Changing the scan rate of the analog board seems unlikely to work, and definitely won't get anywhere near 68kHz, so I thought it would be worth trying something different:
Approach
The way I'm working on this now is to run the yoke and the flyback and two completely separate circuits. In other words: disconnect the horizontal coil from the analog board, and then build a new circuit on similar principles to drive it. Hopefully, this means the flyback can continue to run at its usual 22.25kHz frequency to generate all the CRT voltages, while the yoke can do something completely different at whatever frequency we want.
Presumably the vertical sweep circuit on the analog board can still be used, maybe with small modifications. I haven't gotten that far yet.
Some goals
This approach will involve building a second circuit just to run the yoke. Ideally, I'd like to do this without requiring another Mac for donor parts. That means all the custom Apple components (yoke, inductors, transformers) should be needed in either the flyback or the yoke circuit, but not both.
I'm not quite there yet, but I think it will be possible.
Other measurements
I measured a few components on my Plus to get an idea of what's needed. The BOMARC schematics and Thomas Lee's Classic Mac Repair Notes also have some useful measurements.
Yoke resistance/inductance: vertical coil = 8.3 ohms; horizontal coil = 0.1 ohms. Horizontal coil appears to be about 80uH.
L2 (width coil): in its default setting, measured 23uH. I didn't measure the whole range but someone has done that on another thread (don't remember where).
L3 (linearity coil / saturating inductor): it was hard to get a clear measurement on this, but I think it may be around 12uH. It may be less.
The capacitors measured reasonably close to their rated values. C4 on the Plus is .027uF. The equivalent on the SE is .033uF.
Approach
The way I'm working on this now is to run the yoke and the flyback and two completely separate circuits. In other words: disconnect the horizontal coil from the analog board, and then build a new circuit on similar principles to drive it. Hopefully, this means the flyback can continue to run at its usual 22.25kHz frequency to generate all the CRT voltages, while the yoke can do something completely different at whatever frequency we want.
Presumably the vertical sweep circuit on the analog board can still be used, maybe with small modifications. I haven't gotten that far yet.
Some goals
This approach will involve building a second circuit just to run the yoke. Ideally, I'd like to do this without requiring another Mac for donor parts. That means all the custom Apple components (yoke, inductors, transformers) should be needed in either the flyback or the yoke circuit, but not both.
I'm not quite there yet, but I think it will be possible.
Other measurements
I measured a few components on my Plus to get an idea of what's needed. The BOMARC schematics and Thomas Lee's Classic Mac Repair Notes also have some useful measurements.
Yoke resistance/inductance: vertical coil = 8.3 ohms; horizontal coil = 0.1 ohms. Horizontal coil appears to be about 80uH.
L2 (width coil): in its default setting, measured 23uH. I didn't measure the whole range but someone has done that on another thread (don't remember where).
L3 (linearity coil / saturating inductor): it was hard to get a clear measurement on this, but I think it may be around 12uH. It may be less.
The capacitors measured reasonably close to their rated values. C4 on the Plus is .027uF. The equivalent on the SE is .033uF.