I have a Nikon SpeedLight SB-700 that I’ve had for years. During a recent shoot, it went dead after the first flash. I had light corrosion around one of the battery contacts, but nothing that looked like it would impede the current of the battery. But it definitely was. I tried alcohol on the contacts followed by pencil eraser, but no luck.
Here’s how I was able to fix it:
1) Lightly rubbed the contacts with a 2cm x 2cm square of 120 grit sandpaper and taped to the end of a rounded pencil eraser.
2) Spray a light amount of CRC Contact Cleaner using the red straw-nozzle on each of the battery contacts.
3) Dry the battery compartment with a bit of compressed air. (I used an air compressor so I tried to be gentle with the air, so as to dry the contacts and any residual contact cleaner, but not to dislodge anything inside the flash body.)
That did the trick! 4 fresh Alkaline batteries and voila! I’ve fired about 10 1/1 bursts and everything seems to be working just fine!