Saturday, 4 May 2013

FIX: SB-800 only fires full power (or any other flash)

So your flash only fires full power? Or it kinda looks like it's even a bit stronger than full power?
I had the same thing happened to me. Twice.

When I asked, Nikon wanted I think $120 to get it fixed. Or more, I don't remember. The point is that I do not have the money to get it fixed.
So, I decided to try to fix it myself. And I did.

I did a bunch of research, and took my flash apart and put it back together several times, and I managed to not electrocute myself in the process.

Basically I found out that...
Oh, first: Disclaimer: I'm not some kind of certified technician, or trained in this kind of stuff. All I know I found out by myself, by experimenting and just generally being interested. The stuff I'm about to describe will FOR SURE void any kind of warranty, and it's also quite dangerous to do, considering that there is like 400V inside the capacitor of your flash, and you don't want that to go through your body.So I'm not responsible for any kind of damage that you or your flash or anything else might suffer in the process. In fact, I'm not responsible for anything you do. It's all up to you.
Advice: Before you start poking the inside of your flash with soldering irons and screw drivers, DISCHARGE THE CAPACITOR!!!! You can find how to do it in the repair manual on Page-9.
(HERE is the repair manual PDF)
Or alternatively, you can... well, this is a bit dodgy, but considering that your flash is dumping all the charge from the capacitor every time you flash, you can just press the test button, and RIGHT after the flash fired, rip the battery door open. This will not allow the capacitor to re-charge again. (this does not work if your flash is not broken the same way as described above. In case you have a working flash, you MUST discharge the capacitor as described in the above PDF.)

OK, so basically I found out that there are 2 components inside your flash that can be responsible for the above symptoms. (assuming you already tried the 2-button reset and it did not work)

One of them is a little black transistor, called IGBT. (Insulated Gate Bipolar Transistor). This guy is responsible for cutting off the electricity at the exact moment in order to provide the desired amount of light. If this transistor fails, it will not cut off the power, and will let all the electricity through the flash tube, therefore you end up with a nuclear blast, and an 8 second recycle, not matter what setting you are on. (even if you press the shadow button). This component can be found in pretty much every modern speedlight. (I know that many Canon flashes have it, and the SB-800 and the SB-50DX have it too.)

To fix this, all you have to do is to buy a new one, de-solder the old one from the PCB-B in your flash, and replace it with the new one... It's much easier to say, than to do.

There are some slight differences between SB-800s. They have slightly different parts inside. The number on the IGBT in my older flash is CT40TMH-8 (data sheet PDF), and it's made by Mitsubishi. You can find it on e-bay, and order it. It costs about $6+shipping. It's quite good compared to the $120 that Nikon is asking for. In my newer SB-800 it was a CT40KM-8H (data sheet PDF), made by Renesas.

The other thing that can go wrong is the fiber-optic-thing-whatever-it's-called. There is a little fiber cable that attaches to a photo-diode on the BCB-B. This thing is being held in place with a little metal thing. if the fiber optic cable is not properly seated in the housing of the photo-diode, or if it's broken, you will have the same phenomena as described above. Full power pops, no matter what.

This is because this photo diode is responsible for seeing when the flash tube lights up, and by seeing that, it does it's thing and eventually tells the IGBT when to cut off the power. If this photo-diode does not see the light coming on, it will also not tell the IGBT to cut the power, and you end up with a nuclear blast again.

To fix this, you have to take the metal piece off of the photo-diode housing, plug the fiber in as far as it goes (basically all the way, until it stops) and then put the metal thingy back on. If it does not hold securely, glue it in place.
if your fiber is broken, you are pretty screwed, and you have to find a new one that is exactly the same diameter and replace it. But I bet that it's also cheaper than $120.

With that, your flash should work now!

I'd check the fiber first, to make sure that it's not loose, before ordering the IGBT. It could be that there is no need to buy anything, just put the fiber back where it's supposed to be and then it's all good.

I hope this helps!

And feel free to leave comments if you have anything to say about this.


  1. Hi, First of all thanks a ton for writing such a detailed document in such a nice manner. The document explains all the points in a very very elaborate way and any end-user can do the repair work on his own. I am from India and my Nikon Sb800 has the same problem - always firing at full power. Nikon India is asking USD 140 for the repair and hence I have been searching in the internet for a repair guide or any other user experience. I am very much lucky to come to your blog. At first I checked the fibre, put it inside the hole very firmly and attached it to the metal clip by glue. But the problem is not solved - so I need to replace the IGBT. Now the problem is that my Sb800 is new version and the IGBT model is CT40KM 8H. You have already mentioned about it in the blog, but the last four digits (5708) are not matching at all. I have searched everywhere in the Internet and ebay; I am getting CT40KM 8H 0235 or any other CT40KM 8H XXXX - the last four digits different. So can I use any other C40KM 8H? What is the significance of the last four digits? Can you please explain? I will be very much grateful if you can answer my question and oblige. Thanks a lot in advance.

    1. Hello!
      I'm glad that you found this useful.
      The last four digits does not matter, as far as I know.
      Those numbers are different in my flashes too, and they both work fine.
      As long as the CT40KM 8H matches, the IGBT should work.

  2. My SB-800 has the same issue... It's been in a pool already once and i had it since 2004...

    I will try this and report back.

    Thanks in advance

  3. Hi,
    thanks a lot for this great info site!
    Have the same problem and currently on the way to fix it. The transistor seems to come also with an alias name RJP4301APP. At ebay you can get them actually for ~3,- to 15,- US$.

  4. Hi, wonder if you happen to know what the PCB E in the SB800 manual is for? It connects to the yellow connector on the main circuit board(PCB A).

    I couldn't power up my flash 80% of the time, so I opened it up to check if there is any loose connection or components. However, I accidentally broke one of the two pins in the yellow connector(Doh!) in the process. However, the flash seems to be working normally, minus the pin, after I put them back together.

    Thank you.