archive.worldofdragon.org

Hello,
having seen that the board is from Dragon Data, I have searched my PC Dragon folders and finally I have found a very good schematics from P.Harvey-Smith dated April 2010.
I will enclose it here, hope this will be correct. It seems to be a way to better the image synchronisation on the MC6847.
The JP1 point on the schematics is the red wire on the photos I have attached on my last message.
It links to the /FS pin of the MC6847, so both /HS and /FS are used on this daughterboard.

Regards
Pere

Has anyone tried to see how much of a difference the card makes on the image quality?

I'd be a bit surprised if it affected image quality really, as all those are inputs to the SAM. Probably more like timing stability - I vaguely remember reading something about early CoCo 1s not working quite right because the HS pulse duration varied with heat, and a solution like this fixed it. Don't recall what the problem was though.

As Steve (Zephyr) mentioned earlier in the thread, this board has been discussed before. Phill (Prime) reckons that it cleans up the video signal.

Fair enough - I wonder how? Maybe buffering the inputs to the SAM reduces the drain on the signal being fed to the video output parts of the board.

It's just struck me whilst looking at the Dragon 64 circuit diagram, that the board was obviously an improvement as it's included in the Dragon 64 circuitry (IC14 & IC13A).

Just looking to maybe try and convert my Atom RGB board to work on the Dragon & CoCo, would not be a problem if the 6847 was socketed

Cheers.

Phill.