17 Jun
2016
17 Jun
'16
11:49 a.m.
On Fri, Jun 17, 2016 at 11:36:14AM -0400, Noel Chiappa wrote:
[...]
(Parenthetically, what exactly is the mechanism that
causes damage if you run
an old CRT monitor at too high a refresh rate? I assume the excessive speed
generates too much heat somewhere, and causes transistors to fail, or
something like that?)
To generate high voltage DC such as that necessary to emit an electron beam,
one typically feeds an AC signal into a voltage multiplier circuit. Textbooks
will show some nice clean circuits which multiply by a fixed integer, but
real-world components don't read textbooks and the output voltage also varies
by frequency.
If one is building a fixed-frequency display (e.g. a TV), one can cut corners
and save a few bob by recycling the line output frequency (~15kHz for both PAL
and NTSC) to generate this AC. So if the line output frequency goes up, so can
the beam voltage, possibly to dangerous levels.
[...]
So is there some bizarre interlace mode, or something,
that could
legitimately cause confusion over the vertical retrace? Or is the second
monitor just confused?
Both are correct. There are 44 (rounded) frames per second, and 87 (rounded)
fields per second.