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...

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...

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...

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.

Re: Has the Dell 1800FP exhibited bad caps?

eguevarae,

I guess you meant pin 8 of the signal that goes from the logic board to the inverter. The signal will go hi/lo with the backlight on/off. I had figured out that this was the signal that turns on/off the backlight.

When the VGA cable is unconnected, the signal and backlight will stay on. So, the fault should be in the logic board. The pin 8 signal traced to pin 40 of the GENESIS gm5120 chip (pin name GPI0). So, I think the chip is sending the random backlight on/off signal.

I don't...

Re: Has the Dell 1800FP exhibited bad caps?

I am rapairing a DELL 1800FP display. The problem is that when VGA signal is connected, the backlight randomly turns on/off about half to several seconds apart.

The logic boad has two caps with high ESR: C739 and C207 as noted by severach. I added parallel capacitors to fix them. However the probelm still persist. C739 measure good 5.0V.

All caps in the power supply board measure good ESR.

The backlight will turn on persistently if the VGA cable is unplugged. This showed that the inverter board...