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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Wed Aug 25, 2010 4:23 pm Post subject: Panasonic PT-LB20U 3LCD projector repair question |
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I have two 3lcd projectors we pulled out of service. They do 720p/1080i. The picture they put out has become "discolored". I'm hoping I can repair at least one of them, or both cheaply. Other than the poor picture output they seem in good working order.
I searched and read an earlier thread (I know shocking right, who really does that, haha) and it looks like some tinted glass filter plates may fade over time. Are those replaceable? Where would one buy them?
The model of the projectors is Panasonic PT-LB20U. I'm hoping to find a service manual somewhere too.
http://www.projectorcentral.com/Panasonic-PT-LB20U.htm
Thanks!
dale
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Wed Aug 25, 2010 4:51 pm Post subject: |
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After more research it appears certain lcd panels can "go bad". You can replace the entire 3lcd assembly, dropping in a new one that's factory aligned. part number L3P07X will fit most .7" panel units. $150 is the cheapest I can find. oh well.
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JOneil
Joined: 05 Jul 2010
Posts: 47
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| Posted: Wed Aug 25, 2010 5:18 pm Post subject: |
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If the image is discolored its usually a polarizer. It could be a panel also but the percentage is usually higher on the polarizer. Take it apart and see. If you find out what is bad and can't find the part, post back and I'll check my sources.
Here is the manual. You have to use internet explorer to open it. Firefox wont work. Enjoy.
http://www.4shared.com/file/spomD9Yr/Panasonic_PT-LB20U.html
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Wed Aug 25, 2010 5:58 pm Post subject: |
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Thanks for the help! I'll open it up and check it.
dale
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Wed Aug 25, 2010 6:05 pm Post subject: |
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You need to figure out if it's discolored, or whether one of the LCD panels is bleeding. If you get say a blue haze over the entire picture, then the LCD panel is bad, and isn't turning off.
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Thu Aug 26, 2010 4:04 am Post subject: |
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ok, here's what I got. It appears that even in the dark areas of the screen where nothing should be projected I have a blue discoloration. Both projectors exhibit identical problems. thoughts?
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WanMan
Joined: 19 Mar 2006
Posts: 10270
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| Posted: Thu Aug 26, 2010 2:09 pm Post subject: |
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Any way for you to feed a non-Blue input? For instance, what happens if you feed a green signal, or a red signal? There is a dichroic splitter that separates the Cyan color into green, which passes directly through the dichroic combiner block, and blue. That picture does look like the LCD panel for the Blue is now always on.
_________________
Trust no one. Absolutely no one. Advice of the board.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 3:12 pm Post subject: |
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Yes thats an interesting image. Go into the service mode and cycle between the white, green red and blue screens and respond with what you see.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 3:33 pm Post subject: |
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| WanMan wrote: | | Any way for you to feed a non-Blue input? For instance, what happens if you feed a green signal, or a red signal? There is a dichroic splitter that separates the Cyan color into green, which passes directly through the dichroic combiner block, and blue. That picture does look like the LCD panel for the Blue is now always on. |
Wan, I believe this model doesn't have prisms or dichronic filters. It uses a PBS array.
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Thu Aug 26, 2010 3:39 pm Post subject: |
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Well the first problem is that it's upside down. 
This looks very similar to the two 2500 lumen Panasonics I had in from a pub once. Both units had the blue LCD panel die sometime in the second bulb lifespan. If that's it, it's not worth repairing.
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Thu Aug 26, 2010 3:49 pm Post subject: |
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OMG, that's why the movie looked weird, it's upside down! 
Curt, I think you're right, I think the blue panel is fried. Thanks for the info. I'll check it out more tonight.
Dale
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 4:27 pm Post subject: |
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Easy enough to tell if its a panel or not. Just swap the blue and the red and see if it follows.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 4:49 pm Post subject: |
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You know I just happened to think. Are you sure the blue setting in the menu is not cranked up to high. I didn't look to see what menu it is in as I didn't bother getting a user manual. Then just that funny line around the top would depend.
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ecrabb
Forum Moderator
Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Thu Aug 26, 2010 5:11 pm Post subject: |
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| macgyver655 wrote: | | You know I just happened to think. Are you sure the blue setting in the menu is not cranked up to high. I didn't look to see what menu it is in as I didn't bother getting a user manual. Then just that funny line around the top would depend. |
Doesn't look like just the blue turned up too high to me - that "funny line" pattern looks like it runs around all three sides that are visible, and is very organic and consistent with filter or panel dye decay.
Mac, with the PBS array arrangement, where are the primary wavelengths split/generated?
SC
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Thu Aug 26, 2010 6:36 pm Post subject: |
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just curious, if I can swap the lcd panel from one color to the next... could i take them from my spare projector? If each one has one bad panel then maybe I can make one work.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 6:45 pm Post subject: |
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| ecrabb wrote: | | macgyver655 wrote: | | You know I just happened to think. Are you sure the blue setting in the menu is not cranked up to high. I didn't look to see what menu it is in as I didn't bother getting a user manual. Then just that funny line around the top would depend. |
Doesn't look like just the blue turned up too high to me - that "funny line" pattern looks like it runs around all three sides that are visible, and is very organic and consistent with filter or panel dye decay.
Mac, with the PBS array arrangement, where are the primary wavelengths split/generated?
SC |
Yeah that funny line looks like a burnt polarizer but the polarizer shouldn't cause the over saturation. So thats why I thought maybe an overdriven panel. I thought if he could turn down the blue just to see what would happen. But could be a bad panel also like Curt said. Have to get in there to find out.
The PBS array is just a panel to separate the light into different paths and then to adjustable reflector mirrors. 1 PBS for all 3 colors and 3 mirrors, 1 for each color. I never read much about it as it didn't seem to be commonly used. At least from what I've seen.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 7:33 pm Post subject: |
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| akajester wrote: | | just curious, if I can swap the lcd panel from one color to the next... could i take them from my spare projector? If each one has one bad panel then maybe I can make one work. |
The panels are different but you should be able to swap them just for testing purposes.
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drice1234
Joined: 07 Oct 2006
Posts: 1309
Location: Allen, Texas
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| Posted: Thu Aug 26, 2010 8:49 pm Post subject: |
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Not to hijack but Mac I still have those 2 Panasonic LCD's with this same issue we had discussed previously. Are you going to be in the Dallas area anytime? They are kinda heavy (30 lbs ea.) so probably not worth the shipping to you. If you don't have plans to be around here I will probably toss them
Thanks
Dan
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Aug 26, 2010 8:56 pm Post subject: |
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| drice1234 wrote: | Not to hijack but Mac I still have those 2 Panasonic LCD's with this same issue we had discussed previously. Are you going to be in the Dallas area anytime? They are kinda heavy (30 lbs ea.) so probably not worth the shipping to you. If you don't have plans to be around here I will probably toss them
Thanks
Dan |
Dan. No I wont be out that way anytime soon but if your going to toss them I might pay the shipping to me. Shoot me a PM if thats an option.
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ecrabb
Forum Moderator
Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Thu Aug 26, 2010 9:30 pm Post subject: |
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| macgyver655 wrote: | | Dan. No I wont be out that way anytime soon but if your going to toss them I might pay the shipping to me. Shoot me a PM if thats an option. |
Hey, if you're going to toss 'em, and Mac, if you don't want two of them, I'd pay to ship the other one. I'm still looking for a "neighborhood movie night" projector and this would make an interesting winter project.
Thanks,
SC
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