Since I don't have a Pro-96 or the service manual, I can't guarantee my answer but chances are good this is the "reverse polarity protection diode" that's designed to blow quickly when power to the scanner is supplied with the polarity wrong (positive where the negative should be and vice-versa).
This can happen quite easily when using one of those common "adapt-a-plug" supplies. These plugs are "wall warts" sold by companies, like Radio Shack, where you get the wall wart that provides the correct voltage and current and then purchase the correct plug for the device you plan to use it with. The various plugs all have a common connection on the side the connects to the wall wart and different outside and inside diameter connections to mate the device it's being used on. Since the polarity is selected by plugging the plug into the wall wart's cord one direction for a center positive and the reverse direction for a center negative connection. It's easy to get this wrong and damage your device.
Several manufacturers have designed their equipment with a reverse polarity diode across the power connection so when plugged in correctly it doesn't conduct, but when the polarity is supplied in reverse, it conducts and quickly destroys itself, preventing the incorrect power from damaging the device beyond the easily replaced diode. This is why I guess that diode appears to be damaged and the scanner no longer working. It should be a fairly quick and cheap repair to replace it and get things working again. Unfortunately, that probably would require a service manual or schematic.
My beef over this type of protection is the protection is basically a suicide protection and requires a service call to repair the damage. Sure the diode is cheap, but you'll pay more for shipping and service fees than the diode costs. Now, if they'd spend a bit more ($0.25 instead of $0.10) and used a full wave bridge rectifier chip instead, it wouldn't make a difference what polarity the supply was, it would simply work and a reverse polarity problem would cause no damage, nor even be noticed.