diff --git a/asm_routines/mockingboard.s b/asm_routines/mockingboard.s
index 07b8e78a..d592ec4c 100644
--- a/asm_routines/mockingboard.s
+++ b/asm_routines/mockingboard.s
@@ -158,45 +158,79 @@ clear_ay_right_loop:
 	; Attempts to time an instruction sequence with a 6522
 	;
 	; If found, puts in  bMB
-	; OUT2: has address of Mockingboard
-
-bMB	EQU	$03
-OUT2	EQU	$22	; +$21
-bGood	EQU	$FE	; 0 : ok / 1 : bad
-Temp	EQU	$FF	;
-
+	; MB_ADDRL:MB_ADDRH has address of Mockingboard
+	; returns X=0 if not found, X=1 if found
 
 mockingboard_detect:
 	lda	#0
-	sta	OUT2
+	sta	MB_ADDRL
 
 mb_detect_loop:	; self-modifying
 	lda	#$07	; we start in slot 7 ($C7) and go down to 0 ($C0)
 	ora	#$C0	; make it start with C
-	sta	OUT2+1
+	sta	MB_ADDRH
 	ldy	#04	; $CX04
 	ldx	#02	; 2 tries?
 mb_check_cycle_loop:
-	lda	(OUT2),Y		; timer 6522 (Low Order Counter)
+	lda	(MB_ADDRL),Y		; timer 6522 (Low Order Counter)
 					; count down
-	sta	Temp			; 3 cycles
-	lda	(OUT2),Y		; + 5 cycles = 8 cycles
+	sta	TEMP			; 3 cycles
+	lda	(MB_ADDRL),Y		; + 5 cycles = 8 cycles
 					; between the two accesses to the timer
 	sec
-	sbc	Temp			; subtract to see if we had 8 cycles
+	sbc	TEMP			; subtract to see if we had 8 cycles
 	cmp	#$f8			; -8
 	bne	mb_not_in_this_slot
 	dex				; decrement, try one more time
 	bne	mb_check_cycle_loop	; loop detection
 	inx				; Mockingboard found (X=1)
 done_mb_detect:
-	stx	bMB			; store result to bMB
+	;stx	bMB			; store result to bMB
 	rts				; return
 
 mb_not_in_this_slot:
 	dec	mb_detect_loop+1	; decrement the "slot" (self_modify)
 	bne	mb_detect_loop		; loop down to one
-	inc	bGood			; didn't find?
 	ldx	#00
 	beq	done_mb_detect
 
+
+	;=======================================
+	; Detect a Mockingboard card in Slot4
+	;=======================================
+	; Based on code from the French Touch "Pure Noise" Demo
+	; Attempts to time an instruction sequence with a 6522
+	;
+	; MB_ADDRL:MB_ADDRH has address of Mockingboard
+	; returns X=0 if not found, X=1 if found
+
+mockingboard_detect_slot4:
+	lda	#0
+	sta	MB_ADDRL
+
+mb4_detect_loop:	; self-modifying
+	lda	#$04	; we're only looking in Slot 4
+	ora	#$C0	; make it start with C
+	sta	MB_ADDRH
+	ldy	#04	; $CX04
+	ldx	#02	; 2 tries?
+mb4_check_cycle_loop:
+	lda	(MB_ADDRL),Y		; timer 6522 (Low Order Counter)
+					; count down
+	sta	TEMP			; 3 cycles
+	lda	(MB_ADDRL),Y		; + 5 cycles = 8 cycles
+					; between the two accesses to the timer
+	sec
+	sbc	TEMP			; subtract to see if we had 8 cycles
+	cmp	#$f8			; -8
+	bne	mb4_not_in_this_slot
+	dex				; decrement, try one more time
+	bne	mb4_check_cycle_loop	; loop detection
+	inx				; Mockingboard found (X=1)
+done_mb4_detect:
+	rts				; return
+
+mb4_not_in_this_slot:
+	ldx	#00
+	beq	done_mb4_detect
+