Test with HDMI to VGA adapter

[osresearch]

A mini-HDMI to VGA adapter should produce decent video on one of the channels and might eliminate the need for the LVDS device tree mess as well as the r2r dac. It's not quite as hackish, but might make a more stable video as well.

The kernel mode setting would need to hard code the 640x480 @ 60 mode and the hsync/vsync pins would need to be routed out of the VGA adapter.

[holzachr]

Works fine for me with an 8 $ HDMI to VGA converter. The color signals can be joined using 3x 47 (43 said to be even better) ohms resistors right before going onto the MDT's PCB.

When using a Pi, the following /boot/config.txt entries might be useful:

disable_overscan=1    // Use full screen size
hdmi_group=2          // Use DMT mode
hdmi_mode=4           // 640x480@60 Hz

[holzachr]

Using a network of 1x (in-line) or better 2x (voltage divider against ground, but watch out for shorts) 200 ohms potentiometers for each color to join the signals gives even better, more balanced video results.

To adjust, tune up the MDT's brightness and show a picture of the three RGB colors, demonstrating their additive mixing, in fullscreen. Use the potentiometers to achieve an equal brightness for all three base colors as well as for all three areas where two base colors are mixed: