Dell SE198WFPf - Backlights go off after 2 seconds

[alexanna]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Ok, I've now had 2 different Dell SE198WFP monitors with the same problem and I had to read numerous posts on numerous blogs looking for a solution before I actually figured it out, everything that I'd read suggested bad capacitors on the inverter board (and I'm sure that's an issue, but it wasn't mine). After replacing all of the caps on the inverter I still had the same problem.

Long story short, I found (on both of my SE198WFP monitor's) that at least one of the four CCFL backlight tubes had a burnt wire on the end of it. Period.

Now I'm not sure if this is a common problem with this monitor, but it was in fact the problem with both of mine, and after fixing these wires both monitors now work just fine :-) It seems that all four CCFL's have to pull the same amount of current or the monitor trips the overload and shuts down the inverter. I hope this helps!! And good hunting :-)

You hit the nail on the head; one CCFL fault will shut down the backlights.
I see quite a few monitors with CCFL wiring problems; it's usually where the small return wire solders to the CCFL.
If you have A 2 second to black problem that's corrected when a known good CCFL is substituted, inspect the wiring very closely where it goes through the silicone end cap. If any discoloration of the wire is noticed there is a good chance you found the problem.

[cynz]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Did you also try this with the monitors inverter, or better yet by hooking them to the inverter in another monitor? It appears that the voltage is not high enough to fully light them. I saw this when I was using an inverter with a much lower output voltage. If you got the same results, I would say the CCFLs are bad, the do have a pinkish tint.

In the USA, CCFL Warehouse has the reputation for being a reliable source.

PlainBill

Hi PlainBill, thanks. You are right. The ccfls are still ok to work after testing by hooking them to another inverter, which can fully light them up. It appears that the old one cannot produce the voltage high enough. So do I need to upgrade the capacitor values? Like replacing 3 black 470uF ones to 820uF ? As it is the closest value that I have. Any suggestion, thanks.

[PlainBill]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Hi PlainBill, thanks. You are right. The ccfls are still ok to work after testing by hooking them to another inverter, which can fully light them up. It appears that the old one cannot produce the voltage high enough. So do I need to upgrade the capacitor values? Like replacing 3 black 470uF ones to 820uF ? As it is the closest value that I have. Any suggestion, thanks.

Not a good idea. The original design was sound, the problem is something has deteriorated. If the caps appear to be bulged, show other signs of failure, or are of a known bad brand (for example, replace Elite caps on sight), replace all. These show no signs of bulging. What is the voltage of the inverter supply? One point to measure it is across C21. From the top side of the board J15 is a good point.

PlainBill

[rz1138]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

You have a PM

Any chance of publishing the steps to open the case. I'm worried I'll cause more damage than necessary guessing.

Excellent thread-- I've got the same exact problem of screen going to black after a couple of seconds.

[budm]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

See pictures here:
http://s807.photobucket.com/albums/y...ell%20E198FPF/

[rz1138]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Thanks. That helped--I hadn't thought of prying bezel from inside. A credit card sized mini scraper made it a breeze with no scratches or broken tabs. I slid the beveled edge between the screen and bezel and lifted straight up, working my way around the screen to the button corner.

I got the backlight apart and found that a negative lead was indeed separated from one of the ccfl tubes. If that doesn't fix it, I'll check each ccfl with the resistor method.

[budm]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Can you clarify the "I'll check each ccfl with the resistor method." ? Thanks.
by the way, burnt out this bad?

[rz1138]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Can you clarify the "I'll check each ccfl with the resistor method." ? Thanks.
by the way, burnt out this bad?

I got idea from romansroad post but wasn't able to find the thread he mentioned.

You can substitute a resistor for a backlight (search under this to see that thread). I would then sequentially go through the turn on steps with the resistor placed at each separate HV point. If the other ccfls stay on, then the one you faked out the PS board with the resistor is the bad ccfl.

No, not burnt at all. It just looked like it was a weak solder point that broke apart. I soldered it back and now it's working again.

This wasn't my monitor originally so I don't know if it was dropped or how else the wire could have separated so cleanly--especially packed so snugly in that end cap.

