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kevin_k
Joined: 25 Oct 2007
Posts: 67
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| Posted: Fri May 30, 2008 1:00 pm Post subject: Scoping xg1352 |
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Hoping someone can help with this
I'm working on the daughter pwb. When I remove the signal to adjust the VR812 set up pot I can't get the waveform to bottom out at zero. With the pot bottomed out it stops a 200mv away.
If I continue the scoping procedure and ignore this and move to the gain ctl pwb those wave forms continue to be high also.
I checked the power coming in and the power supply. Those are both clean. I've tried a different daughter board, same result.
What would be in front of this in the chain that would cause this.
Any ideas would be appreciated, thanks
Kevin
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sat May 31, 2008 4:18 am Post subject: |
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I'm sure you know you dont need to get to zero but less then 120mv. What's the amplitude like with a signal? Is the +9v source voltage off at all?
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kevin_k
Joined: 25 Oct 2007
Posts: 67
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| Posted: Sat May 31, 2008 4:48 am Post subject: |
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The japalenglish in the manual is say +\- .02 so I was working off that, but still with the pot bottomed out I'm a ways off of 120mv.
Amplitude is fine, that adjusts ok, but I appreciate the thought on the source. I didn't think of that. I'll check it tomorrow. I'm using a dvd player and I've read of some people having trouble using a dvd player as a source.
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kevin_k
Joined: 25 Oct 2007
Posts: 67
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| Posted: Sat May 31, 2008 3:57 pm Post subject: |
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I didn't think of it last night, but to adjust this pot there is no signal going into the projector. The manual says "when the signal is removed under the video display condition".
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sat May 31, 2008 4:12 pm Post subject: |
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| kevin_k wrote: | | I didn't think of it last night, but to adjust this pot there is no signal going into the projector. The manual says "when the signal is removed under the video display condition". |
Thats correct. I believe you misunderstood what I said. The +9 vcc is from the power supply which is usually referred to as source voltage. The circuit containing VR812 uses this 9v along with gnd to affect the ABL circuit in IC701. A variation in the 9v will cause improper signal adjustment. What is the problem as to why your adjusting these?
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kevin_k
Joined: 25 Oct 2007
Posts: 67
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| Posted: Sat May 31, 2008 4:52 pm Post subject: |
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I'm the intermediary. My neighbor is an ee and he's scoping it. He's at work and I'll check later today with him. We checked several different probes, he said he checked both AC and DC coming out of the power supply and they looked ok. But I'll show him your note.
Anything else you can think of we can check?
I replaced the v drive and put new g and b tubes in so we just started from the beginning to dial everything in. We didn't think it would take long so we did it to verify everything.
I appreciate it
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sat May 31, 2008 5:50 pm Post subject: |
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The 9v is actually derived on the daughter board along with the +5 and + 12 for that board. Since you say you tried a different board then you would have to check the +15v line from the power supply. I'm not sure why your concerned about this board because if I'm not mistaken, but not 100% sure, this board is only for composite and S-Video in which most will agree would be a waste for an XG1352, or any other projector that will scan higher then 480i.
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kevin_k
Joined: 25 Oct 2007
Posts: 67
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| Posted: Sat May 31, 2008 6:18 pm Post subject: |
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We're having trouble getting the pedastal down on the gain ctl pwb. Which is the next procedure after the daughter board. When we bring the pedastals down to approriate levels for each tube we lose the image. It seems to want to run hot, so our thought was, was that the daughter board was effecting it?? Don't know the chain, but the manual asks you to adjust the daughter board prior to the gain control board.
I have scoped this projector before and we got good results. We'll go over the power supply. I have a couple parts projectors so if need be I can slap a different power supply in.
Ultimately I'll use my htpc @ 1080i.
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Sun Jun 01, 2008 9:13 am Post subject: |
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It's really hard to get the pedestal levels right.
What you think you are setting it to may not the the right level.
You need to be able to see everything, so there'll be lots of junk in the scope screen, and you set the pedestal to a fuzzy little just visible line.
You'll know when it's right as the image will look right as well. And there will be no funny "back raster" showing at normal brightness levels.
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