I got the sample boards from JLCPCB for what I had called C64-JBgone, and after testing, it did clean up the video, but the jail bars although lighter could still be seen against darker backgrounds. So I accept that this must be coming from inside the VIC-II chip, and because of this there really is no way to completely eliminate this effect. I believe Adrian Black from Adrian's Digital Basement came to a similar conclusion after much experimentation of his own.
And I also played around with some of the ideas embodied within the LumaFix64 mod, but found that approach to be lacking in overall effectiveness, and in certain situations making things even worse.
I'm pretty content with the progress I made via improved video circuit design and better shielding. However the over scan and white line problem visible on the left was in need of a solution, so a new plan was formulated, and that plan is the C64-VGATE VIC-II Video Board.
And I also played around with some of the ideas embodied within the LumaFix64 mod, but found that approach to be lacking in overall effectiveness, and in certain situations making things even worse.
I'm pretty content with the progress I made via improved video circuit design and better shielding. However the over scan and white line problem visible on the left was in need of a solution, so a new plan was formulated, and that plan is the C64-VGATE VIC-II Video Board.
Click Image to Enlarge
I took what I had learned in the previous design, which had a lot in common with the first version C64 motherboard video output circuit, and then streamlined it before adding what I call VGATE technology. Which in a nutshell blanks out a specified amount of over scan (what was never meant to be seen) either from the left or right side of the screen, or in some cases like on the Atari - both sides. So for the C64, over scan only occurred on the left side of the screen with a thin white line visible on the extreme left when viewed on an LCD wide screen monitor. The white line was something new to me, but would be cured by the over scan blanking I was implementing.
The Video Gating (VGATE) where the blanking occurs, is controlled by a PIC microcontroller that derives its clock from the VIC-II Dot Clock on pin-22 (multiplied by 4 inside the PIC with a PLL), and then gets synced at the beginning of every line by the video's CSYNC signal. This gives us very precise control of where and when the gating signal gets turned on or off, and where it flips the analog switches to an OFF state in order to stop the video from displaying. The code for the PIC's firmware needed to be fast, so the source was written in assembly language and then GPASM was used to compile the Microchip PIC machine code, creating the hex file for flashing the chip. The asm text file was written and saved on a Linux box, so there may be issues with the end of line in Windows, although it should be viewable in most browsers.
The Video Gating (VGATE) where the blanking occurs, is controlled by a PIC microcontroller that derives its clock from the VIC-II Dot Clock on pin-22 (multiplied by 4 inside the PIC with a PLL), and then gets synced at the beginning of every line by the video's CSYNC signal. This gives us very precise control of where and when the gating signal gets turned on or off, and where it flips the analog switches to an OFF state in order to stop the video from displaying. The code for the PIC's firmware needed to be fast, so the source was written in assembly language and then GPASM was used to compile the Microchip PIC machine code, creating the hex file for flashing the chip. The asm text file was written and saved on a Linux box, so there may be issues with the end of line in Windows, although it should be viewable in most browsers.
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Prior to the video switches, there are two preamps for the Luma and the Chroma which condition the signals coming from the VIC-II to an acceptable level, and match up the black level between them. Following the video switches we feed a special video buffer/summing IC chip (FMS6400CS) where the signals get boosted in current capability for a standard 75 ohm load while rendering 1V peak-to-peak video output, and also doing DC signal restoration with some filtering. And finally the Luma and Chroma also get combined inside the FMS6400CS to create an independent fully buffered composite output that will not interfere or cross-talk with the Luma/Chroma outputs.
O-Scope and HD Monitor Images
BASIC Start-Up Screen with VGATE ON (cropping left border over scan)
BASIC Start-Up Screen with VGATE OFF (full left border - no cropping)
Diagnostic Screen VGATE ON (no white line)
Diagnostic Screen VGATE OFF (white line visible)
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