Hi all,
I found in this page:
http://geocities.ws/podernixie/htpc/...tml#jammascart (http://geocities.ws/podernixie/htpc/...tml#jammascart)
that a 1KOhm resistor is needed on the Sync PIN.Now, in my selfmade Supergun I don't have this resistor while I have the three 220Ohm resistors on RBG and I get perfect colours on my SCART TV and also sync is good except for some PCBs (bootlegs mainly) that roll up and down.For example I have a Pitfall II PCB which syncs well in a Sony TV while it rolls in a Grundig TV and in a Amiga monitor M1438s which is connected to the Supergun through a sync splitter (with EL4583 IC) since this monitor accepts only H and V sync.
So my question is:
Is that 1KOhm resistor really necessary on the Sync pin?What is its utility?
Thanks..
P.S.
Is it possibile to add some circuit to adjust vertical sync on a JAMMA Supergun?I know on arcade monitor it's possibile.
I've never had a resistor on sync on my superguns and they all synced fine.
Some TVs (sometimes the older ones) don't like too much voltage on the sync. I had trouble with a couple of old Philips sets. One would roll when ever the screen went bright white and the other would actually trip its protection circuitry. A resistor on the composite line (used for sync on RGB scart) seemed to fix the problem. I cant see it doing any damage if you try
It's very common for arcade boards to overdrive the connections. In fact, the majority of my PCBs put out too much power on the RGB and S lines, typically 1V instead of the standard 0.7V. This resistor will certainly drop the voltage, probably too much, but a TV is much better at using low-V syncs than high-V.