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From: Arfa Daily on 28 May 2010 21:13

<stratus46(a)yahoo.com> wrote in message
news:2e43c598-7127-469b-8e55-264cf7d6285d(a)o12g2000vba.googlegroups.com...
On May 27, 8:49 am, "Caius" <bric...(a)yahoo.it> wrote:
> <stratu...(a)yahoo.com> ha scritto nel
> messaggionews:2709ccd5-9830-49f7-a95d-78179fc1eb3e(a)v37g2000vbv.googlegroups.com...
> On May 23, 12:05 am, who where <no...(a)home.net> 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.

G�

Absolutely agreed on all points

Arfa


From: Caius on 29 May 2010 09:15

<stratus46(a)yahoo.com> ha scritto nel messaggio
news:2e43c598-7127-469b-8e55-264cf7d6285d(a)o12g2000vba.googlegroups.com...
On May 27, 8:49 am,
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.

G�

Ok, thanks.Sadly the video (R,G,B ground + SYNC) is from arcade videogame
pcb, so I assume they have all poor video signal???
I 'd wan to try the Gennum GS4981 but it seems unfindable...


From: who where on 29 May 2010 20:52
On Sat, 29 May 2010 15:15:36 +0200, "Caius" <briccus(a)yahoo.it> wrote:

>
><stratus46(a)yahoo.com> ha scritto nel messaggio
>news:2e43c598-7127-469b-8e55-264cf7d6285d(a)o12g2000vba.googlegroups.com...
>On May 27, 8:49 am,
>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.
>
>G�
>
>Ok, thanks.Sadly the video (R,G,B ground + SYNC) is from arcade videogame
>pcb, so I assume they have all poor video signal???
>I 'd wan to try the Gennum GS4981 but it seems unfindable...

?? have you tried their website? Google "gennum gs4981" and first
hit. Then go to the "buy from distributor" or "get free sample"
(sounds better) link at
http://www.gennum.com/buy/sales-network
From: Caius on 30 May 2010 08:18

"who where" <noone(a)home.net> ha scritto nel messaggio
news:phd306haattb3443pgl0atfka2difj2ch2(a)4ax.com...
> ?? have you tried their website? Google "gennum gs4981" and first
> hit. Then go to the "buy from distributor" or "get free sample"
> (sounds better) link at
> http://www.gennum.com/buy/sales-network

Ok, thanks.I will try with the GS4981 instead of LM1881.
But, are you sure I will solve my problem with this IC?


From: who where on 30 May 2010 20:35
On Sun, 30 May 2010 14:18:35 +0200, "Caius" <briccus(a)yahoo.it> wrote:

>
>"who where" <noone(a)home.net> ha scritto nel messaggio
>news:phd306haattb3443pgl0atfka2difj2ch2(a)4ax.com...
> > ?? have you tried their website? Google "gennum gs4981" and first
>> hit. Then go to the "buy from distributor" or "get free sample"
>> (sounds better) link at
>> http://www.gennum.com/buy/sales-network
>
>Ok, thanks.I will try with the GS4981 instead of LM1881.
>But, are you sure I will solve my problem with this IC?

Not at all. But (a) it did for us, and (b) it won't cost a fortune to
try - especially if you can get a "sample".

Be aware though that although the DS1881 is a drop-in replacment for
the LM1881, the GS4981 has a different pinout.
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