dont know is if the bad component is something i can replace or not. Any ideas how to narrow it down.

I know i could put the good logic board on what i suspect to be the bad logic board but i dont want to do this just yet because i dont wnat to "kill" my monitor as well.

Any thoughts?

[Welchs101]

Re: 1800FP Green light on but no image on screen

i placed one of the A's on the wrong cap. I have corrected the figure and you can used the enclosed pic. The "A" on the cap is placed correctly now.

[dobber]

Re: 1800FP Green light on but no image on screen

try changing that serfice mounted cap out with a standard cap. I just did it with 3 of them on a Dell 1702fp. Is it about a 16 volt 10 UF, that is what 2 of my bad ones were.

[alexanna]

Re: 1800FP Green light on but no image on screen

My only sugestion would to verify that all the voltage regulators are working correctly with the correct out put voltages.

[Welchs101]

Re: 1800FP Green light on but no image on screen

I addeda a 10uf/50V radial cap to the logic board. I did NOT remove the old one i just soldered the new 10uF cap in parallel to the suspect one.

I turned on the monitor and nothing happens no image displayed on screen.

WHen i connect ALL the connectors i read the following: Voltage at that node varies from ~ 3.1V to ~ 5V. Recall on the "good" monitor it did not vary at all and the value was ~ 0.034V.

[PlainBill]

Re: 1800FP Green light on but no image on screen

I addeda a 10uf/50V radial cap to the logic board. I did NOT remove the old one i just soldered the new 10uF cap in parallel to the suspect one.

I turned on the monitor and nothing happens no image displayed on screen.

WHen i connect ALL the connectors i read the following: Voltage at that node varies from ~ 3.1V to ~ 5V. Recall on the "good" monitor it did not vary at all and the value was ~ 0.034V.

Is that node identified at the inverter?

PlainBill

[Welchs101]

Re: 1800FP Green light on but no image on screen

hi Bill,

Not sure what you mean. This node does go to the connector as i showed inthe picture. Is this what you mean?

[PlainBill]

Re: 1800FP Green light on but no image on screen

hi Bill,

Not sure what you mean. This node does go to the connector as i showed inthe picture. Is this what you mean?

We have to think system. What is connected to that connector? Yes, I know, a cable. Presumably it goes to the inverter. Is there any information on the inverter that would give us a clue as to what the signal is?

PlainBill

[Welchs101]

Re: 1800FP Green light on but no image on screen

bill,

i looked on front and back of both the logic and inverter boards (see enclosed pics).

Just wanted to recap what i have done.

Recall, that i have a "good" and "bad" monitor. I disconnected the inverter board from "both" the good and bad monitor. Why: Because if the inverter is indeed whats causing the bad monitor to be bad then if i disconnect it then i should see similar voltages on both boards at various sites on the logic board (well this was my assumption anyway..........is it a good one?).

What i found was that the voltages between the good and bad matched up fairly well except at two points.......granted i did not look at every possible voltage node.......but i did look at all the caps and few of the regulators. The two points where the voltage did not match up are pin7 of the connector between the logic board/inverter board and the "+" side of the cap (10uF/16V......in the pic u will see i soldered a known good cap in parallel....this cap was added after my voltage measurements were made). What i found was pin7 and this "+" side of cap were at the same node. On the good monitor the voltage reading was ~ 0.034V and on the bad monitor its ~ 3.1V.

SO based on this i made the assumption that the inverter board was not the problem but the problem was somewhere on the logic board........is this a good assumption?

Does this help? Or confuse the issue? let me know and i can make more measurements and put results in a table if you like.

[Welchs101]

Re: 1800FP Green light on but no image on screen

i decided to post the measurements i made. I hope they reveal something to someone.

Note: I made measurements on the good and bad board.
Note: I made 3 sets of measurments on the good board.
Note: I made 3 sets of measurments on the bad board.
Note: one set of measurements were with the inverter diconnected (NoInverter) and the controller board not connected (NoController). I am calling the controller board the one with the on/off switch on the bront of the monitor.
Note: One set of measurements with controller connected (YesController) and inverter not connected (NoINverter)
Note: One set of measuremetns with inverter connected and controller connected (YesInverter and YesController)

See enclosed files. All measurements are in volts.

