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    Thread: Taito Space Invaders. Rolling screen.

    1. #1
      aaablettt's Avatar
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      Taito Space Invaders. Rolling screen.

      Hi Guys,
      I have a rolling screen no matter what monitor I use. Any ideas?


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      Last edited by aaablettt; 6th August 2017 at 08:56 AM.

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      As i understand it rolling can be a v-sync problem. Does the output to the monitor have seperate h-sync and v-sync or a composite sync? Generally you can tell by the number of wires, 5 wires for composite sync (RGB, GND, Sync), 6 wires for seperate sync (RGB, GND, v-sync, h-sync).

      Also do you know which board type you have? And do you have access to an oscilloscope?

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      Quote Originally Posted by crackedMagnet View Post
      As i understand it rolling can be a v-sync problem. Does the output to the monitor have seperate h-sync and v-sync or a composite sync? Generally you can tell by the number of wires, 5 wires for composite sync (RGB, GND, Sync), 6 wires for seperate sync (RGB, GND, v-sync, h-sync).

      Also do you know which board type you have? And do you have access to an oscilloscope?
      Thanks for chipping in.
      This board set outputs a composite video so no sync wire at all. Just a ground and a video composite. I have swapped monitors and got the same issue then I swapped motherboards and issue ceased.
      No oscilloscope, just a logic probe.


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      Quote Originally Posted by aaablettt View Post
      Thanks for chipping in.
      This board set outputs a composite video so no sync wire at all. Just a ground and a video composite. I have swapped monitors and got the same issue then I swapped motherboards and issue ceased.
      No oscilloscope, just a logic probe.
      Aussie Arcade
      Ah, right. Not sure exactly what board you've got, but if its the L shaped one I've had a look at the schematics and the first place I'd start looking is an 74LS55 IC named 6B on the schematic. Try the logic probe on pins 1-4 and 10-13 and see if any of them are stuck high or low. The output of that IC (pin 8) is marked as "Comp Blanking" so a reasonable place to start.

      I'm assuming aside from the vertical rolling the image is otherwise fine?

    5. #5
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      Quote Originally Posted by crackedMagnet View Post
      Ah, right. Not sure exactly what board you've got, but if its the L shaped one I've had a look at the schematics and the first place I'd start looking is an 74LS55 IC named 6B on the schematic. Try the logic probe on pins 1-4 and 10-13 and see if any of them are stuck high or low. The output of that IC (pin 8) is marked as "Comp Blanking" so a reasonable place to start.

      I'm assuming aside from the vertical rolling the image is otherwise fine?
      Yes, the image is fine otherwise.
      I have probed around 4F and 6B. Nothing obvious but I'll go again.
      Cheers.


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      Hi Jimmy. What type of board is it?

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      L shaped.


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      Taito Space Invaders. Rolling screen.

      Changed out the 10mf cap.
      🤷


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      Quote Originally Posted by aaablettt View Post
      Changed out the 10mf cap.
      ��
      Did that fix it?

      If not... it looks like there are some lines that go high low at different frequencies. Some of the inputs to the blanking logic IC (6B) are these signals. Looks like they use the fact that they will all be high together at a certain interval (effectively dividing the lowest frequency by a 2^x number) to do some sort of timing. Checking those lines are pulsing at the right frequency would be helpful but i'm not sure how you can do that without a scope.

    10. #10
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      Quote Originally Posted by aaablettt View Post
      L shaped.


      Sent from my iPhone using Aussie Arcade
      How fast is the rolling? Annoyingly slow, fast flicker? I s the rolling consistent?

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