Anyone have a circuit to alter v-sync pulse?

[XianXi]

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.

[viletim]

You could do it with one-shots, R/C delays. Here's how to do it with a 558 (quad 555).

Code Select Expand

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

[XianXi]

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?

[XianXi]

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