Another Dragon version???

[pser1]

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.

Schematics from P.Harvey-Smith

Dragon Data pn48200.jpg (80.04 KiB) Viewed 3205 times

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

[tormod]

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

[sixxie]

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.

[Alastair]

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

[sixxie]

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.

[prime]

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.