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Forum Index : Microcontroller and PC projects : VT100 composite total loss of Vsync...
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9589 |
Hi - has anyone seen this with a VT100 terminal? Version 1.3, which I think is the latest? On a 9" LCD, there is no vertical sync at all, and the frame rolls vertically like mad. This problem is specific to the LCD, because if I put another LCD panel on it, it works just fine in PAL or NTSC modes, but on the 9" screen it goes bananas on either PAL or NTSC. The 9" LCD which won't co-operate, works just fine with a composite colour signal such as from a DVD or VCR output for example. I could email Geoff directly, but I put this up on the forums in case anyone else has seen this when they have been playing with the VT100 on LCD panels, and perhaps found a fix? I would like to use the 9" one if I could, but I can live with the smaller 7" one if I have to - whatever works, but I am curious as to why the 9" one is having a fit with the same signal.......  Smoke makes things work. When the smoke gets out, it stops! |
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Geoffg Guru  Joined: 06/06/2011 Location: AustraliaPosts: 3282 |
The problem might be caused by the display being sensitive to the details of how the video is generated. The VT100 firmware does not do proper interlacing but fakes it and perhaps the display is being confused by this. In my testing all displays coped OK but there could always be an exception. I cannot think of a solution to this one. Geoff Geoff Graham - http://geoffg.net |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9589 |
Hello Geoff. 
Thanks for chiming in. Yeah, I expect it is NOT an easy - or even possible - fix for this particular 9" display, which is a shame, as I would have loved to have used it cos of it's size. 
No big deal. The 7" one works, and all other displays I have tried all work in either PAL or NTSC. SOME LCD panels I have found don't like PAL, but when you switch to NTSC, they settle down and can be used. Most LCD's don't care either way though, but this 9" problem-child does. 
Not to worry - I was more curious as to what was going on more then anything else really, so we'll say it is the interlacing then. Smoke makes things work. When the smoke gets out, it stops! |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Composite.... Don't suppose feeding it in to & back out of some sort of external modulator would help. IE as a test pipe it into VCR in & then crab it from VCR out? Might prove something. Phil. |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2949 |
Grogs, Try using a small cap (experiment) on the sync line to GND (after the 470OHM).. It might delay the sync enough to make it work. Kind Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9589 |
Hi Mick.
Good idea - I will have a play around with that, and post back if successful. Smoke makes things work. When the smoke gets out, it stops! |
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