Maybe not totally on topic, but I can post a pic here, so I hope
it's ok.

So I'm trying to fix the hot shoe on my Canon XT, and there's a
good chance the problem is the transistor which appears to be
driving the center terminal of the shoe. Of course I don't know if
that's the problem, but it appears to be the only thing I could
fix, so I'm gonna go with it. :-)

As shown in the attached pic, this is a K2715P, which I think is
really a 2SK2715P, a high-voltage N-channel MOSFET. But, it's
soldered to that flexible amber circuit stuff. Is it reasonably
practical to desolder the old part, and re-solder the new one,
without destroying the plastic?

If not, I'm thinking I could perhaps leave the old part in place,
and parallel in the new one - if there's room to do that - and just
solder to the leads of the old part. Carefully.

One more thing. Despite the "P" package designation, in the data
sheet Rohm says it's a "TL" part. Mouser calls it both CPT and
SOT-428. Can anyone make sense of these packages for me. The old
P part is about 6.5mm wide.

Thanks for any help.

Forgot the pic. Here it is.

Peabody wrote:
....
Is it reasonably
practical to desolder the old part, and re-solder the new one,
without destroying the plastic?

No.

If not, I'm thinking I could perhaps leave the old part in place,
and parallel in the new one - if there's room to do that - and just
solder to the leads of the old part. Carefully.

Clip the leads to leave at least 1/4" to 3/8" of bare lead soldered
in. Get a heat sink, like a forceps or a big alligator clip, clip
the lead at the base, trim the leads of the new part, and just sweat-
solder the leads together.

Good Luck!
Rich

Peabody wrote:

Forgot the pic. Here it is.

Oops! In my other answer, I ass-u-me-d that you had a TO-220 or so.

This can probably be done, with a lot of care, and if the alternative
is to toss the whole thing, then go for it, with a lot of care. Get some
solder-wick to soak up the solder, and just do it. With care, of course,
so that you don't melt the substrate.

Good Luck!
Rich

On 4/20/2011 4:11 PM, Rich Grise wrote:
Peabody wrote:

Forgot the pic. Here it is.

Oops! In my other answer, I ass-u-me-d that you had a TO-220 or so.

This can probably be done, with a lot of care, and if the alternative
is to toss the whole thing, then go for it, with a lot of care. Get some
solder-wick to soak up the solder, and just do it. With care, of course,
so that you don't melt the substrate.

Good Luck!
Rich


Actually, your suggestion to clip the legs is still a good one. Clip the
two small legs first, then unsolder the tabbed end. Then remove the
remainder of the smaller legs.

Cheers,
John

Thanks very much for the replies.

I decided to try to desolder the Gate leg so I could test the
transistor out of circuit, so to speak. Well, I didn't actually
desolder, just heated the pin and pulled it off the plastic.

But to my surprise, the transistor tested perfectly. So, that
wasn't the problem.

But the good news is that upon reassembly and resetting the camera,
everything works perfectly.

Don't need brains if you have good luck.

Clipping the leads on this package is sometimes a problem. Using a diagonal
cutters causes the leads to push apart as they separate. This often causes
the pad to rip from the substrate. If you use this method, try to cut on the
vertical to board portion of the lead.
For thick leads, I sometimes remove the bulk of the solder with a wick and
then with heat and a slight upward pull from a hook tool, lift the lead from
the pad. This requires a deft touch and heating as you're just as likely to
lift the pad. I've also used a dremel tool with a cutoff wheel to cut the
pins from the package. Downside of this method is that you get conductive
dust everywhere.

Oppie

Clipping the leads on this package is sometimes a problem. Using a diagonal
cutters causes the leads to push apart as they separate. This often causes
the pad to rip from the substrate. If you use this method, try to cut on the
vertical to board portion of the lead.
For thick leads, I sometimes remove the bulk of the solder with a wick and
then with heat and a slight upward pull from a hook tool, lift the lead from
the pad. This requires a deft touch and heating as you're just as likely to
lift the pad. I've also used a dremel tool with a cutoff wheel to cut the
pins from the package. Downside of this method is that you get conductive
dust everywhere.

Oppie

On Wed, 20 Apr 2011 14:11:42 -0700, Rich Grise wrote:

Peabody wrote:

Forgot the pic. Here it is.

Oops! In my other answer, I ass-u-me-d that you had a TO-220 or so.

This can probably be done, with a lot of care, and if the alternative
is to toss the whole thing, then go for it, with a lot of care. Get some
solder-wick to soak up the solder, and just do it. With care, of course,
so that you don't melt the substrate.

I might use solder wick to clean up, but something like that I'd heat with
tension on the chip (glue some string to it or something). Get the chip off
that film circuit, then worry about sucking up excess solder.

For the tab, make a good heat bridge to the top of the tab, go for it, the
two legs will already be preheated by the time you get to them, not need much.

Good Luck!

Yup, and use a good iron, low temperature with lots of backup, a big tip
job for thermal mass.

Low temp gives you a couple tries, temp too high and you fry something.

You can always stop and start over after the thing cools, if it doesn't
feel right first time.

Rich