BebuLamar

I am not sure if I feel happy that the OP got it fixed with my rather dumb suggestion.

JimKing Loc: Salisbury, Maryland USA

The OP is tickled to bits.

JimKing Loc: Salisbury, Maryland USA

The unfortunate has occurred the problem is back. Removing the flash and replacing it has recreated the original problem. I've now taken it off and on several times and use my trusty pencil eraser to clean the contacts.

JimKing Loc: Salisbury, Maryland USA

When off the camera the flash fires normally with the test button and when on the camera the test button does not fire the flash and when the camera fires it there are the two pre flashes.

JimKing Loc: Salisbury, Maryland USA

More information: When the flash is on the camera and the camera is turned OFF the test button fires it normally when I turn the camera on the test button no longer fires the flash and firing the camera creates the two pre flashes.
Again: AGGGGH

JimKing Loc: Salisbury, Maryland USA

I've added more information and accidentally started a new post. I'm adding the new information to the old post.

The unfortunate has occurred the problem is back. Removing the flash and replacing it has recreated the original problem. I've now taken it off and, on several times, and use my trusty pencil eraser to clean the contacts.
When off the camera the flash fires normally with the test button and when on the camera the test button does not fire the flash and when the camera fires it there are the two pre flashes.
More information: When the flash is on the camera and the camera is turned OFF the test button fires it normally when I turn the camera on the test button no longer fires the flash and firing the camera creates the two pre flashes.
Again: AGGGGH

Bill_de Loc: US

If you were stupid you would have given up.

All's well that ends well.



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JimKing Loc: Salisbury, Maryland USA

It looks like I've repeated information that was not in a new post, sorry folks, but the problem remains unsolved.

JimKing Loc: Salisbury, Maryland USA

Thanks for the encouragement.

BebuLamar

Now I would want to fire the flash by using a piece of wire and short the contacts together to see if the problem is there.

TriX Loc: Raleigh, NC

And don’t clean the contacts with a pencil eraser. The gold plating on the contacts is quite thin and can be damaged by the abrasive of the eraser and it also leaves rubber residue. Instead, in the future use a contact cleaner (one without lubricant) available at your hardware store. I’d suggest wiping the contact down with alcohol to remove the eraser residue.

Now back to your issue. I can think of at least 3 reasons the flash might discharge multiple times (I’m assuming the shutter isn’t actually firing multiple times):
a) the camera and or flash is set to HSS. You stated you disabled it in the camera menu. Is the an HSS setting anywhere in the flash menu?
b) some cameras fire a preflash in low light to aid in focusing. Have you checked the menu to see if that could be the case?
c) and, as already suggested, it may be red eye reduction. Have you checked booth the camera menu (sometimes this is a selection in the “scene mode”) and the flash menu to make sure this isn’t enabled?

My guess is that there’s nothing unusual about the flash firing manually off camera and not on camera. Attaching it to the camera MAY disable the manual button for this particular camera and flash.

JimKing Loc: Salisbury, Maryland USA

a) When the flash on the camera's speed is set to 250 (Auto) the HSS indicator on the flash comes on, I've set it for 250 with no (Auto) and the indicator is gone . b) no pre-flash setting on the menus that I've found but I did try an outside shot and had the same 2 pre-flashes. c) have searched online and the manual for pre-flash with none found, and the D850 is a big guy with no scene modes. While my memory was never dependable in some areas, I believe the flash test button worked when the camera was on. And thanks for exploring options with me.

larryepage Loc: North Texas area

My D500 developed a problem a couple of years ago that wasn't too much different from yours. (It stretched out the whole automatic flash process, but would eventually finish the process OK.) It affected all flashes, but the problem was more severe with my SB-400 than with my SB-800. It gradually worsened until the flash system quit working altogether. Sent it to NikonUSA, where it was repaired (under warranty). They replaced the main circuit board, the flash circuit board and some interconnection cables (which I presume had some one-time-use connectors). I've had no problems since.

I also had a situation where another accessory (a 3rd party battery grip that others here swear by) simply refused to work properly with an older Nikon camera (a D300). Some of the functions worked great, others would not work at all.

My point is that these cameras are incredibly complex systems that have complex interfaces to outside systems. You may get to a point that rather than being continually frustrated, you are going to need to send your camera for possible repair. There's also a clear possibility that for some reason, this particular flash unit is just not quite compatible with your camera. My suggestion is that you try it, if possible, with a Nikon speedlight and see if it works ok. Is there someone in your area who has a Nikon unit that you might borrow? I would also suggest that you switch to a more "normal" flash mode and see if it works properly that way.

JimKing Loc: Salisbury, Maryland USA

I have used the Godox TT685n for 3 1/2 years with no problems. I generally use the i-TTL mode. Prior to that I used the Nikon SB600 until I physically broke it.

JimKing Loc: Salisbury, Maryland USA

Oh, BebuLamar I finally remembered to physically short out the fire terminal (center one) to the frame and it fired normally, just one flash.