Color Classic Mystic VGA Mod Strange Resolutions Results

[mcbeav]

I have a mystic color classic I purchased from another person. I was told no hardware modifications were done, and ResEdit was used to enable the LC575 board to work with the CC. I followed the VGA mod outlined on powerpc.org. I did both the sense line mod and the horizontal deflection mod, and confirmed continuity. I do have a revision D analog board, so there is no J78 jumper. I had to isolate pin 20 by cutting the trace. I did confirm it is isolated properly. With a clean install of Mac OS 8.1, curiously I have 3 resolutions available, none of which are the desired resolution the VGA mod is supposed to achieve. In the photo attached you can see 512x384@60Hz | 640x480@67Hz | 832x624@75Hz. Can anyone help direct me to what would be causing these results?

 

[mcbeav]

I have a mystic color classic I purchased from another person. I was told no hardware modifications were done, and ResEdit was used to enable the LC575 board to work with the CC. I followed the VGA mod outlined on powerpc.org. I did both the sense line mod and the horizontal deflection mod, and confirmed continuity. I do have a revision D analog board, so there is no J78 jumper. I had to isolate pin 20 by cutting the trace. I did confirm it is isolated properly. With a clean install of Mac OS 8.1, curiously I have 3 resolutions available, none of which are the desired resolution the VGA mod is supposed to achieve. In the photo attached you can see 512x384@60Hz | 640x480@67Hz | 832x624@75Hz. Can anyone help direct me to what would be causing these results?

I suspected that possibly the jumper mod on the logic board was done which was maybe causing the issue and causing the 512x384@60Hz to show as an option, but it doesn't appear that the mod was done. There is a resistor on R116, and no resistor on R109 or on R110. I've attached a photo of the area of interest on the logic board.

I'm missing something here, and pretty desperate for some help.

 

[codevonlux]

Your photo shows original LC575 resistor locations. 0ohm on R116 and no resistor on R109. It should work fine with the analog board mod.

You would only need to modify those resistors, OR ResEdit to make LC575 board work with an Unmodified color classic analog board.

A proper VGA mode should have 60Hz on 640x480. 67Hz indicates a possible Hi-res display is detected.

 

[codevonlux]

I still believe there is something wrong with your sense line mod in analog board. Could you take a picture on that area?

For VGA Mode you have to connect Sense Line 0 and Sense Line 1 to each other, while Sense Line 2 is left unconnected. For HiRes Mode you have to connect Sense Line 0 to ground and leave Sense Line 1 and 2 unconnected.

Pin 20 is Sense Line 2
Pin 24 is Sense Line 1
Pin 25 is Sense Line 0

 

[mcbeav]

I still believe there is something wrong with your sense line mod in analog board. Could you take a picture on that area?

For VGA Mode you have to connect Sense Line 0 and Sense Line 1 to each other, while Sense Line 2 is left unconnected. For HiRes Mode you have to connect Sense Line 0 to ground and leave Sense Line 1 and 2 unconnected.

Pin 20 is Sense Line 2
Pin 24 is Sense Line 1
Pin 25 is Sense Line 0

Thank you for the reply and the help, here are some photos, I applied solder mask to the traces that I cut, but I can remove that solder masks and take new photos that would help, please let me know. Thank you.

I have no J78 jumper as you can see in the photo, so in order to isolate pine 20, I cut the trace the is the white line coming out from pin 20. I isolated pin 25 by cutting the trace above the pin and below the pin. Then I soldered pin 20 to 24. I'm obviously missing something here.