Nikon SB-910 random black frames

[MEPER]

I have experienced some problems with a SB-910 flash.
I have two. One with flash head fixed to 24mm and showing err in display. That flash works perfect.
Then I have another where I hoped everything worked but it gives me random very dark frames.
Same with different lenses and different bodies. I have also reset the flash to be sure it was not a kind of "bad" setting.
Most frames are ok. When error happens the red flash indicator flashes like the there was too little flash-output. But that is not the case. It seems to be a synch issue.
Error can happen also on 1st frame after flash indicates fully charged. Also my test images I used something white very close to be sure flash was not "exhausted".
I have added a "good" and a "bad" frame. I have overexposed in NX-Studio the "bad" frames with 5 EV's just to show that there are some information in the image.
Any guess what can be wrong?   
I have cleaned the hot-shoe contacts. Maybe an internal bad connection or an electronic failure?
Can something be seen from the EXIF-data of the attached images?

[Birna Rørslett]

My first suggestiomn is dropping the 'X' speed from 1/200 (or 1/250, depending on model) to say 1/160 or 1/125 sec. You might experience synch issues flash-camera.

If that doesnt help, let Nikon repair techs dissect your fash unit.

[MEPER]

I think I have come a little bit closer to what could be wrong with the flash unit.
If I set it in RPT (repeat mode) and select e.g. 24 times, 10 Hz. Then on the good unit if I press the red led test button there comes a 10 Hz burst that last 2.4 sec. as it should.
On the bad unit the burst is only 1-5 flashes. Before it stops.
Maybe a bad capacitor or the charge-unit that does not charge the capacitor to full voltage?
Probably a leaky/bad capacitor?

I will start my complain to the Ebay-shop where I purchased the flash. It is a real physical shop in Germany and I have a real invoice and can contact them directly.
For fun I looked for a repair video where the capacitor is replaced but no luck so far. It is also difficult to find a new replacement capacitor. I have found a used one at Ebay in USA.
It is a 1700uF / 350V type but I don't know the exact dimension to try to find a 3. party capacitor.
Most repair videos shows how to replace the flash bulb tube. But first I will contact the shop.

[HCS]

Not an owner, nor expert, of the SB900, but have used the SB800 and SB600 a lot.

Just checking: fresh batteries, ready light on before releasing the shutter?

If that's the case, i'm with Birna, probably capacitator and back to Nikon it should go.

One last trick to make sure it's not bad contact in the hot shoe, is to feel the "wobble" of the unit in the hotshoe. If it indeed does wobble (i've had that before), a little and careful re-adjusting the hotshoe "rails" might help out. Be careful though!

[MEPER]

Batteries are fresh. I use Panasonic Eneloop. I also just to be sure used 100% fresh alkaline. The other 910 unit I have works perfect with Eneloop.
The red led turns on very fast. Flash unit fails already as not connected to camera just using the test button in RPT-mode where burst is way too short.

[MEPER]

I wonder if I would be able to use the SB-900 repair manual (too large to be attached but easy to download it for free) to get into the photo flash capacitor in a SB-910 unit?
Nikon calls it a "condenser". At page D33 is shown how to get the cap out.
It looks like a really hard and time consuming job. Maybe fast for a person who do it every day.
Not sure I would like to spend all the time needed and also I need a spare capacitor. What I could test is if the capacitor reaches the spec'ed voltage at the de-charge terminals just below the rubber pads.
First I will se if the photo store answer back at my email.

[HCS]

I wonder if I would be able to use the SB-900 repair manual (too large to be attached but easy to download it for free) to get into the photo flash capacitor in a SB-910 unit?
Nikon calls it a "condenser". At page D33 is shown how to get the cap out.
It looks like a really hard and time consuming job. Maybe fast for a person who do it every day.
Not sure I would like to spend all the time needed and also I need a spare capacitor. What I could test is if the capacitor reaches the spec'ed voltage at the de-charge terminals just below the rubber pads.
First I will se if the photo store answer back at my email.

I, for one, couldn't do this myself. If you're a trained and skilled technician, you might.

I concur with emailing the photo store first 

[MEPER]

I have contacted the shop in Germany and they where responsive.
I got a link to a template to start-up a return process. After than I got a mail with a new link to a template to fill-in and after than I got a mail with info how to return the item (specific address etc.).
It is sent for repair with a description of the problem. I doubt they will repair it......but we will se. It is an Euro 200 2nd hand item and an official Nikon repair will be much more than that is my guess. Two hours work and new spare parts?   
But first the flash has to be shipped to Germany and the store has to accept the problem description.

[MEPER]

The German photo store just refunded the flash when they got it back. No repair :-)