Monitor refresh rate query

Peter Corlett abuse at
Fri Jun 17 13:49:15 CDT 2016

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.

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