LG Monitor Broken; Vertical Colored Lines

[kyranc]

Hi, I've had this LG l204wtx for a while now. Several months back, whenever I'd turn it on, it would take a while to power up. Every day the delay got longer and longer until it stopped turning on altogether. Pretty characteristic of dead power supply caps.

So I got some new caps and replaced them and now have the monitor turning on fine with no delay. But the issue is, every other vertical pixel column isn't showing. Instead it will be various colors, from plain black to blue, red, yellow, green, etc. This manifests itself as a color tint when viewed from afar, as well as an aliasing effect from every other column of pixels being missing. When it first starts up, the color of the vertical pinstripes will flicker back and forth. The longer it's been on, the more stable the color. The fact that it tends to settle down on a color after warming up for a while seems to hint at another capacitor problem perhaps? (I'm pretty ignorant in this field of hardware so my diagnostic skills amount to mere speculation)

I've already replaced all the caps on the main board connected to the PSU apart from the jumbo ones, which appear to be fine. The smaller ones (most around 1000uF 25V) were visibly swollen before I replaced them so I thought that would have done the trick. There's a couple smaller caps on the second board with the video connectors. I've been debating replacing them but they look fine and are in tight quarters so I don't want to risk damaging anything unless there's a good chance it'd fix the problem.

The pinstripes go through the monitor's menu as well, which makes me think it'd be isolated to the power board and not something to do with the video connectors. Another option I considered was maybe bad ribbon cables? There are two pairs of ribbon cables going from the power board to the video board, a larger one and accompanying smaller one with only a few pins. There's also the ribbon going from the power board to the display itself. I've tried reseating all the ribbons several times to no avail. I'm not sure how data is distributed through the ribbons but could this vertical striping thing indicate maybe one of the ribbons is damaged? I've tried squeezing the case around the edges to see if I can isolate any mechanical failure points but I've had no luck so far.

I'm hoping there's a display guru out there who has an idea what's wrong from the symptoms and can give me some guidance.

Thanks a bunch!

 

[kyranc]

Thanks for the tip. I replaced them with a few caps I bought as well as some that I recycled. I only specified uF and voltage and they gave me some Philips ones. Wasn't aware of the ESR factor. I figured anything was better than the cheap caps that were already in there.

Do you think the ripple could be causing every other column of pixels to not display properly? The backlight is strong and steady and the monitor turns on with no issues so I assumed the caps were doing their job. I suppose it could be messing up something more sensitive down the line.

Perhaps I should buy a capacitor kit off ebay? Is there some measurement that it should be under or do I just specify low ESR?

 

[kyranc]

I think I threw out the larger ones since they were the first I replaced. But the 3 smaller ones I replaced a bit later on are still on my desk. They say Samxon KM(M) U6A, V5A, and V9B. It is possible the Philips ones I put in happened to be low ESR. Like I said, I only specified uF and V.

Is there any chance that replacing the 2 caps on the other board (the video board?) would help? Replacing the caps on the power board is what brought the monitor back to life but maybe their failure caused some problem with the caps on the other board? I can't tell if that sounds farfetched or not. I guess I could just replace them to be sure but it's a bit of a pain in the ass to rip the monitor apart and my soldering iron is kinda bulky so I'm kinda sketched out about the proximity to other components.

Maybe tomorrow I'll try to replace the last two caps and write down the model of the Philips replacement caps I put in to check if they're low ESR.

Also another thing I remembered, when I disassembled the monitor the first time, I peeled off some metallic tape off the metal cover that was attached to the main board chassis. At the time I just thought it was holding the chassis in place since it's not actually screwed into the rest of the monitor, but is it possible I cut a ground connection or something?

 

[kyranc]

Yeah I'm not surprised they're cheap. I guess it's possible the other ones I threw out were low ESR but they looked the same as the ones I listed above but just bigger of course.

I'm going away for the day I think but if I get time in the morning or tomorrow, I'll try to take some pictures. I'm also gonna have a look at that grounding situation and recheck all my solder points. I'll probably see if I can put those smaller ones in delicately on the off chance that that solves it.