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Re: [TI-99/4A] TMS9928 Project

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  • Sullivan, Bill
    I ve noticed that there is a DC voltage level for each of the component video signals. I ve also noticed that the input of the component video to RGB
    Message 1 of 147 , Jan 2, 2008
      I've noticed that there is a DC voltage level for each of the component
      video signals. I've also noticed that the input of the component video
      to RGB converter circuit adds DC voltage levels to the input signals,
      but the output to an RGB display is capacitively coupled. Could it be
      that the component video signals need to be decoupled from the DC
      voltage before connecting to a component video display? Anyone know the
      answer?

      Bill

      Sullivan, Bill wrote:
      >
      > After removing the TI circuits that were "hanging-on" to the "Y" output
      > I can only report no improvement. I had hoped that the TI circuits were
      > loading the "Y" signal down more than they should, and because component
      > video uses differential signals I thought this could be the "out of
      > range" issue.
      >
      > The monochrome output, "Y" signal, to composite video is still very good.
      >
      > Bill
      >
      > Sullivan, Bill wrote:
      > >
      > > Tursi,
      > >
      > > Thanks. The composite monochrome output works great!
      > >
      > > Bill
      > >
      > > Sullivan, Bill wrote:
      > > >
      > > > Hi Tursi,
      > > >
      > > > Not really. I used the strapping options shown on the schematic to
      > > > disconnect from most of the TI composite output circuit, but I
      > intend to
      > > > cut out some more as there are some circuits "hanging on" that might
      > > > load down the "Y" output.
      > > >
      > > > I can easily try your suggestion for composite black & white output.
      > > > Later today I hope.
      > > >
      > > > Bill
      > > >
      > > > Tursi wrote:
      > > > >
      > > > > > high, nor do I have the instruments to determine the signal
      > level of
      > > > > > R-Y, B-Y and Y. A multi-meter is inadequate for this purpose.
      > > > > > Any suggestions as to how to proceed from here?
      > > > >
      > > > > Good stuff, Bill! Are you actually reusing parts of the TI output
      > > > > circuit, then?
      > > > >
      > > > > I would suggest taking just the Y lead, and hooking it to an
      > ordinary
      > > > > composite monitor. You should get a good black and white signal.
      > Start
      > > > > there, anyway, and you can make sure that the chip and your output
      > > stage
      > > > > on that pin is good. I was able to get a picture off that pin even
      > > > > without anything in between.
      > > > >
      > > > > I'm going down a different path - I'll be producing SVideo. It's not
      > > > > quite as good as component/RGB but it's pretty close, and much
      > better
      > > > > than composite. I've sketched out the circuit I need but I won't
      > have
      > > > > time to work on mine for a while.
      > > > >
      > > > >
      > > >
      > > >
      > >
      > >
      >
      >
    • Kanton Levine
      Thats too bad.. I too, had been hoping that the component output could be proven, and was in fact hoping to someday have a component or S-Video TI-99/4A. Still
      Message 147 of 147 , Jan 21, 2008
        Thats too bad..

        I too, had been hoping that the component output could be proven, and
        was in fact hoping to someday have a component or S-Video TI-99/4A.

        Still its exciting that people are still working on this!

