VGA red input lost

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  • December 9, 2020 at 11:06 AM #43565
    totoche_b
    Participant

      Hi,
      I lost the red vga input signal, i checked my dreamcast VGA cable directly on a monitor (no problem), seems to not be the only one with this problem, is there anything to check before changing TVP7002PZP ? (or buy a new unit…)
      I tried to reset setting, downgrade to 0.86 (I saw the problem just after upgrading to 0.88), i also tested the signal from the VGA connector to R1.
      Best regards

      December 12, 2020 at 11:35 AM #43629
      marqs
      Participant

        It might be that TVP7002PZP has got damaged. Did you hotplug VGA cable any time the board was on?

        December 12, 2020 at 2:44 PM #43637
        totoche_b
        Participant

          I did not hotplug VGA cable last time i used the OSSC… I did not used it for months and few days ago i powered it up, do software upgrade from .86 to .88 and plug my dreamcast… other inputs seems to work

          December 30, 2020 at 6:00 AM #44080
          Morpheus_79
          Participant

            Seems to be a common problem for Dreamcast owners using the VGA input of the OSSC: sometimes the red output level of the Dreamcasts VGA signal “kills” the according input on the TVP7002 of the OSSC. There are several threads on this forum reporting this issue. I even replaced the TVP7002 myself for someone having the same issue… and the problem was gone.

            December 31, 2020 at 11:26 AM #44112
            marqs
            Participant

              I wonder if the issue has more to do with Dreamcast output than the fact that other video inputs go through THS7353 buffer which probably has better protection. Is there perhaps a large DC offset on Dreamcast RGB lines – not that it should matter in steady state as the signal is AC coupled on cable and before ADC, but could theoretically cause a spike on powerup. Speaking of that, I recall fixing an early version Kuro VGA module which had one channel routed directly to VGA output without going through respective AC coupling cap. Probably unrelated to this issue, but which VGA cables / modules did you use?

              February 19, 2021 at 1:01 PM #45384
              Morpheus_79
              Participant

                I’ve been involved in some discussion on another forum regarding the same issue. One user did some research in the past. He was in contact with the ‘Beharbros’ (since he bought the Toro Box for his Dreamcast from them). According to them the problem seems to affect only older vga boxes from the Dreamcast era (HKT-8100 maybe???). Newer Boxes shouldn’t be affected. Sadly they didn’t get into any details at what EXACTLY causes it.

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