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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sun May 03, 2009 8:03 pm Post subject: Zero H overscan on AmPro's??? |
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Has anyone figured out how to get zero horizontal overscan from a AmPro at 1080P? I can get zero top and bottom no problem but the best I can squeek out of the sides is about a 3 overscan. On screen this robs about two inches of usable video information from both sides. I did not even notice it until I used HD video essentials for the first time from my PS3.
PS Yet another in the list so far and few between "on topic" posts by me.
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Chip
A Barco is only a AmPro with training wheels
Card carrying member of the AVS chain gang.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Sun May 03, 2009 11:52 pm Post subject: |
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Chip,
Short of using a scaler to increase the horizontal blanking time to match the projector's horizontal retrace time there isn't alot that can be done. If one could get power mosfets that could handle 1800V pulses without breakdown you could replace the 1100V parts that are on the horizontal output board. I don't know of any parts like that. Electrohome put three 600V parts in series to get the capability to have a short retrace.
The Ampro projector has a minimum retrace of 2.8us. 1080p needs something less than 2us.
I'm going to give up one of my secret recipes for determining deflection parameters. I don't think it makes much difference now.
Attached are three scenarios for 2.8us, 1.8us, and 1.5us retrace times. Look at the last answer for the "flyback" voltage generated with the different retrace times.
Scott
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Mon May 04, 2009 5:54 am Post subject: |
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Whoa.
I only understand some of that...but whoa.
So you are saying, to push the beam back in under 2us, you need ~1800v applied to the yokes?
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Mon May 04, 2009 1:11 pm Post subject: |
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To retrace in 1.5us takes about 1800V. Yep. The voltage could be less with yokes of lower inductance. Voltage would go down, current would go up.
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Mon May 04, 2009 3:44 pm Post subject: |
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Doesn't that add more stress to everything?
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CRT.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Tue May 05, 2009 12:41 am Post subject: |
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Change the yoke inductance from 200uH (three in parallel gives 66uH) to 66uH, so the three in parallel are 22uH, and the current goes up from 21A peak to peak to 37App but the peak flyback voltage is now just over 1000V. I'll take that trade. Forget scanning at 15kHz, though.
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Tue May 05, 2009 9:41 am Post subject: |
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So how could we change the yoke inductance? or
could a daughter board be made off the horizontal board to hold the additional circuitry to provide the increased voltage required to reduce the retrace time?
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Chip
A Barco is only a AmPro with training wheels
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Tom.W
Joined: 09 Mar 2006
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Tue May 05, 2009 10:38 am Post subject: |
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I would but I'd have to sacrifice the reliability I enjoy now. 
But really, the only time you will notice the missing video information from the sides is when you are viewing test patterns.
I can't speak for everyone here (and I'm sure I don't) I don't spend up a set of tubes looking at test patterns.
I don't invite a bunch of people over to watch Digital Video Essentials. I think my wife would have me commited. 
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Chip
A Barco is only a AmPro with training wheels
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