These damn Midway boards are driving me nuts. The picture is shifted about 20-25px down the screen, only got this problem with Midway boards.
Any help would be greatly appreciated.
You could do it with one-shots, R/C delays. Here's how to do it with a 558 (quad 555).
V-sync 60Hz, 16.67mS
----+ +--------------------------------+ +------
| | <- 16.51mS -> | |
+-+ +-+
^0.16mS
First one-shot 10mS
+-----------------+
| |
----+ +-------------------------
Second one-shot 5.39mS (first + second - 20 lines)
+---------------+
| |
----------------------+ +---------
Third one-shot 0.16mS
+-+
| |
--------------------------------------+ +-------
Third one-shot (inverted)
--------------------------------------+ +-------
| |
+-+
- The reason for the intermediary 10mS pulse is that most one-shots have problems generating pulses at > 80% duty cycle.
- I have no idea how long a typical arcade board vertical sync pulse is, 0.16mS is from PAL TV
Is there a way to build one with a pot so it's adjustable on the fly? Could I just use a pot on the cset pin to ground to do this?
Hmmm, I am also getting some problems with 2 other boards as the vsync is way off. Is this not possible at all with a pot, how does the vhold work on a TV that has the pots? I'm guessing it is like a monitor chassis board just like in an arcade cab or something.
I was searching around and found an IC that looks like it can do what I need, TDA-1175P. Looking at the data sheet it looks like a simple straight forward circuit, but will it work. Anyone know for sure?
On one of the Tennis games I have it has the last 20px of the picture at the very top of the screen.
http://www.datasheetcatalog.com/datasheets_pdf/T/D/A/1/TDA1175P.shtml