NEC monitor help!

[ante1]

Hi All,

I could use some help with my NEC Multisync LCD 1920 NX. The problem is the backlight doesn’t work and I haven’t a clue; a service manual and/or some good advice will be greatly appreciated!

[move]Please![/move]

PS. You guys are the only thing between this monitor and a dumpster! ;D

 

[SM2GXN]

Hi Ante!

Have repaired couple of laptops with same fault, no back light.
In both (two different brands I can't recall which) there was a cold solder joint right at the legs of the transformer. A good magnifier is a must and I tell you there is lot's of electronics in there to fire up the back light

 

[ante1]

Hi Bjorn,

Thanks for your suggestion; I have had a close look now at the intestines of the monitor. And yes there are quite a few parts for the backlight! To start from the beginning: If I look at the display in a certain angle I can see the picture, the menu settings seems to work fine but no backlight. The label at the power input socket says 12Volt 5A but it draws just 0.6 and this might be correct since the backlight usually is the main power consumer as far as I know. At a first glance there are no burns or popped parts but there are a lot of very small parts  ….  (where did I put my magnifying glass?)…. so I’m not 100% sure yet. I hate SMD:s, especially the smallest once like these.   The white connector (8 wires) to the left of the main board (see picture) is for the driver board. The red wire carry’s 12V supply to the driver PCB but all four outputs on the driver PCB are at 0VAC. So what I like to know is, are there any signals (brightness, blanking or other) missing from the main PCB which suppose to switch on the driver PCB or is the problem on the driver PCB itself? I guess without very good knowledge or a circuit diagram it’s very hard to isolate the problem. Any thoughts anybody?

 

[ante1]

There was supposed to be pictures in my last post!!  >  > I got a message “UPLOADER IS FULL” when trying to attach the pictures; they weren’t anywhere near the maximum allowed size so I don’t know what’s wrong here????? ???

 

[ante1]

Thanks Mike, you’re the best! ;D

Mike just fixed the problem as always! Here are the pictures:

View attachment 37186

View attachment 37187

 

[ante1]

Hi again,

I got some schematics from (http://ib.forum77.com/index.php?mforum=technical&amp, thanks sawwa7! Lots of “black boxes” but maybe someone has seen anything similar. However there are no backlight circuit  (if I did not miss it) but I think the 8way connector on sheet 2 (left side) might be the one going to the backlight circuit. Any ideas on this guys? Thanks!

PS. The distance between the monitor and the dumpster is decreasing! ;D


[attachment deleted by admin]

 

[ante1]

And decreasing!

 

[SM2GXN]

Hi Ante!

Sorry for not being able to help you but have you tried to measure across the CCF tubes?
I pass a link on how to measure the voltage present in the CCFT circuit, not much but anyway it's a good start.
Hopefully this will shed some light on your problem.

Bjorn

 

[SM2GXN]

OOOPS!!

Forgot to send the link, here it is  ;D

http://www.pacificdisplay.com/ics_app%20notes/ccfl-elp/ccfl_apnote.pdf

 

[harrassed]

Had problem with batch of 1560 monitors - Fault power on via side switch ,backlight comes on for split second . could revive by switch off(side switch) and power on holding reset and input . Fault was batch problem with invertors

 

[ante1]

Thanks Bjorn,

I have to study this for a while and see if the old brain puts out something useful! Any other suggestions are as always welcome!

Thanks again!

 

[a1racy]

That model has a know defect with the transformer shorting out on the inverter (what you all call the backlight bourd/circuit). There is an upgraded board for it available at Mitsubishi--who has the repair contract for NEC.

 

[ante1]

Oh yeah, I forgot to update this one! Sorry!

I found that the inverter transformers (both of them) had open circuit (secondary)! I scavenged a couple of working inverters in a dumpster at work and the thing is now working perfectly. I can’t figure out why both transformers “died” but as things developed, who cares? ;D

 

 

[srich70546]

Have you checked the 12v supply to the backlight inverter or the inverter.  These seem to be the most common backlighting problems.

 

[ante1]

The 12V supply was fine, only the output from the inverters was missing.