Samsung LCD - Weird Failure - Trying to Repair

[katzohki]

I have a weird failure with this Samsung 215TW. Let me start off by stating what I've done:
I replaced the bad caps (bloated CapXon) on the power supply board and checked voltages at the local regulators. Everything looks good with voltage, but no fix yet. I also checked over the main board for bad solder joints and other physical maladies.
Here's a picture of the strange glitch:

As you can see, it looks pretty scrambled. This should be something like a message stating "no source found" or something like that. It floats around the screen. And when I try to change inputs, it pops up into the upper-left corner where the input message box would normally be. Besides that, I haven't got video when testing the inputs. To be fair, and you can beat me up over this if you want, I have only tested the VGA input. But I really don't think that's going to be the issue because something looks wrong besides input. I'm thinking it's a communications issue somewhere on the main board. There is a service manual available online that details the schematics of the monitor.

Any ideas?

[AndyC_772]

Looks like there's some dual port RAM that's not getting written.

[katzohki]

Hm, there's a 128M SDRAM chip, but it looks like the only thing writing to it is the main ADC / Prescaler / LVDS. I'll see if I can give it a probe.

[fluxcapacitor]

It looks like the eeprom is corrupt to me .

[tautech]

In VGA source mode are you supplying a PC video signal?
Maybe your card won't recognize it?

What was the original fault?

[katzohki]

Yeah, I'm afraid it might be a corrupt EEPROM or firmware.

To answer tautech's questions:
Yes, supplied VGA from PC
It does this even unplugged, so don't think source is the issue.

Original fault was this, I inherited it. It's really a nice monitor that I'd love to fix, but eh if it's beyond economical repair I've only spent a few bucks on caps so far.

[onlooker]

I think the easist fix is to get a universal lcd tv logic board. On ebay an hdmi one with remote ctrl is about $12 (search for hdmi universal lcd board). The VGA only ones are about $6 each. The rest will be mostly mechanically fiting it to you monitor and rerouting the power supply.

[urbis]

On Samsung TVs, when the caps fail, it's notorious for corrupting the EEPROM.

There may be a reset by shorting a couple of pins, but not entirely sure.

[Dave Turner]

Jackson Pollock eat your heart out.

On a more serious note - does the pattern vary? I don't mean the location on the screen, or its overall size. From what I can see there is a repetitive block pattern.

[retiredcaps]

On Samsung TVs, when the caps fail, it's notorious for corrupting the EEPROM.

There may be a reset by shorting a couple of pins, but not entirely sure.

Like this?

http://www.badcaps.net/forum/showpost.php?p=305868&postcount=8

[katzohki]

Jackson Pollock eat your heart out.

On a more serious note - does the pattern vary? I don't mean the location on the screen, or its overall size. From what I can see there is a repetitive block pattern.

Yes, beside the fact that it tracks around the screen in "screensaver mode" the squares change a tad and pixels switch on and off. It doesn't seem like COMPLETELY random data, which is why I'm leaning towards the EEPROM as well...

On Samsung TVs, when the caps fail, it's notorious for corrupting the EEPROM.

There may be a reset by shorting a couple of pins, but not entirely sure.

Like this?

http://www.badcaps.net/forum/showpost.php?p=305868&postcount=8

I've seen that, but when I press menu it is scrambled too. I want to try it, but I can't confirm the OSD menu! I guess maybe I can try to sort of guess my way through it...

[Dave Turner]

I couldn't do it now, 'cos I don't know the system but back in the day of 8 bit micros you could sort of read the pattern in hex. Whilst more complex the same holds true now.

In this instance the question is whether a stable pattern helps point to the solution or is it irrelevant?

[Rasz]

My main monitor is a Belinea 21' that does similar thing on VGA , but works perfectly on DVI. When on DVI and with 1:1 mapping video is bypassing scaler completely. Try dvi before going further, even with corrupted flash or bad memory there is a chance it will work.

http://www.d43d.ru/forums/index.php?/gallery/image/1357-samsung-215tw/
http://img03.taobaocdn.com/bao/uploaded/i3/T1M9Y0XoNkXXaoqCvb_094912.jpg
http://remont-aud.net/_fr/86/4958775.jpg

as for the fault I dont think its flash, even solid background is corrupted on your picture. Check lvds cables, freeze/heat/tap ram chip.

[tautech]

I got given a nice little widescreen 24" TV that had a similar complaint, saved from a skip on a hunch.
Problem was found when data cable to LCD was removed and re-seated. 
Still going strong 2 years later.