diff --git a/src/com/bytezone/diskbrowser/applefile/HiResImage.java b/src/com/bytezone/diskbrowser/applefile/HiResImage.java
index c719345..a61879f 100644
--- a/src/com/bytezone/diskbrowser/applefile/HiResImage.java
+++ b/src/com/bytezone/diskbrowser/applefile/HiResImage.java
@@ -29,7 +29,7 @@ public abstract class HiResImage extends AbstractFile
   //   $08 FOT  <$4000  Apple II Graphics File       -       ???
   //   $08 FOT   $4000  Packed Hi-Res file           -       ???
   //   $08 FOT   $4001  Packed Double Hi-Res file    -       ???
-  //   $08 FOT   $8066  Fadden Hi-res
+  //   $08 FOT   $8066  Fadden Hi-res                - FaddenHiResImage
 
   // * $C0 PNT   $0000  Paintworks Packed Super Hi-Res           - SHRPictureFile2 
   // * $C0 PNT   $0001  Packed IIGS Super Hi-Res Image           - SHRPictureFile2 
@@ -488,6 +488,8 @@ public abstract class HiResImage extends AbstractFile
 
   public static boolean isAPP (byte[] buffer)
   {
+    if (buffer.length < 4)
+      return false;
     return buffer[0] == (byte) 0xC1 && buffer[1] == (byte) 0xD0
         && buffer[2] == (byte) 0xD0 && buffer[3] == 0;
   }
diff --git a/src/com/bytezone/diskbrowser/disk/DataDisk.java b/src/com/bytezone/diskbrowser/disk/DataDisk.java
index 9ff9b44..6394195 100755
--- a/src/com/bytezone/diskbrowser/disk/DataDisk.java
+++ b/src/com/bytezone/diskbrowser/disk/DataDisk.java
@@ -1,5 +1,6 @@
 package com.bytezone.diskbrowser.disk;
 
+import java.util.ArrayList;
 import java.util.List;
 
 import com.bytezone.diskbrowser.gui.DataSource;
@@ -35,7 +36,7 @@ public class DataDisk extends AbstractFormattedDisk
   @Override
   public List<DiskAddress> getFileSectors (int fileNo)
   {
-    return null;
+    return new ArrayList<> ();
   }
 
   // no files on data disks
diff --git a/src/com/bytezone/diskbrowser/disk/UnknownDisk.java b/src/com/bytezone/diskbrowser/disk/UnknownDisk.java
new file mode 100644
index 0000000..25d12bd
--- /dev/null
+++ b/src/com/bytezone/diskbrowser/disk/UnknownDisk.java
@@ -0,0 +1,20 @@
+package com.bytezone.diskbrowser.disk;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class UnknownDisk extends AbstractFormattedDisk
+{
+  // could arrange for the blocks to appear as a question mark
+
+  public UnknownDisk (AppleDisk disk)
+  {
+    super (disk);
+  }
+
+  @Override
+  public List<DiskAddress> getFileSectors (int fileNo)
+  {
+    return new ArrayList<> ();
+  }
+}
diff --git a/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java b/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java
index 67a4684..d2928dc 100644
--- a/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java
+++ b/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java
@@ -231,6 +231,7 @@ abstract class AbstractCatalogEntry implements AppleFileSource
             byte[] buf = new byte[exactBuffer.length - 4];
             System.arraycopy (exactBuffer, 4, buf, 0, buf.length);
             appleFile = new BasicProgram (name, buf);
+            System.out.printf ("Possible basic binary: %s%n", name);
           }
           else
           {
diff --git a/src/com/bytezone/diskbrowser/nib/DiskAddressField.java b/src/com/bytezone/diskbrowser/nib/DiskAddressField.java
index 4d14d65..1dd2c8d 100644
--- a/src/com/bytezone/diskbrowser/nib/DiskAddressField.java
+++ b/src/com/bytezone/diskbrowser/nib/DiskAddressField.java
@@ -14,6 +14,10 @@ class DiskAddressField
     track = decode4and4 (buffer, 2);
     sector = decode4and4 (buffer, 4);
     checksum = decode4and4 (buffer, 6);
+
+    //    if (track == 0)
+    //      for (int i = 0; i < 8; i++)
+    //        System.out.printf ("%02X ", buffer[i]);
   }
 
   // ---------------------------------------------------------------------------------//
diff --git a/src/com/bytezone/diskbrowser/nib/MC3470.java b/src/com/bytezone/diskbrowser/nib/MC3470.java
index 8920f3c..539b826 100644
--- a/src/com/bytezone/diskbrowser/nib/MC3470.java
+++ b/src/com/bytezone/diskbrowser/nib/MC3470.java
@@ -3,8 +3,6 @@ package com.bytezone.diskbrowser.nib;
 import java.util.ArrayList;
 import java.util.List;
 
-import com.bytezone.diskbrowser.disk.*;
-
 class MC3470
 {
   private static final int MAX_DATA = 999;
@@ -148,6 +146,9 @@ class MC3470
     if (dataPtr < 3)            // not enough bytes to test
       return;
 
+    //    System.out.printf ("checking %02X %02X %02X%n", dataBuffer[dataPtr - 3],
+    //        dataBuffer[dataPtr - 2], dataBuffer[dataPtr - 1]);
+
     if (match (address16prologue) || match (address16prologueX))
     {
       diskReader = diskReader16Sector;
diff --git a/src/com/bytezone/diskbrowser/prodos/FileEntry.java b/src/com/bytezone/diskbrowser/prodos/FileEntry.java
index 01fdd22..102568c 100755
--- a/src/com/bytezone/diskbrowser/prodos/FileEntry.java
+++ b/src/com/bytezone/diskbrowser/prodos/FileEntry.java
@@ -356,10 +356,12 @@ class FileEntry extends CatalogEntry implements ProdosConstants
 
         case FILE_TYPE_FOT:
           if (auxType == 0x8066)        // Fadden
-            //            file = new DefaultAppleFile (name, exactBuffer);
             file = new FaddenHiResImage (name, exactBuffer, fileType, auxType, endOfFile);
           else
+          {
+            System.out.println ("Unwritten FOT: " + name);
             file = new DefaultAppleFile (name, exactBuffer);
+          }
           break;
 
         case FILE_TYPE_FONT: