diff --git a/Source/HBIOS/sn76489.asm b/Source/HBIOS/sn76489.asm
index 866b7c50..812ea274 100644
--- a/Source/HBIOS/sn76489.asm
+++ b/Source/HBIOS/sn76489.asm
@@ -93,7 +93,7 @@ SN7_VOLUME_OFF:
 
 #IFDEF SBCV2004
 	LD	A,(HB_RTCVAL)
-	OR	%11110111		; SBC-V2-004+ CHANGE TO
+	AND	%11110111		; SBC-V2-004+ CHANGE TO
 	OUT	(RTCIO),A		; NORMAL CLOCK SPEED
 #ENDIF