SB900 SB910 Differences - maybe cause of overheating and possible solution

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iforland
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SB900 SB910 Differences - maybe cause of overheating and possible solution
3 months ago

I love playing around with broken electronics and have become quite good at repairing them.

So recently I managed to get hold of a broken SB910, I've already fixed many SB900's but I always wanted to know why these overheated and the SB910 didn't.

So the opportunity to open up an SB910 and investigate was something I couldn't turn down.

Anyway the two flashes are virtually identical inside, pretty much all of the electronics are the same apart from one significant area, shown in the pictures below:

SB900

SB910

And a couple of side views to help explain the context.

SB900

SB910

A little bit of an explanation first, the bits that you need to be looking are where the big red wire is connected. This is where the power from the batteries comes from. Both flashes have two thermal fuses (Which I haven't shown very well - if you look at the orange wire you can see the ends of them) but the SB900 has an extra one (The large cylinder/resistor like object that's marked "0875" in the very first picture and is what the red wire is connected to. This is bonded to the large metal heat sink.

Now the theory, as the flash is used not only do the batteries heat up but so do the thermal fuses, obviously if they get too hot (this normally if there is a fault) then they blow (like a normal fuse) and the flash is dead until you replace it. However they do get very hot with normal use, and so does the heat sink and the internals of the flash.

Now it looks like in the SB910 that they have removed this third thermal fuse, and increased the heat sink size.

The idea is to remove the fuse from an SB900 and see if its performance is improved.

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