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LCD computer monitor repair help

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LAN_403

Zum Beispiel

Thu Apr 02 2009, 10:25PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

I wasn't quite sure where to put this, so feel free to move it.

I dug a LCD monitor out of the trash the other day. It's a IBM ThinkVision L171 17" display, manufactured in 2005. Upon pluggin it in I was surprised to see it show the IBM logo and then "No Input signal." Everything is looking good.

However, when connected to a computer, upon start up it shows a few lines of text, the usual things you see when a computer is booting up but, after a second or so, it turns into a jumbled mess. This happens when more stuff starts coming on the screen. The display goes black (the backlight is still on), then the random mess comes back for a second and then the screen goes back to black. This cycle repeats over and over and seems random. You can still make out letters or even lines of text from the mess, though.

The power supply board had a load of bulged and/or leaky caps, which I replaced (I re-capped the whole board) hoping to fix the problem, but it didn't help. There are no other obvious signs of damage. The 12V output reads 12.5V and the 5V output 5.1V.

I realize the display is probably done for, but If anyone has any ideas, I'd love to hear them. My current CRT monitor is a POS and I'd really like to replace it with a LCD display (But I'm not going to go out and buy one

).

Soo, any ideas?

Chris Cristini

Fri Apr 03 2009, 02:13AM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

That sounds like refresh rate take a monitor that will work on the computer you are using and lower all of the resolution and refresh rate if this does not work I don,t know

Steve Conner

Fri Apr 03 2009, 07:30AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If it takes 12V and 5V, try running it off a different power supply. Wire it up to your computer's 12v and 5v rails or whatever.

If this fixes the problem, you know the fault is in the power supply. If it doesn't, you know the fault is in the mainboard, or the horrid flexi-chip thing in the LCD.

I doubt refresh rate would be a problem, a 2005 monitor will have DDC, so it can tell your OS what refresh rate and resolution it wants. Unless you're running some old Linux that doesn't support it.

Oh, also check the VGA socket/cable to make sure all the contacts are good.

Conundrum

Sat Apr 11 2009, 07:37PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

could be dodgy caps...
-A

Steve Maurer

Sun Apr 19 2009, 01:22PM

Registered Member #133 Joined: Fri Feb 10 2006, 10:27PM
Location: Pensacola, Florida
Posts: 47

Intermittent problems are tricky, but it could be a broken solder joint on the board assembly. This frequently occurs in electronic equipment due to normal thermal expansion / contraction during use. Look for hairline cracks in the solder around component leads. As solder cracks are hard to find, a magnifier is definitely helpful for the task.

A can of freeze spray is helpful in pinpointing broken solder joints. Use the freeze spray on small sections of the board until the problem appears / disappears with the application of the spray. Subsequently look for solder problems in the vicinity of the area that was sprayed.

You may also locate solder cracks by lightly tapping on the board with an insulator while the board is running. The back of the insulated handle of a screwdriver works well for this.

The last method to correct for poor solder joints is to re-solder complete sections of the board until the problem disappears. Pick a section of the board, re-solder it, and then turn on and check the device. If the problem still exists, then go to the next section and re-solder it. This should be used as a last resort, as it is obviously tedious.

Regards,

Steve

Zum Beispiel

Sun Apr 19 2009, 04:01PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

Thanks for all the input. I recapped the whole powersupply board, that had bulged caps, but that didn't help. I also went through the solder joints and resoldered some of the more dodgy joints, but no change.

The bad caps probably made the PSU give out a higher voltage than was intented, and that damaged the more sensitive electronics. So in short, I think the display is done for.

Oh well, it was worth a shot.

Dr. Dark Current

Sun Apr 19 2009, 04:31PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

When I was something like 12 I repaired a TV by taking a soldering gun and reflowing all of the solder joints. Turned it on and it worked. Something to try when you have nothing to do :)

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