Image starts the middle and off-center. Help?

[Themartianist]

Please see the attached video, sorry it's really crude, I recorded it using my phone's camera. Does anyone know how to resolve this issue?

[Steve Anderson]

I must admit I'm trying to work out what the display device is...and what the bright 'ring' at the top is?

But it would appear you have line and frame lock, it's just in the wrong place. More details of what you are using and the source of video would help greatly.

Steve A.

[Themartianist]

I attached some pictures and additional video with the correct orientation. The wheel and much of the electronics employed here come from the NBTV club shop with the exception of the power supply, that I purchased as a complete unit elsewhere. The view window is a dome-shaped 3 inch magnifying glass.

Now about the additional video attachment and so forth... I am displaying a 1924 recording of Calvin Coolidge converted to wav format using the Video2NBTV software. My computer is playing the wav file and outputting its signal through its headphone jack which is then split between the RCA inputs in the back of the TV. As you may notice with this new video I think I am closer to getting the starting line oriented properly. Only a small portion of what would normally be at the top of the screen is sitting at the bottom currently. I took the piece of black tape you'll see in one of the photos and simply moved it to another sync hole on the wheel and that white ring you saw in the first recording I showed you is the LED light shining through the remaining unblocked sync holes.

Another thing, do you notice how the lower part of the image has more detail than the top?? The top of the image has a lot of solid black lines and I have no idea why. Any guesses?

Now note well, I did not build this TV by myself. A couple of engineers helped me with it and one of them is an electrical engineer in particular so he handled most of the electrical aspects. So if you have any questions or comments about the specifics of the electrical setup please try to dumb them down a bit if you can and if I still don't know what you're talking about, I'll gladly forward your questions or comments to my electrical engineer friend who would be able to understand. Thanks!

[gary]

I think the distortion of the line widths is just the an artefact of the lens you are using - can you remove the lens temporarily to verify that? - other than that the picture looks great! You might like to put a mask in front of the disk so that you only see one image.

By the way it may not be obvious to you but you will see a string of images all around the disk (wherever the modulated led light falls on it). This is normal and it is customary to have a mask made to the size of one single image.

[Themartianist]

You're right it is an artifact and while I can't move the lens, I could move the wheel: the shelf to which it is mounted rests snugly in the cabinet so I gave it a few good nudges forward (while turned off!) and the image improved.

Yes I ultimately knew there'd be multiple images on the disk and as for a mask to single out the view to one of those images, that is a good idea, but I'm not concerned about that just yet. My problem is I don't know how to get one of those images to line up nicely in the center of lens. Instead the dividing line between two of them is at the center. Any ideas?

[Themartianist]

Well I've now determined it actually does not matter which sync hole I cover. The image will start at a different position every time I start a video. I.E. Causing some of the lines that should be at the top to be cut and pasted onto the bottom or vice versa. To me it seems it has something to do with how fast the wheel is spinning when the video starts and getting the wheel to top speed before starting a video seems to get the most consistent results. Trouble is you can't get the wheel to spin without playing the video SO you have to keep restarting the video until it gets to top speed!

So does anyone know how to get a ( at least somewhat) consistent image each time the TV starts without a whole lot of hassle? I plan to put this TV on public display and want it to be useable, but considering it takes hours to get a single video synced up and aligned properly, it seems entirely impractical to put this on display.

[gary]

Well your picture appears to be locked perfectly as the image itself is not split. Is the position of the sync bar (black line) *always* in the same position? (albeit offset from where you want it). If so then the problem would be that the position of the sync sensor is offset from the position of the picture aperture as it enters the picture frame. This is hard to explain in words but just imagine you had a mask in place then as a sync hole passes in front of your sync sensor then a picture aperture should *just* be entering the area exposed by the mask.

If that is impossible (likely) to understand then I would need to draw a diagram or something. Let me know.

[Themartianist]

Once the image settles/stabilizes, yes, that thick black bar is always in the same spot: right in the middle of the viewer and that's not the only problem I'm having. I decided to make some diagrams of my own so I don't have to describe exactly what I'm seeing.

You're welcome to send me a diagram too if you would like. I'm sure it would help.

[Steve Anderson]

It would appear that you're getting line sync (400Hz) but half a line out. This should be resolved by moving the sync-hole detector (or whatever you're using) half a line (basically half the inter-hole spacing approx.) on the disc.

Frame lock is another subject on its own, many have had problems with this. Often it's a case of fiddling with some of the component values on the motor-drive board. Others here will hopefully help better than I can in this regard.

Steve A.