Note: I placed black lead on one of the "screws" in the board and the red lead from the multimeter on the "+" of the caps.........or the red lead on specified pins in the figure.

If you have any questions please let me know.

[Welchs101]

Re: 1800FP Green light on but no image on screen

Anyone have any thoughts?

I was thinking that based on the results that its the logic board that has the problem..........just not sure where............anyone have any thoughts?

[alexanna]

Re: 1800FP Green light on but no image on screen

Could you provide a photo of all the boards somewhat together straight down with no flash, we really need to get some idea what all the connectors are.
The connector you have labeled a, b, c, d ECT. What does it connect to?
Use your test inverter or another monitor to turn at least on back light in the bad monitor to make sure no image is visible; some can be very difficult to see.
On some monitors they identify what some of the pins are on the connector from the logic board to the inverter/power supply. An example would be
#1 5volts
#2 5 volts
#3 ground
#4 ground
# 5 backlight on
#6 Dim
#7 12 volts.
These are just examples I made up, and I realize your boards do not identify the voltages.
On the working monitor it may be helpful to know what these voltages are, you are going to have to take two readings one with the monitor off and another as you power the monitor on.
It also might be a good idea to adjust the brightness up and down to try to identify the dim pin on the connector. You could identify the backlight on signal by watching the voltage change on one of the pins as the monitor goes into a sleep mode. This may give an idea to what's happening.

[Welchs101]

Re: 1800FP Green light on but no image on screen

Hi,

The measurements i posted already are with the monitor powered on and off.

For powered off => NOcontroller.....ie....controller from front of monitor not connected......this means the monitor is powered off

For powered on => Yescontroller

For inverter board connected => YesInverter

For inverter board not connected => NoInverter


I am also enclosing a pic of the logic board

is this all the info you need?

[steve2]

Re: 1800FP Green light on but no image on screen

Heres the service manual with everything you need. https://cdn.badcaps-static.com/pdfs/...ee6fb5150e.pdf

[alexanna]

Re: 1800FP Green light on but no image on screen

Sorry my mistake the connector I asked about a, b, c, d is the connector you labeled L through S. So that is to the inverter.


wow the service manual should help

[steve2]

Re: 1800FP Green light on but no image on screen

Looking at your (S) test point should be your 5 vdc on pin 8 of J702 (page 33, connectors , far right on manual). Since you have the 5 vdc with the inverter plug off, then I would start at the inverter board.

[steve2]

Re: 1800FP Green light on but no image on screen

Are the readings on the powerboard output correct? Last page of the manual, far right. With evrything hooked up, do you have a 5vdc signal. I know you had iton pin 8 of j702 with the inverter board disconnected. The power supply board 5vdc supply may be too weak to power the inverter. IC901 is a common failure on this monitor ($6 part).

[Welchs101]

Re: 1800FP Green light on but no image on screen

steve,

i measured the voltages coming out of the power supply board.....for the 5V pins i measured 5.11v and 5.11V.

Regarding your comment about 5V on pin 8 of J702..........i am still trying to digest the manual and find where you say it should be 5V. I sure you're correct......just dont see it yet.

If its the inverter board..........what do you think it might be. I have looked at the schematic but not sure i can find the inverter board.

thanks.

[Welchs101]

Re: 1800FP Green light on but no image on screen

steve,

i remeasured the 5V pins on the power supply connector. the measurements i previously gave you were with the power supply disconnected from the logic board.

with the power supply board connected to logic board and logic board connected to inverter board the 5V pins on the power supply board measured between 4.98 and 5.04V.

[Welchs101]

Re: 1800FP Green light on but no image on screen

i have a few updates this morning.

I swapped parts between the good-working 1800FP and the non-working 1800FP.

1) I put the power supply board from the non-working monitor into the working monitor. The logic board and the inverter board were not replaced. And the monitor came on!

2) I put the inverter board from the non-working monitor into the working monitor. The power supply and logic board were not replaced.........and the monitor came on!


So based on these results i would say the problem is on the logic board.

Now the question is ........is this something i can fix or not.

Any thoughts on how to proceed?