To install the VIC-II2, you remove the original crystal from the motherboard and install a pin header in its place. This gets routed through the PAL or NTSC frequency crystals on the VIC-II2 depending on which mode you have selected. The rest of the timing circuit on the mainboard is still in use, including the discrete 74-series, the 15pf or 16pf tuning capacitor, and the adjustable trimming capacitor. The difficulty is just that you must lift the board to access the trimmer. The VIC-II2 isn't capable of dividing the clock, it doesn't have any components for timing other than these two crystals. It leaves everything to the motherboard's clock circuit.eslapion wrote: ↑Sat Feb 01, 2020 4:18 pmYou're saying total nonsense here. When you use the VIC-II2, the C64's capacitor and crystal is UNUSED. This board doesn't know what type of C64 board it's going to be installed on so it carries both frequencies since you have both types of 656X. They are clearly marked 'NTSC crystal' and 'PAL Crystal'.
On PAL systems, the dot clock is 4/9 of the color clock and on NTSC systems, the dot clock is 4/7 of the color clock. The VIC-II2 board takes care of the conversion depending on the system/video chip you selected.
The VIC-II2 has it's own 14.31818MHz crystal and it's own 17.7344 MHz crystal. You could completely cut off the crystal that's on the C64 board and everything would still work.
There is a different version of the PCB for use with 250425, because of different mainboard layout, but it similarly just replaces the crystal itself.
I checked that, and I also checked the dot clock frequency on an adjacent pin. I did get it extremely close, certainly within the accuracy of turning a tuning capacitor. I will take another look and get a picture. Oh yes, I have heat sinks bonded to both VIC-IIs with thermal silicone, these can be seen in my first picture. They were just bare for brief testing before I buttoned everything up.
Ah! Then I may give it a test soon.
Pardon the misunderstanding. I think it was not initially obvious the VIC-II2 doesn't replace any timing components other than the crystal, and I read that with the idea that you knew this.eslapion wrote: ↑Sat Feb 01, 2020 4:18 pmI NEVER said anything like that!!rmzalbar wrote: I think eslapion has hit it on the head however with a mismatch in phase between dot and color clock. Now to determine what to do next.
If the color clock is wrong, everything else is derived from it* so everything else will be wrong too. It only needs an error of less than 0.1% for the colors to go wrong. Correctly tuned crystal usually have an error of about 50ppm or less, that's 0.0003%.
* On PAL C64, that's phiColor=17.7344 MHz, phiDot=(4/9) x phiColor=7.882MHz, phi0=(1/8) x phiDot=0.98525MHz
I discovered in tuning that the NTSC color was initially sea-green and the PAL color wasn't being detected at all (black and white) due to the new capacitance involved in the crystal switching circuit. Once I put the scope on it and made adjustments, the NTSC color became correct and I got color video in PAL. However, no amount of tuning seemed to reduce these bars. I'll give it another look.