It's definitely a GL646_HP.

unsupported/hp-scanjet-2400c.html

@@ -31,11 +31,11 @@
     </p>
     <h2>Chipset</h2>
     <p>
-      Maybe GL646_HP
+      GL646_HP
     </p>
     <h2>Comments</h2>
     <p>
-      If this is the GL646 chip, maybe the <a
+      Maybe the <a
       href="http://www.meier-geinitz.de/sane/genesys-backend/">Genesys
       backend</a> can be used, when it's finished?
     </p>
@@ -143,9 +143,10 @@ bNumConfigurations    1
     this is not a LM983x (bDeviceSubClass = 0xff)
     checking for GL646 ...
     this is not a GL646 (bDeviceClass = 255, bInterfaceClass = 255)
-    checking for GL660+GL646 ...
-    this is not a GL660+GL646 (bDeviceClass = 255, bInterfaceClass = 255)
-&lt;Couldn't determine the type of the USB chip&gt;
+    checking for GL646_HP ...
+&lt;This USB chip looks like a GL646_HP&gt;
+
+found USB scanner (vendor=0x03f0 [Hewlett-Packard], product=0x0a01 [hp scanjet scanner], chip=GL646_HP) at libusb:002:002
     </pre>
     
     <h1>Want to add or correct information?</h1>