Replacing camera flash trigger MOSFET - 2SK2715

[Peabody]

While the pop-up flash on my Canon XT camera works fine, the hot
shoe doesn't work. So I took it apart, and found a discrete
transistor near the hot shoe, with one lead going to the hot shoe
center-pin connector, one going to ground, and the third going off
into the circuit bowels.

So I'm hoping this transistor is bad, and that's what's causing
the problem. The number on it is K2715P, which I assume is
2SK2715, a 500V N-channel MOSFET. That would make perfect sense in
this application.

But the problem is that the transistor is soldered onto that amber
flexible plastic stuff that passes for a PC board these days. I've
never attempted to desolder or resolder anything to that stuff. I
have a 30-watt iron. Can anyone give me advice on that?

An alternative would be to wire in the replacement in in parallel
with the existing part, probably just soldering to the old part
leads and trying to stay away from the plastic PC board as much as
possible. If I have room to do it that way.

And finally, this transistor appears to be pretty obscure, and
while Mouser carries it, it would be nice if I could use something
I'm more likely to find locally - an NTE part perhaps. It wouldn't
really have to have a 500V DS rating. As a practical matter, I
think 50V would be plenty - modern flashes don't go over 12V. So if
anybody knows of a common N-channel MOSFET that might work, please
let me know. But it has to be small. The body of the old one is
6.5mm wide.

Thanks for any help.

 

[Peabody]

larry moe 'n curly says...

Any luck finding a substitute in a power supply, such as
one for a PC? 500V MOSFETs are common in them.

I think you have to use a 500V transistor for the 12V
flash for the same reason vehicle ignition systems use
transistors rated for hundreds of volts on the 12V side
of the ignition coil -- big voltage spikes.

You could practice soldering the flexible circuit boards
of junked PC keyboards. I think they're made of mylar
polyester, while that brown flexible plastic in your
camera is probably kapton, a plastic with a much higher
melting point.

Thanks for the suggestions. I succeeded in desoldering the
Gate lead of the transistor so I could test it
out-of-circuit. But, it tested ok. So that wasn't the
problem after all.

However, after reassembly and doing a global reset of the
camera settings, it's working properly now.