Samsung 2043NW Strange Issue with High Resolutions

[canadaboy25]

Hey guys I have a Samsung 2043NW LCD that is showing some strange problems. When I set the monitor to 1600x1200 it works just fine apart from the lower resolution. No flicker at all. When I switch the setting to the recommended 1680x1050 it has a black screen with some strange bars and slowly bleeds to being completely black.

I know that the computer and cable are fine because when I plug another monitor in and set it to 1680x1050 it works beautifully. I looked at the power supply board and none of the caps are bulged but I tried replacing them anyways with no results.  When trying to display the high resolution, a high pitched whine can be heard from the thin board that runs along the entire top of the LCD panel.

This is something I have never seen before. Any ideas on what would cause it to work fine in the resolution lower but not on the recommended resolution?

Thanks

[amyk]

Have you tried a lower refresh rate?

[Rasz]

1600x1200 cant give you picture, because its higher than the native resolution, are you sure you didnt mix those two?
monitor crapping out at max res might be a symptom of old caps = ripple = scaler hangs at max clock rate

2043NW  is a shit TN callcenter grade monitor anyway, why would you want to repair that?

[canadaboy25]

Have you tried a lower refresh rate?

My only two options are 60Hz and 59Hz.  Any way to get more options?

1600x1200 cant give you picture, because its higher than the native resolution, are you sure you didnt mix those two?
monitor crapping out at max res might be a symptom of old caps = ripple = scaler hangs at max clock rate

2043NW  is a shit TN callcenter grade monitor anyway, why would you want to repair that?

1600 x1200 does give me picture it's just blurry and it's auto scaled to the monitor.  That's why there are black bars at the top and bottom of the screen because the picture is too wide to fit the monitor properly.  I replaced all the electrolytic caps on the power supply board and there was no improvement. 

This monitor isn't going to be my main PC monitor.  The quality is plenty good enough for installing an OS onto a machine or for use as a server head.

[Rasz]

aaah analog scaler
try replacing those 3 caps on scaler board
if that doesnt help $5 universal controller http://www.ebay.com/itm/MT6820-B-Universal-LVDS-LCD-Monitor-Driver-Controller-Board-5V-17-42-New/141941269518 just make sure lvds pinout and connectors match

[canadaboy25]

aaah analog scaler
try replacing those 3 caps on scaler board
if that doesnt help $5 universal controller http://www.ebay.com/itm/MT6820-B-Universal-LVDS-LCD-Monitor-Driver-Controller-Board-5V-17-42-New/141941269518 just make sure lvds pinout and connectors match

I tried replacing the three caps and it still has the problem.  The problem now seems to affect 1600x1200 as well.  There were some test points on the thin board that runs along the top of the LCD.  The test points were LP, POL, STH_F, STH_B, STV, CLKV, and OE.  The STV test point is the refresh rate because I get 59 - 60Hz when it is working.  I can set the refresh rate to 75Hz and the test point will change as well.  When I try to display a resolution that isn't working, the refresh rate drops down to 20Hz and will not change.  Also, when the monitor is working the OE pin has a signal and when it isn't working the OE pin is stuck high.  I have posted waveforms for the other pins as well because some of them are different when it isn't working too.

20Hz on one pin and no signal on another doesn't seem right to me.

[Rasz]

I tried replacing the three caps and it still has the problem.  The problem now seems to affect 1600x1200 as well. 

did it go worse after replacing caps?
1680x1050 requires 120MHz, one lvds channel maxes at 112MHz so its definitely dual LVDS = 60x7 = 420MHz per diff pair = rigol wont do it :/ so no point putting scope on lvds signals ....unless they simply disapear when things go bad
I still think its the scaler due to panel giving you good picture at max res before. It might also be flex between the two.

[canadaboy25]

I tried replacing the three caps and it still has the problem.  The problem now seems to affect 1600x1200 as well. 

did it go worse after replacing caps?
1680x1050 requires 120MHz, one lvds channel maxes at 112MHz so its definitely dual LVDS = 60x7 = 420MHz per diff pair = rigol wont do it :/ so no point putting scope on lvds signals ....unless they simply disapear when things go bad
I still think its the scaler due to panel giving you good picture at max res before. It might also be flex between the two.

No it was worse before I changed the caps.  It's been sitting around for a while.  Would a bad cable cause the problem?  I know I have to wiggle or press on the cable to get horizontal bars to disappear sometimes.  Is there anything I can do short of buying a new cable?  Like solder wires between the two boards?  There aren't very many pins.

[Rasz]

you can buss all the pins with a multimeter in diode mode

wait, how was it worse before changing caps when you have picture of it somewhat working before and say it does nothing now ?

I would also reflow that scaler IC for good measure (with flux + hotair gun)

[amyk]

http://www.beyondinfinite.com/lcd/Library/Chungwa/CLAA170EA03.pdf has some typical waveforms for those signals, but I think the panel is not the problem.

I would check the main board voltages for ripple and bad solder joints. Try applying slight pressure to parts of it while it's operating.

[canadaboy25]

you can buss all the pins with a multimeter in diode mode

wait, how was it worse before changing caps when you have picture of it somewhat working before and say it does nothing now ?

I would also reflow that scaler IC for good measure (with flux + hotair gun)

Ahh ok that's a good idea.  I'll try that.

Sorry, I worded that poorly.  I plugged the monitor in to try it before I changed the caps because it was sitting around for a while.  When I tried it the problem happened with the 1600x1200 resolution as well.  Any resolution below that still works fine.  I don't know why 1600x1200 stopped working now.  Maybe it's due to me plugging and unplugging the LCD cable again or it might be the fact that I was trying it with a different PC.  Either way, replacing the caps had no effect on the display at all.

The scaler IC is the one on the board with the VGA connector, right?

[Rasz]

yes, its the one with TSUMU58 under the sticker
btw those chips are $5 on alliexpress if you are desperate