diff --git a/src/mame/drivers/backfire.c b/src/mame/drivers/backfire.c
index cdde00263b5..221bbcbccad 100644
--- a/src/mame/drivers/backfire.c
+++ b/src/mame/drivers/backfire.c
@@ -500,14 +500,14 @@ static MACHINE_DRIVER_START( backfire )
 	MDRV_SCREEN_ADD("left", RASTER)
 	MDRV_SCREEN_FORMAT(BITMAP_FORMAT_INDEXED16)
 	MDRV_SCREEN_REFRESH_RATE(60)
-	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(0))
+	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(2500) /* not accurate */)
 	MDRV_SCREEN_SIZE(40*8, 32*8)
 	MDRV_SCREEN_VISIBLE_AREA(0*8, 40*8-1, 1*8, 31*8-1)
 
 	MDRV_SCREEN_ADD("right", RASTER)
 	MDRV_SCREEN_FORMAT(BITMAP_FORMAT_INDEXED16)
 	MDRV_SCREEN_REFRESH_RATE(60)
-	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(0))
+	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(2500) /* not accurate */)
 	MDRV_SCREEN_SIZE(40*8, 32*8)
 	MDRV_SCREEN_VISIBLE_AREA(0*8, 40*8-1, 1*8, 31*8-1)
 
diff --git a/src/mame/drivers/m107.c b/src/mame/drivers/m107.c
index 7c4feb22199..4076d046344 100644
--- a/src/mame/drivers/m107.c
+++ b/src/mame/drivers/m107.c
@@ -495,7 +495,7 @@ static MACHINE_DRIVER_START( firebarr )
 	/* video hardware */
 	MDRV_SCREEN_ADD("main", RASTER)
 	MDRV_SCREEN_REFRESH_RATE(60)
-	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(0))
+	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(2500) /* not accurate */)
 	MDRV_SCREEN_FORMAT(BITMAP_FORMAT_INDEXED16)
 	MDRV_SCREEN_SIZE(512, 256)
 	MDRV_SCREEN_VISIBLE_AREA(80, 511-112, 8, 247) /* 320 x 240 */
diff --git a/src/mame/drivers/naomi.c b/src/mame/drivers/naomi.c
index 075341e416e..59d33ffa585 100644
--- a/src/mame/drivers/naomi.c
+++ b/src/mame/drivers/naomi.c
@@ -788,7 +788,7 @@ static MACHINE_DRIVER_START( naomi )
 	/* video hardware */
 	MDRV_SCREEN_ADD("main", RASTER)
 	MDRV_SCREEN_REFRESH_RATE(60)
-	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(0))
+	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(2500) /* not accurate */)
 	MDRV_SCREEN_FORMAT(BITMAP_FORMAT_RGB32)
 	MDRV_SCREEN_SIZE(640, 480)
 	MDRV_SCREEN_VISIBLE_AREA(0, 640-1, 0, 480-1)
diff --git a/src/mame/drivers/sidearms.c b/src/mame/drivers/sidearms.c
index 75edb097085..8638cbbb6b7 100644
--- a/src/mame/drivers/sidearms.c
+++ b/src/mame/drivers/sidearms.c
@@ -729,7 +729,7 @@ static MACHINE_DRIVER_START( sidearms )
 
 	MDRV_SCREEN_ADD("main", RASTER)
 	MDRV_SCREEN_REFRESH_RATE(60)
-	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(0))
+	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(2500) /* not accurate */)
 	MDRV_SCREEN_FORMAT(BITMAP_FORMAT_INDEXED16)
 	MDRV_SCREEN_SIZE(64*8, 32*8)
 	MDRV_SCREEN_VISIBLE_AREA(8*8, (64-8)*8-1, 2*8, 30*8-1 )
@@ -775,7 +775,7 @@ static MACHINE_DRIVER_START( turtship )
 
 	MDRV_SCREEN_ADD("main", RASTER)
 	MDRV_SCREEN_REFRESH_RATE(60)
-	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(0))
+	MDRV_SCREEN_VBLANK_TIME(ATTOSECONDS_IN_USEC(2500) /* not accurate */)
 	MDRV_SCREEN_FORMAT(BITMAP_FORMAT_INDEXED16)
 	MDRV_SCREEN_SIZE(64*8, 32*8)
 	MDRV_SCREEN_VISIBLE_AREA(8*8, (64-8)*8-1, 2*8, 30*8-1 )
diff --git a/src/mame/video/astrocde.c b/src/mame/video/astrocde.c
index bad3cd93ef5..348ff733b5d 100644
--- a/src/mame/video/astrocde.c
+++ b/src/mame/video/astrocde.c
@@ -468,7 +468,8 @@ static TIMER_CALLBACK( scanline_callback )
 	int astrocade_scanline = mame_vpos_to_astrocade_vpos(scanline);
 
 	/* force an update against the current scanline */
-	video_screen_update_partial(machine->primary_screen, scanline - 1);
+	if (scanline > 0)
+		video_screen_update_partial(machine->primary_screen, scanline - 1);
 
 	/* generate a scanline interrupt if it's time */
 	if (astrocade_scanline == interrupt_scanline && (interrupt_enable & 0x08) != 0)
diff --git a/src/mame/video/leland.c b/src/mame/video/leland.c
index bc2e432b51e..c55ee859465 100644
--- a/src/mame/video/leland.c
+++ b/src/mame/video/leland.c
@@ -82,26 +82,26 @@ static VIDEO_START( ataxx )
 
 WRITE8_HANDLER( leland_scroll_w )
 {
+	int scanline = video_screen_get_vpos(machine->primary_screen);
+	if (scanline > 0)
+		video_screen_update_partial(machine->primary_screen, scanline - 1);
+
 	/* adjust the proper scroll value */
 	switch (offset)
 	{
 		case 0:
-			video_screen_update_partial(machine->primary_screen, video_screen_get_vpos(machine->primary_screen) - 1);
 			xscroll = (xscroll & 0xff00) | (data & 0x00ff);
 			break;
 
 		case 1:
-			video_screen_update_partial(machine->primary_screen, video_screen_get_vpos(machine->primary_screen) - 1);
 			xscroll = (xscroll & 0x00ff) | ((data << 8) & 0xff00);
 			break;
 
 		case 2:
-			video_screen_update_partial(machine->primary_screen, video_screen_get_vpos(machine->primary_screen) - 1);
 			yscroll = (yscroll & 0xff00) | (data & 0x00ff);
 			break;
 
 		case 3:
-			video_screen_update_partial(machine->primary_screen, video_screen_get_vpos(machine->primary_screen) - 1);
 			yscroll = (yscroll & 0x00ff) | ((data << 8) & 0xff00);
 			break;
 
@@ -200,7 +200,9 @@ static void leland_vram_port_w(int offset, int data, int num)
 
 	/* don't fully understand why this is needed.  Isn't the
        video RAM just one big RAM? */
-	video_screen_update_partial(Machine->primary_screen, video_screen_get_vpos(Machine->primary_screen) - 1);
+	int scanline = video_screen_get_vpos(Machine->primary_screen);
+	if (scanline > 0)
+		video_screen_update_partial(Machine->primary_screen, scanline - 1);
 
 	if (LOG_COMM && addr >= 0xf000)
 		logerror("%04X:%s comm write %04X = %02X\n", activecpu_get_previouspc(), num ? "slave" : "master", addr, data);