Video Problem

Store Forums Hackvision Bugs/Problems Video Problem

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    Just built the kit this morning. Powers up OK, I get the bleep through the TV when I plug the power supply in and I get some picture – but it’s like when your TV is out of tune, the image isn’t stationary and kind of scrolls down the screen. If I hit the red button it goes into the game and I get the sounds, it’s just the image won’t ‘fix’. I’m in the UK, and I’ve soldered the PAL jumper. My TV is relatively new (two years old or thereabouts). I’ve tried another TV and get the same issue.

    Any ideas?


    Hmm, that’s very strange. I have not heard of that behavior before, and Hackvision was tested on PAL TVs in the UK (and I have lots of PAL customers). It’s especially strange that you see this behavior on 2 different tvs. Is the image stable and clear, but just scrolling vertically? Or is it unstable horizontally and all messy?

    You could try soldering the 75 ohm resistor in place, but I kind of doubt that would fix it. Do you have access to any other TVs?

    Also, do you have a USB-Serial programming cable? If so, we could change some video timings and recompile.


    Hi, yes it’s unstable horizontally as well. It’s not a steady scroll either, it varies in speed. Yeah, I do have a serial cable. I can give it a try at my sister in law’s, they’ve got a different TV brand? I’ll try that first and then give you a shout back.



    Success – of sorts! I’d got a second kit to give to my brother in law, who’s a retro gaming fan. Built up the second kit and it’s working perfectly. So I must have done something wrong with the first kit? Never mind though, great kit and great fun both to build and now play!


    Yes, well that does indicate that something is wrong with the first assembly. Perhaps you can carefully check some things like:
    – your soldering joints. Especially the resistors and diodes in the upper right of the board. The video behavior you describe indicates there could be a short.
    – are your diodes installed in the correct direction?
    – did you put the adhesive backing on the board? If not, the timing gets messed up if you touch the board near the crystal.
    – can you check the solder connections near the crystal and 22pF capacitors? That could mess up timing.

    Please feel free to send me high res photos of the board. I’m happy to look it over.


    I’m actually having the same problem – PAL TV in Australia.

    Everything works, I can start the board, audio starts but the screen picture does not stop rolling.

    I’ve tried a few things:

    a) Tested by uploading other code – using the Controllers library I can send serial data back to my PC and use the HackVision as an external controller [with OSX via python scripts, was fun!]

    b) Tried modifying the PAL as per ( Find _PAL_LINE_STOP_VSYNC, in /Applications/ – replace 7 with 2. )

    c) Tried messing around with other values available on the net for PAL in the above mentioned file

    //Timing settings for PAL
    #define _PAL_TIME_SCANLINE 64
    #define _PAL_TIME_OUTPUT_START 11

    #define _PAL_LINE_FRAME 312
    #define _PAL_LINE_START_VSYNC 0
    #define _PAL_LINE_STOP_VSYNC 7
    #define _PAL_LINE_DISPLAY 260

    For the life of me, I cannot get VSYNC to lock on with this PAL TV.

    I haven’t tried it with another TV yet, though considering thebot’s post here I’m beginning to wonder if there’s a defect in the crystal / atmega I’ve got on the board. I’ve doublechecked all of the solder points and searched for burn marks anywhere but I cannot find anything wrong.

    Before I go out and try and just purchase the board again I was hoping you might have any other ideas?


    I’m very sorry about the slow reply — I’m having problems with spammers on my forum, so legitimate posts are getting overlooked.

    I think you should try another TV. Per the original author of TVout, the vsync implementation does not exactly conform to standards, so he expects the vsync to not work with a small number of TVs. This is the first I’ve heard of someone actually experiencing this problem, though, and I suspect that other TVs may work fine.
    I also suspect your soldering is fine.

    If you really think it’s the crystal, you could try replacing just that component. 16MHz crystals should be readily available.

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