wrote in message
...
On May 27, 8:49 am, "Caius" wrote:
ha scritto nel
...
On May 23, 12:05 am, who where wrote:
That lousy .1uF input to pin 2 cap is much better
when it's 1uF and the 680K resistor on pin 6 works better at 470K.

I tried a 1uf capacitor on pin 2 and nothing has changed (I didn't
obtain
anymore the value of 15.575 KHz on pin 1..).A friend of mine told
me that he
can measure correctly Vsync of 60 Hz with a LM1881 with exactly the
same
circuit on NATIONAL datasheet (the same I'm trying).
So,I can conclude, it's a issue of mine frequency counter...

P.S.
My friend uses a DMM which can measure frequency up to 20 MHz,
probably it
is better (more sensible..) than my "assembled from kit" counter

You cannot make that assumption without a scope which unfortunately
you don't have. I'm only guessing but I bet your video has bad low
frequency tilt which shows of as the 'DC' of the back porch wandering
all over the place. Cause: bad capacitors somewhere in the video
chain. IIRC the Gennum chip includes clamps to guarantee sampling at
50% of the sync pulse meaning it's more tolerant of poor video. The
scope would tell all.

G²

Absolutely agreed on all points

Arfa