Color Classic VGA Mod Question

[GibLP]

Hi All,

I'm about to perform the VGA mod (Option 1) on a color classic analog board and ran across a discrepancy with my boards revision:

My board doesn't have J78 so the instructions say I have to disconnect (isolate) pin 20. However, at DD1, there appears to be a diode (M5C) where in the reference photo it's missing:





Any ideas on whether I need to remove this diode?

Thanks in advance

 

[GibLP]

I found another site listing a very similar mod: https://www.micromac.com/instructions/CC_Video_upgrade/index.html which keeps the diode intact. Only difference with this version is that it connects pin 20 and pin 3 instead of 20 and 24.

Any idea on which is "correct"?

Thanks.

 

[olePigeon]

@techknight wrote up an extensive mod over here:

Color Classic VGA Mod. the CORRECT way

I documented the changes to the Color Classic Analog Board to allow the board to operate at 640x480 without the transformer trace cut mod! Here are the CORRECT changes, this allows for full width without any distortions. CL9: Change from 3.3uF to 2.2uF 160V CL10: Change from 3.3uF to 1.8uF...

68kmla.org

Lots of discussion. I haven't done it myself, though.

 

[GibLP]

Thanks @olePigeon, I saw that thread but that method is quite a bit more involved than the one I’m trying. Besides, I have a Rev D board and its not totally clear what changes need to be made for that.

 

[GibLP]

Hi All. Anyone know what pin 21 does? I by mistake severed it while trying isolate pin 20. Is it a simple signal wire that I could use a bodge wire to fix or is it something more important that requires a thicker wire?

Thanks in advance.