[rz1138]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

No, not burnt at all. It just looked like it was a weak solder point that broke apart.

Here's a picture.



I had to slice the end cap in half to get it off. I was able to resolder the wire and get the silicone cap back on. Once I replaced the yellow tape that was around it and put the assembly back in the screen frame it was fairly secure.

[CommTechRepair]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

This thread came up for my search on a datasheet for a OZ9937GN. A 9937 is not the same as a OZ9938. I couldn't find a datasheet, but the brochure I've attached includes application notes with the pin-outs.

[Jazzmarazz]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Since I am not the only one necro-posting, I might as well share my own problem.
I was excited to add this monitor to my collection because both of the other monitors on my desk were ones that I had fixed for $25 total and I purchased this one cheaply too.

The problem as you may have concluded is that I have 2-seconds to black. With a bright light, I can see that any signal I send to the monitor is still on the LCD, but the CCFL bulbs go out. The strange part is that if I leave the monitor unplugged for half an hour, I can get up to a whole minute of flawless use until the lights eventually go out. At this point, the power LED remains lit and I can turn on the display which goes to black each 2-seconds.

Unfortunately when I opened this monitor, I found nothing wrong with the power board. There were no bad capacitors, no cuts, shorts or even dust as far as I could see! Last week I stepped on my multimeter and RadioShack will be closed by the time I can get there tonight, but I have opened the LCD to look at the bulbs. They did not look odd so I put it back together.

I did just read that the bulbs can potentially have a loose or cold soldered joint, so I may check that within the next hour. I pride myself on having very nimble fingers, but opening an LCD is incredibly difficult. Wish me luck!

[Jazzmarazz]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Since I am not the only one necro-posting, I might as well share my own problem.
I was excited to add this monitor to my collection because both of the other monitors on my desk were ones that I had fixed for $25 total and I purchased this one cheaply too.

The problem as you may have concluded is that I have 2-seconds to black. With a bright light, I can see that any signal I send to the monitor is still on the LCD, but the CCFL bulbs go out. The strange part is that if I leave the monitor unplugged for half an hour, I can get up to a whole minute of flawless use until the lights eventually go out. At this point, the power LED remains lit and I can turn on the display which goes to black each 2-seconds.

Unfortunately when I opened this monitor, I found nothing wrong with the power board. There were no bad capacitors, no cuts, shorts or even dust as far as I could see! Last week I stepped on my multimeter and RadioShack will be closed by the time I can get there tonight, but I have opened the LCD to look at the bulbs. They did not look odd so I put it back together.

I did just read that the bulbs can potentially have a loose or cold soldered joint, so I may check that within the next hour. I pride myself on having very nimble fingers, but opening an LCD is incredibly difficult. Wish me luck!

Turns out I had one loose cable on a CCFL. I cut the rubber nub at that particular end in half and added a tiny bit of wire to extend it so that the bulb was reachable, adding heat shrink tubing of course. The tubing helped keep the bulb tightly fitted back in place.

Although no one responded. the thread helped me out because the monitor works as it should now! Three-monitor Eyefinity successfully setup.

[budm]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

The suggestion was given on post46, 48.

[arjaysmithjr]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

I was in the same boat as everyone else here, so I looked at the caps first,
they looked fine, then I went for the CCFLs. Actually they looked OK too, but
since I went that far, I figured I'd resolder them. Plugged them back in, and
no more 2 second blackout!
BUT
Does anyone know where I can get an exploded view of an Innolux MT190AW01 v.5?
Yes I should have taken photos as I disassembled the thing, but I got carried away.
Thanks

[arjaysmithjr]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Sorry, never mind. I said a little prayer and it went back together fine.
I'm using the monitor now. If the CCFL's go bad, or the solder joints,
again I think I'll try changing over to LEDs.
Thanks again for this thread. It saved this monitor from the dumpster.

[jasonwang]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

I have this monitor and seem to your monitor, but it's difference. My CFFL is ok. When black light on to off. I test oz9937:
4 pin: 1.5V
9 pin: 1.2V
10 pin: 0.8V
14 pin: 3.0V
I have no idea for this. who can tell me ? how to repair it?