RF modulator replacement on the 264-series

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Sun, 24 Feb 2013 16:21:28 +0100
Message-ID: <512A2FF8.5020708@laosinh.s.bawue.de>
Hello,

a while ago I posted the circuit from the forum64 thread about what is 
needed in place of the RF modulator.

The original circuit was meant for a 6569 VIC and used a 470 Ohm pullup 
resistor in the luma driver. This is too small for a TED, the datasheet 
suggests 1 KOhm. If you use 470 Ohm, the picture is rather dark. I'd 
expect the same to be the case with the HMOS-II VIC (8565 if it's PAL).

So here's the adjusted circuit for TED, tested today, brightness is now 
OK on the C16 I tried it with:

Video amp for TED or VIC-II. To be used in place of the RF
modulator, generating better signal quality.

Note: This circuit removes the CVBS output! It's Y/C only!

                    ___ R1
   chroma in  -----|___|---+     +5V
                           |      |
                           |      |
                    R2     |      |
                    ___    |    |/
              +----|___|---*----|  T1
              |                 |\
              |   R4        R3    V
              |   ___       ___   |
              *--|___|--*--|___|--+
              |         |
              |         |        || C1
             ---        +--------||---------- chroma out
             GND                 ||


               D1       R5    +5V
                       ___   |
   luma in ---|<|--*--|___|--*-------------------+
                   |         |                   |
                   |         |                   |
                   |       |/                   ===  C2
                   +-------|  T2                 |
                           |\                    |
                             V                   |
                             |   R6        R7    |
                             |   ___       ___   |
                             +--|___|--*--|___|--*
                                       |         |
                                       |        ---
                                       |        GND
                                       |
                                       +--------- luma out


  T1 = T2 = BC547B
  D1      = 1N4148
  R1 = R2 = 510 Ohm
  R3      = 68  Ohm
  R4      = 270 Ohm
  R5      = 1 KOhm
  R6 = R7 = 150 Ohm
  C1      = 1nF
  C2      = 100nF

Do _not_ use metal film resistors, keep connections short.

luma in    = pin 23 on TED, pin 15 on VIC-II
chroma in  = pin 13 on TED, pin 14 on VIC-II

luma out   = pin 1 on video output
chroma out = pin 6 on video output


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Received on 2013-02-24 16:00:03

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