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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Replacing camera flash trigger MOSFET - 2SK2715
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. |
#2
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Replacing camera flash trigger MOSFET - 2SK2715
"Peabody" wrote in message ... 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. Can't you just snip off the body and solder the correct transistor (quickly) to those leads? Clamp something on the leads as a heatsink first. p.s. There is no way I would ever substitute a 500v rated component for a 50v one. Gareth. Gareth. |
#3
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Replacing camera flash trigger MOSFET - 2SK2715
Peabody wrote: While the pop-up flash on my Canon XT camera works fine, the hot shoe doesn't work. 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. 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. |
#4
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Replacing camera flash trigger MOSFET - 2SK2715
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. |
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