Just to be clear I am not a camera expert or dealer, I'm just helping an elderly friend clean out his house so he can downsize. This is one of several photography related items on offer.

Up for auction is this nice used Vivitar Auto Thyristor 550FD N flash unit for use with Nikon cameras. While I have not shot any photos with it, I did try putting batteries in (it takes 4 AA's) and when I turned it on I could immediately hear it power up. After a short time the ready light came on and I pressed the test button and it flashed, so it appears to work correctly.

Please see the photos to judge the condition for yourself.