HELP:Measuring refresh rate of PCBs

[Caiusfabricius]

Hi all,
I built a simple circuit using te famous "sync separator" IC LM1881 in order
to measure the refresh rate (Vsync) of JAMMA PCBs.I follow this scheme (but
also the one form NATIONAL manufacturer is fine):

http://www.gamoover.net/tuto/schema-de-montage-du-lm1881-s%C3%A9paration-de-la-synchro-du-signal-composite

The problem is that when I try to measure with a frequency counter the
vertical sync output on PIN 3 of the LM1818 I obtain bad values (in order of
Khz not in Hz as it should be.Usually it should be about 60Hz)
To say that I check the circuit and is OK as well as my frequency counter
that works fine when I measure, for example, the clock of the various CPU.

Any suggestions?I'm going crazy...

P.S.
I use the VIDEO Sync (pin P of solder side of the jamma connector) as
COMPOSITE VIDEO IN (pin 2 of the LM1881)

 

[Dave M]

Caiusfabricius wrote:

Hi all,
I built a simple circuit using te famous "sync separator" IC LM1881
in order to measure the refresh rate (Vsync) of JAMMA PCBs.I follow
this scheme (but also the one form NATIONAL manufacturer is fine):

http://www.gamoover.net/tuto/schema-de-montage-du-lm1881-s%C3%A9paration-de-la-synchro-du-signal-composite

The problem is that when I try to measure with a frequency counter the
vertical sync output on PIN 3 of the LM1818 I obtain bad values (in
order of Khz not in Hz as it should be.Usually it should be about
60Hz) To say that I check the circuit and is OK as well as my frequency
counter that works fine when I measure, for example, the clock of the
various CPU.
Any suggestions?I'm going crazy...

P.S.
I use the VIDEO Sync (pin P of solder side of the jamma connector) as
COMPOSITE VIDEO IN (pin 2 of the LM1881)

What kind of counter are you using? What are its trigger voltage levels
(adjustable or fixed)? Have you monitored the input and output signals with
a scope while you have the counter connected? What do the signals look like
(voltage levels, noise, etc.)? Have you adeqquately decoupled the LM1818
power supply pins?
--
David
dgminala at mediacombb dot net

 

[Caius]

"Dave M" <dgminala4444@mediacombb.net> ha scritto nel messaggio
news:q8GdndOC6PEx_2XWnZ2dnUVZ_gOdnZ2d@giganews.com...

What kind of counter are you using? What are its trigger voltage levels
(adjustable or fixed)?

I use this counter:

http://cgi.ebay.it/0Hz-to-50Mhz-Frequency-Counter-Module-Kit-LCD-display-/140353600315?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item20adb9fb3b#ht_1974wt_939

Have you monitored the input and output signals with a scope while you have
the counter connected? What do the signals look like (voltage levels,
noise, etc.)?

I don't have a scope

Have you adeqquately decoupled the LM1818

power supply pins?

What did you mean for 'dcoupled'?Adding capacitors?
No, ground and power pins are directly connected to the ground and +5 Volt
of my JAMMA test rig.

--

David
dgminala at mediacombb dot net