        --- In ti99-4a@yahoogroups.com, "Sullivan, Bill" <sullivanbill@...>
        wrote:
        >
        > I have a schematic and parts for the component to RGB converter on
        > hand. I intend to go forward according to the plan I did two
        months
        > ago. I just had high hopes of testing the component video output
        of the
        > TMS9928 before doing the RGB part. That hasn't worked out so well,
        so I
        > will go straight to the RGB conversion part without proving that
        the
        > component video is functioning as it should.
        >
        > Bill
        >
        > Tursi wrote:
        > >
        > > Well, it is... the US console ships with a 9918, which outputs
        composite
        > > video only. Except for three pins (video and genlock support on
        the 9918
        > > and YUV on the 9928), it's pin compatible, so Bill and I are both
        > > working on independent solutions using the 9928 to get better
        quality
        > > video out of our US consoles. :)
        > >
        > > The UK console ships with the 9929 which is the PAL version of
        the 9928.
        > > Maybe someone who thinks their PAL console has too sharp a
        picture would
        > > like to drop in a 9919, which is the PAL version of the 9918, and
        > > degrade their system to mere composite video? ;)
        > >
        > > 9918 - Composite video, NTSC
        > > 9919 - Composite video, PAL
        > > 9928 - Component video, NTSC
        > > 9929 - Component video, PAL
        > >
        > > Bill, do you maybe want to take the same route as the guy at
        AtariAge
        > > did, and use an arcade conversion circuit? According to the
        article at
        > > http://my.stratos.net/~hewston95/RTM42/RTM42.html,
        > > <http://my.stratos.net/%7Ehewston95/RTM42/RTM42.html,> he ended
        up
        > > using the
        > > RGB interface circuit from Baby PacMan, which also had a 9928.
        The board
        > > is called a "Vidiot". He says:
        > >
        > > "I checked eBay and there was a broken-for parts only Vidiot
        listed
        > > there, with only one bidder with a day to go. I put in a snipe
        and won
        > > it the next day for $12! Woot!
        > >
        > > It took about 10 days for the Vidiot to arrive, but when it
        finally did,
        > > I immediately wired it up with test clips, but got nothing. I
        checked
        > > the voltages with the volt meter and they were all wrong. It
        turned out
        > > the voltage filter section of the board was bad, so I just
        bypassed it
        > > and fed +12vdc into the circuit right before it got converted to
        +8.2vdc
        > > by a big resistor (according to the schematics). That gave me an
        image,
        > > but it was not synced. There were pots (knobs - variable
        resistors) on
        > > the board which were labeled Red, Green, Blue and Sync. I fiddled
        with
        > > the sync pot and got a stable picture! The color was horrible and
        > > bleeding badly. I fiddled with the color pots and got decent
        colors but
        > > still with terrible bleeding. I measured the voltage where it
        should
        > > have been +8.2vdc but it was only +7.6vdc. I checked the
        schematics and
        > > they showed the resistor which brought the voltage down to
        +8.2vdc was
        > > only 52 ohms. I grabbed a 1k ohm pot I had laying around and
        replaced
        > > the resistor with that. Then I adjusted it until the voltage read
        > > +8.2vdc exactly. I looked up at the monitor and was greeted with
        a nice
        > > crisp image! I fiddled with the color pots a little more and got a
        > > perfect, beautiful picture. I was in bliss."
        > >
        > > He goes on and shows (with pictures!) how he cut the video
        conversion
        > > circuit from the larger vidiot board and mounted it inside his TI.
        > >
        > > For my own issue, I learned about how S-Video really works and
        that
        > > snagged my plan. I did find with the help of schematics from the
        > > ColecoVision and Spectrum systems that an LM1889 video modulator
        should
        > > give me what I need, but I haven't tried it yet.
        > >
        > > ----- Original Message -----
        > > From: "mark wills" <markrobertwills@...
        > > <mailto:markrobertwills%40yahoo.co.uk>>
        > > To: <ti99-4a@yahoogroups.com <mailto:ti99-4a%40yahoogroups.com>>
        > > Sent: Saturday, January 05, 2008 3:23 PM
        > > Subject: Re: [TI-99/4A] TMS9928 Project
        > >
        > > >I thought the European one was different, hence my suggestion to
        Bill.
        > > >Sorry Bill if I'm talking rubbish and muddying the waters even
        more...
        > > >Hmmmmph!
        > > >
        > > > Mark
        > > >
        > > > Mark Wills, MSc MIAP
        > > > http://www.markwills.co.uk <http://www.markwills.co.uk>
        > > >
        > > > ----- Original Message ----
        > > > From: Tursi <yahoogroup@...
        > > <mailto:yahoogroup%40harmlesslion.com>>
        > > > To: ti99-4a@yahoogroups.com <mailto:ti99-4a%40yahoogroups.com>
        > > > Sent: Saturday, 5 January, 2008 10:20:47 PM
        > > > Subject: Re: [TI-99/4A] TMS9928 Project
        > >
        > > > The 9928 and the 9929 are essentially the same chip - 9928
        > > > is NTSC and
        > > > 9929 is PAL. Both output the same type of component signal.
        > > >
        > >
        > >
        >
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