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Video glitch / MARCH's Apple II

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  • Evan Koblentz
    Something s amiss with our only Apple II. The vertical hold is all messed up. Tried adjusting it; it stays put for a while and then moves around. Tried
    Message 1 of 6 , Nov 16, 2011
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      Something's amiss with our only Apple II. The vertical hold is all
      messed up. Tried adjusting it; it stays put for a while and then moves
      around. Tried different monitors and different video cables; same
      result. Even when it's not moving, the screen seems too big somehow. Any
      ideas for what could be wrong and how to fix it?
    • Matt Patoray
      Bad capacitor in the video output circuit, bust out the schematic and an ESR meter Sent from my iPhone
      Message 2 of 6 , Nov 16, 2011
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        Bad capacitor in the video output circuit, bust out the schematic and an ESR meter

        Sent from my iPhone

        On Nov 16, 2011, at 10:31 PM, Evan Koblentz <evan@...> wrote:

         

        Something's amiss with our only Apple II. The vertical hold is all
        messed up. Tried adjusting it; it stays put for a while and then moves
        around. Tried different monitors and different video cables; same
        result. Even when it's not moving, the screen seems too big somehow. Any
        ideas for what could be wrong and how to fix it?

      • Evan Koblentz
        ... Bill Deg. just made the same suggestion offline. That level of electronics diagnosis is (quite frankly) over my head. It can wait until all our experts are
        Message 3 of 6 , Nov 16, 2011
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          Bad capacitor

          Bill Deg. just made the same suggestion offline.

          That level of electronics diagnosis is (quite frankly) over my head. It can wait until all our experts are in town for the holiday party, or maybe some like Jeff J. or Nick can work on it before then.
        • nicodemus_nj
          On Monday, IXR is getting in a shipment of common-value electrolytic capacitors, so if you need a replacement, we can see if we have one that s close. -DW
          Message 4 of 6 , Nov 18, 2011
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            On Monday, IXR is getting in a shipment of common-value electrolytic capacitors, so if you need a replacement, we can see if we have one that's close.

            -DW
          • B Degnan
            First someone needs to determine with confidence exactly what is wrong. You don t want to start replacing capacitors willy nilly. The easiest way to start is
            Message 5 of 6 , Nov 18, 2011
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              First someone needs to determine with confidence exactly what is
              wrong. You don't want to start replacing capacitors willy
              nilly. The easiest way to start is to compare and contrast with an
              Apple IIplus that works.

              Bill

              At 11:49 AM 11/18/2011, you wrote:

              >On Monday, IXR is getting in a shipment of common-value electrolytic
              >capacitors, so if you need a replacement, we can see if we have one
              >that's close.
              >
              >-DW
              >
              >
              >
              >------------------------------------
              >
              >Yahoo! Groups Links
              >
              >
              >
            • Mike
              Video timing is entirely digital, final mixing of sync/color/video is done with the three resistors on the right side of the board. There is a bit more signal
              Message 6 of 6 , Nov 18, 2011
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                Video timing is entirely digital, final mixing of sync/color/video is done with the three resistors on the right side of the board. There is a bit more signal shaping done, but it would be unusual for this sort of problem to be caused by that.

                Most likely issue is in digital logic that generates the sync signal. The source of timing comes from the four 74LS161's on the motherboard that divides the base video clock into horizontal and vertical components.

                Also, make sure that the motherboard is not configured for PAL video, which mucks with video timing and could cause the vertical hold issues with NTSC monitors.

                Regards,
                Mike Willegal

                --- In midatlanticretro@yahoogroups.com, Evan Koblentz <evan@...> wrote:
                >
                > Something's amiss with our only Apple II. The vertical hold is all
                > messed up. Tried adjusting it; it stays put for a while and then moves
                > around. Tried different monitors and different video cables; same
                > result. Even when it's not moving, the screen seems too big somehow. Any
                > ideas for what could be wrong and how to fix it?
                >
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