to fix the problem - do the following

 cd /sys/arch/pmax
 patch -p0 < fb.patch

rebuild and install a new kernel

Index: dev/qvss_compat.c
===================================================================
RCS file: /cvs/src/sys/arch/pmax/dev/qvss_compat.c,v
retrieving revision 1.4
retrieving revision 1.6
diff -u -r1.4 -r1.6
--- qvss_compat.c       1997/06/10 14:18:48     1.4
+++ qvss_compat.c       1998/01/28 11:38:28     1.6
@@ -563,12 +563,12 @@
               break;
#endif /* NDC_DS */

-#if NSCC > 1
+#if NSCC > 0
       case DS_3MIN:
       case DS_3MAXPLUS:
-               sccDivertXInput = genKbdEvent;
-               sccMouseEvent = genMouseEvent;
-               sccMouseButtons = genMouseButtons;
+               sccDivertXInput = (void (*) __P((int)))genKbdEvent;
+               sccMouseEvent = (void (*) __P((int)))genMouseEvent;
+               sccMouseButtons = (void (*) __P((int)))genMouseButtons;
               break;
#endif
#if NDTOP > 0
@@ -611,12 +611,12 @@
               break;
#endif /* NDC_DS */

-#if NSCC > 1
+#if NSCC > 0
       case DS_3MIN:
       case DS_3MAXPLUS:
-               sccDivertXInput = (void (*) __P((int)) )0;
-               sccMouseEvent = (void (*) __P((MouseReport *)) )0;
-               sccMouseButtons = (void (*) __P((MouseReport *)) )0;
+               sccDivertXInput = (void (*) __P((int)))0;
+               sccMouseEvent = (void (*) __P((int)))0;
+               sccMouseButtons = (void (*) __P((int)))0;
               break;
#endif