68kMLA Classic Interface

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technical question on the VGA Color Classic mod
Posted by: mraroid on 2015-05-25 08:35:52 Hi folks... I have a technical question (?) on Chris Lawson's VGA mod of the Color Classic.: http://colourclassicfaq.com/general/vga.html First, I would like to quote a post made by member APM on this forum. His post got my gears turning (thank you APM). I hope it is OK to cross post this APM.... APM said: "I don't own a CC and haven't done this modification, but I've looked at the horizontal sweep circuits of the B&W compacts in some detail. I think the CRT shouldn't be your concern here. The reason for the higher sweep voltage is to drive the horizontal deflection coil to move the beam faster across the screen. More voltage across the coil = faster change in deflection current over time = higher possible horizontal frequency. The CRT itself doesn't see any of this, and it doesn't care about the screen resolution per se (which is a function of the yoke). The CRT only sees the HV from the flyback plus the various other voltages at the neck. I'd expect that those voltages will remain the same with this mod, since the picture quality remains similar. In other words, done correctly, there's no reason to think you'd shorten the life of the CRT, though it may be added load on the flyback transformer or other parts of the analog board. But I would guess those components are easier to replace if it ever came up. I'm sure someone who has done the modification before can comment on whether it has any issues with the analog board deteriorating over time". *********************** Here is my question: Can anyone run some numbers by me? What H and V frequencies are used in the stock CC machine, and what are they after the mod? I am not to worried about the extra sweep voltage, but frequency (pitch) changes can cause problems for the unwary. Essentially, the horizontal sweep / high voltage system in a tv is a switch mode power supply . So when in doubt (like I said, I am geting chicken about doing this mod), I'd do minor or no changes at all.
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