diff --git a/src/add-ons/accelerants/nvidia/SetDisplayMode.c b/src/add-ons/accelerants/nvidia/SetDisplayMode.c
index 6e0a984b61..89ff744aeb 100644
--- a/src/add-ons/accelerants/nvidia/SetDisplayMode.c
+++ b/src/add-ons/accelerants/nvidia/SetDisplayMode.c
@@ -184,13 +184,13 @@ status_t SET_DISPLAY_MODE(display_mode *mode_to_set)
 		/*work out where the "right" screen starts*/
 		startadd_right = startadd + (target.timing.h_display * (colour_depth1 >> 3));
 
-		/* fixme: test... */
-		nv_dac_crt_connected();
-		nv_dac2_crt_connected();
-
 		/* set the outputs if possible */
 		if (si->ps.secondary_head)
 		{
+			/* fixme: test... (do also for singlehead modes!) */
+			nv_dac_crt_connected();
+			nv_dac2_crt_connected();
+
 			switch (target.flags & DUALHEAD_BITS)
 			{
 			case DUALHEAD_ON:
diff --git a/src/add-ons/accelerants/nvidia/engine/nv_dac.c b/src/add-ons/accelerants/nvidia/engine/nv_dac.c
index 7417835fbc..11019c6928 100644
--- a/src/add-ons/accelerants/nvidia/engine/nv_dac.c
+++ b/src/add-ons/accelerants/nvidia/engine/nv_dac.c
@@ -23,8 +23,8 @@ bool nv_dac_crt_connected(void)
 	/* save DAC state */
 	dac = DACR(TSTCTRL);
 
-	/* shut-off DAC */
-	DACW(TSTCTRL, (DACR(TSTCTRL) | 0x00010000));
+	/* turn on DAC */
+	DACW(TSTCTRL, (DACR(TSTCTRL) & 0xfffeffff));
 	/* select primary head and turn off CRT (and DVI?) outputs */
 	DACW(OUTPUT, (output & 0x0000feee));
 	/* wait for signal lines to stabilize */
diff --git a/src/add-ons/accelerants/nvidia/engine/nv_dac2.c b/src/add-ons/accelerants/nvidia/engine/nv_dac2.c
index d5038c6301..2a747dcd93 100644
--- a/src/add-ons/accelerants/nvidia/engine/nv_dac2.c
+++ b/src/add-ons/accelerants/nvidia/engine/nv_dac2.c
@@ -21,14 +21,14 @@ bool nv_dac2_crt_connected()
 	/* save DAC state */
 	dac = DAC2R(TSTCTRL);
 
-	/* shut-off DAC */
-	DAC2W(TSTCTRL, (DAC2R(TSTCTRL) | 0x00010000));
+	/* turn on DAC2 */
+	DAC2W(TSTCTRL, (DAC2R(TSTCTRL) & 0xfffeffff));
 	/* select primary head and turn off CRT (and DVI?) outputs */
 	DAC2W(OUTPUT, (output & 0x0000feee));
 	/* wait for signal lines to stabilize */
 	snooze(1000);
 	/* re-enable CRT output */
-	DAC2W(OUTPUT, (DACR(OUTPUT) | 0x00000001));
+	DAC2W(OUTPUT, (DAC2R(OUTPUT) | 0x00000001));
 
 	/* setup RGB test signal levels to approx 30% of DAC range and enable them
 	 * (NOTE: testsignal function block resides in DAC1 only (!)) */