italie |
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MAME owes italie many thank yous, hah
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Reged: 09/20/03
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Posts: 15246
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Loc: BoomTown
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Re: HELP:Measuring refresh rate of PCBs
01/04/11 04:22 AM
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> Hi all,
> I built a simple circuit using the 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-m...ignal-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)
Sounds like Hsync values.... What PCB are you testing? Do these results show up on multiple PCBs?
What does pin 7 on the LM1881N read?
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