archive.worldofdragon.org

Sound and composite video signals are mixed in the UHF modulator (UM 1287, PSU board, schematic SA21204.ZIP), so the problem may be here or in the IC that generates the sound signal, IC20 (4529, schematic OKI322.ZIP). Have a look at the schematics here: http://archive.worldofdragon.org/archive/index...

Never heard of it before, I have no idea of what can it be

Most of the video signals come from the MC6847 VDG and only a few come from the MC6883 SAM. If both computers use the same Motorola chipset you could use the same circuit to add the color burst to the video composite signal. Do you know if it has a SAM?

Dragon 64L PAL Video Schematic v4

Update. Fixed some errors that I had fixed in a previous version but, for some reason, appeared again in v3. It seems to be related with library management in KiCAD. Sorry for any inconvenience.

I'm not sure, I haven't an oscilloscope to have a look at the signals. Particularly you should check how the output of the LM1889 is mixed with the B/W composite video signal. Perhaps you could use a simple switch to turn the output of IC9 on/off since the color burst is simply added to the composit...

BTW, I also have a very early issue Dragon 32 (piggyback board type) which has a video fault that causes a very bad flickering of the picture when 2 colour modes are used in combination with SCREEN 1,1. Four colour modes work perfectly, and 2 colour modes in combination with SCREEN 1,0 also work wi...

Yes, the colour display is very good. Desoldering the LM 1889 chip, or disabling the colour crystal (0.1uf capacitor in parallel as described in Dragon User, September 1988) results in a nice clear b/w display, but cutting the track from pin 6 of IC9 (LM1889) to R7 does not. http://dragondata.world...

...displaying a rather poor quality green screen display with no colour mmm, green?, can you see a B/W image?... it should be B/W. I have removed the LM1889 in my Dragon 64 and I can see a perfect clear image. However, the D64 video amplification stage is different to the D32 video amplification st...

The VDG (MC6847, IC12 on CPU schematic) generates the appropiated brightness and syncronizing signals to create a B/W composite video signal. The colour burst is generated by means of a LM1889 and added to the B/W composite video at the final stage. If the colour burst is not present you see a B/W i...

New Dragon 64K PAL Video Schematic v3 (see upload subforum) The schematic has been captured using the open source tool KiCAD. The shape of most of the parts has been redesigned to match the look of the Dragon Data schematic and included in a lib file. Although I have checked each part, line, ref and...