Emachines LCD LE1938 2 seconds to black

[dredger]

Hello all,

I have browsed your forums and seen many posts regarding the "2 seconds to black issue". Mine is quite similar in most aspects and I have a semblance of my "next step". Just wanted to verify with a knowledgeable community before proceeding.

First off, I am not an electrician. I am a satellite technician so I have some limited knowledge of components and circuitry but i deal way more in frequency theory than component level issues. That said I can "fake it till I make it" and get this fixed, I just know it.

My issue is with a Emachines LCD LE1938 monitor. I took it apart to place it in a suitcase for a small project of mine. It worked fine before I moved it, that is key; it is entirely due to my error that it broke.

So I power it on with a input signal from my PS3 using an hdmi to dvi connector. I get what appears to be full power on my 4 back lights (no noticeable dimness) and I see the "eMachines logo" for about a second, after which the screen goes black. A second or so later the screen comes back on and shows the PS3 Home screen for about 2 seconds. At this point the monitor actually shuts down and the amber standby light comes on the power switch. I have tried shining the flashlight into the screen to see if an image is still present and there isn't one.

Steps I have take so far:
I have replaced 4 capacitors on the board.
470 microfarad/35V
220 microfarad/35V
1000 microfarad/35V
1000 microfarad/50v

The last one was originally a 680 Microfarad/35V but I couldn't find a replacement locally and tried this.

The four replaced caps weren't noticeably bad, however if you closed your eye and jumped on one foot they did seem to possibly have a very very very slight curvature to their tops, nothing like some bad caps i have seen.

Next step:
I have ordered proper rated capacitors for the entire board. I plan on replacing them all in a few days. However, I am not convinced this will fix the problem. Just losing hope that it is something simple I guess

My other thought is that I have a bad CCFL tube. I was reading some other threads saying that a bad tube "could" cause the protection circuit to engage. Like I said earlier I notice no difference in brightness and did not see color distortion, such as red hue, like others mentioned as signs of a bad or aging CCFL but my monitor isn't staying powered with back lights off like others so I am thinking it is a protection circuit engaging.

Does anyone have any other ideas or opinions on this. BTW I know I shouldn't have changed the farad rating with a higher one, but I was antsy to see if it worked, it will all be replaced with proper rated caps in a few days.

PS When I get back from work I will see about compressing the photos I took and adding them to the post. Problem being they are 6MB a piece, so can't attach them at the moment.

[PlainBill]

Re: Emachines LCD LE1938 2 seconds to black

There are two possibilities - you caused the problem, or the failure was a coincidence. If you caused a failure, the most likely event was a broken CCFL. If your suitcase went as checked baggage, that is very possible.

Replacing the caps is a good idea. If you haven't ordered caps yet, also order a .01uF 1KV ceramic cap. Use that as a substitute for a suspect CCFL.

PlainBill

[dredger]

Re: Emachines LCD LE1938 2 seconds to black

Hi again,

So I started working again when I got home. I had the idea to try turning all the lights off and turning on the monitor. I saw a red hue to the screen. I watched this for three restarts and was convinced that meant I had a CCFL issue from reading other posts listing red hue as a symptom of a broken CCFL.

I tore the screen the rest of the way apart and removed the back lights. I powered up the boards without the 30 pin cable so the monitor itself wouldnt have any power and watched the backlights. All four lights lit up in what appeared equivalent brightness (read: blinding).

So now I am stumped again, the issue persists, the backlights seem fine; no noticeable difference and no noise. I guess I will just follow up with the capacitors when they arrive. I don't think I will try new bulbs due to their price being equivalent to buying a used LCD.

Lastly Bill,

To use a ceramic capacitor as a bypass for problematic CCFL would I need to desolder then connector on the inverter board and solder the capacitor at the end of the circuit? If not could you provide more details on how to incorporate the capacitor?

Thanks!

[PlainBill]

Re: Emachines LCD LE1938 2 seconds to black

Hi again,

So I started working again when I got home. I had the idea to try turning all the lights off and turning on the monitor. I saw a red hue to the screen. I watched this for three restarts and was convinced that meant I had a CCFL issue from reading other posts listing red hue as a symptom of a broken CCFL.

I tore the screen the rest of the way apart and removed the back lights. I powered up the boards without the 30 pin cable so the monitor itself wouldnt have any power and watched the backlights. All four lights lit up in what appeared equivalent brightness (read: blinding).

So now I am stumped again, the issue persists, the backlights seem fine; no noticeable difference and no noise. I guess I will just follow up with the capacitors when they arrive. I don't think I will try new bulbs due to their price being equivalent to buying a used LCD.

Lastly Bill,

To use a ceramic capacitor as a bypass for problematic CCFL would I need to desolder then connector on the inverter board and solder the capacitor at the end of the circuit? If not could you provide more details on how to incorporate the capacitor?

Thanks!

Since the CCFLs work, this is a moot point. Instead, turn your attention to the cable from the signal board to the LCD panel.

For others who want to try it, I haven't tried this yet, but the easiest way to do this would be to solder the cap to the CCFL connector pins on the bottom side of the board. If it works, cover the solder joints with hot melt glue.

PlainBill