The "rolling bar" results from the Macintosh SE or Macintosh Plus
computer's refresh rate (vertical scan rate) of 60.15 Hz, when
television's refresh (vertical scan) rate is 59.94 Hz.
You can use an external or internal clock at 15.612515 MHz (.35% of the
Macintosh's internal clock) to stabilize the scan line that rolls down the
screen. There are three problems with this:
- Such adjustments void the computer's warranty.
- Ordering a specific oscillator usually takes anywhere from 8 to 12 weeks.
- Once stabilized, the visible scan line will remain visible on the screen.
You might be able to start it within the retrace period (where it rolls
off bottom and begins on the top), but the odds are against it.
After the adjustments discussed above, the Macintosh would not be running
correctly -- at least in a technical sense. The screen refresh rate would
be incorrect, and other Macintosh components dependent on the internal
clock would be slowed down accordingly. There are many possible problems,
but applications would probably continue to function without anyone
noticing any real problems for some time.