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):
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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)