SyncMaster 740N strange lines

[gypsy]

The backlight had no problems staying on, but I opened it up to look just in case. The PSU looks like this (image reused from another 740N thread):



Same caps were blown, the infamous CapXons. 25V 820uF, replaced with Nichicon equivalents. The problem, both before and after the replacement, is THIS.

Every time I power it up, the lines are different/begin in different positions, and are initially bright, then start fading to grey. Also, as you can see (compare the image with the reference on my netbook towards the end), vertical lines are fine and drawn to proportion, the issue seems to be only on horizontal lines (which exhibit the problem and are also out of proportion, the image is beyond stretched). I looked on the controller board and everything *looks* fine (a few chips, a lot of small resistors, and 3-4 small-value caps that look fine). Anyone know where the problem could lie?

[retiredcaps]

Re: SyncMaster 740N strange lines

The PSU looks like this (image reused from another 740N thread):

In the future, please use the manage attachments to insert pictures to threads (but NOT inline).

Also, we prefer pictures of your particular board. Reusing other peoples pictures is only a last resort (i.e. you have no camera). Reusing someone else's picture, in the context of troubleshooting, is liking asking a surgeon to operate on you using their xrays.

I looked on the controller board and everything *looks* fine (a few chips, a lot of small resistors, and 3-4 small-value caps that look fine). Anyone know where the problem could lie?

Get a magnifying glass and check the solder joints on the input port (VGA and/or DVI). If there are no obvious poor joints, reflow them anyways.

Also check your ribbon cable connections. Clean them and reseat them.

[gypsy]

Re: SyncMaster 740N strange lines

I reflowed both the VGA and panel connector (pictures taken before this was done) - no improvement. Note that this problem occurs even without a VGA signal, the OSD/no-signal screen exhibits the same issue.

Apologies for the inline posting. I've taken pictures of all boards, front and back, and attached them properly this time.

3,4,5 are the actual LCD driver board (attached to the top of the LCD).
6,9,10 are the power board.
7,8 are the LCD logic board.

[Toasty]

Re: SyncMaster 740N strange lines

Looks like a bad panel or TCON. Hope PlainBill or Wizard catch this.

Toast

[jetadm123]

Re: SyncMaster 740N strange lines

You can also try checking the voltage regulators on the logic card. Bad regulator(s) can cause video problems. There are two on the left side of the board marked APL1117. One has a 3.3V output and I'm not sure what the other is. Measure and report voltages. Also, there seems to be a missing chip in the upper left corner. Did you remove it?

[gypsy]

Re: SyncMaster 740N strange lines

The bigger one has 5V in and 1.8V out. The smaller one (right on the edge) has 5V in and 3.3V out. I did not remove anything from the board.

[jetadm123]

Re: SyncMaster 740N strange lines

The bigger one has 5V in and 1.8V out. The smaller one (right on the edge) has 5V in and 3.3V out. I did not remove anything from the board.

These voltages look to be correct. Just wondering if there's some method to perform a factory reset? Usually, it's holding down a sequence of buttons while powering up the monitor.

[cynz]

Re: SyncMaster 740N strange lines

I reflowed both the VGA and panel connector (pictures taken before this was done) - no improvement. Note that this problem occurs even without a VGA signal, the OSD/no-signal screen exhibits the same issue.

Apologies for the inline posting. I've taken pictures of all boards, front and back, and attached them properly this time.

Check out the panel serial no. if it looks like AUxxxxxxx, or LG Samsung made. Mostly, the signal controller chip on the panel has burnt inside. I had the same experience before, by replacing another compatible panel, then it back to normal.