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F2 Help!

GF77

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May 8, 2025
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Got a Metal Black whiche behaves a lttle strange on the sync side. It's the long board version if that matters.

For some reason I have an unstable horizontal sync on my (SCART) 1084 non-S. On the upper half of the display some lines are shaky. Now if I shift the picture horizontally everything will shift except that upper portion of the screen. Put the PCB into a Blast City, no problem. Every other PCB I own doesn't have any sync issues with this monitor. Maybe putting in the missing 1K resistor on sync will help? But I doubt. Or is my monitor getting a bit rusty catching such uncommon sync behavior? Any thoughts on that?
 
Could be worth trying:

 
I also noticed that the 4 big caps on each corner of the ROM/ext. board are missing/ripped off. Hm, maybe that missing filtering could cause such unstable behavior on my particular monitor? Gotta replace them asap.
 
Caps have always helped stabilize sync on any board I've recapped thus far.
Arcade boards get thrashed on location, I've seen big improvements on f3, I need to do my f2 boards still.
 
Thanks, sounds promising. All four caps are connected to the general ground plane (parts side). And on the other side to another plane. Just have to find out the specs of these caps specifically for the Metal Black ROM/extra GPU board with the TC0480 chip.
 
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