Camera hot shoe trigger - Sherlock, help me deduce what this component may be

Apr 19, 2011 6 Replies

Yes, I know. It's elementary.



Well I have a Canon XT/350D DSLR, and the hot shoe doesn't work. The built-in pop-up flash works fine, but nothing fires in the hot shoe. So the issue is whether to attempt to take it apart, attempt to fix it, and reassemble without having parts left over. Aside from it just being a loose connection, fixing it would depend on the bad part being a discrete component that could be replaced with something similar. There are no schematics available, but here are some clues:


  1. When I measure resistance between the center contact and ground, with the positive lead on the contact, I get very high resistance. But with the leads reversed I get a diode drop.


  1. Since the popup flash works, it seems logical that the failure is fairly near the hot shoe in circuit logic terms. Otherwise, neither would work.

  2. There are warnings about trying to mount old flashes on modern cameras because the old flashes can have trigger voltages of several hundred volts, which can "burn out" the hot shoe. The Canon XT is rated to handle up to 250V.


  1. When I took the camera to a local tech for an estimate (5-145), he showed me the "top cover" assembly from a similar camera, and I saw up near the hot shoe a small three-terminal discreet device that looked like an SOT-23 package, with two leads on one side, and one on the opposite side. Of course it could have been related to the built-in flash, not the hot shoe.



So, back in the 80's when I was keeping up with this stuff, I would be thinking - it's a HexFET. I guess today it would maybe be an IGBT. But in any case, very probably a discrete component, and not a tiny one. And the replacement wouldn't have to be an exact match. In fact, all I really need it to do is fire a radio trigger, which is a 3V trigger drawing very low current. So I would have wide latitude in the replacement part.



And I found a video on YouTube showing the disassembly of a Canon XTi, which is a similar camera. It looks complicated, but not impossible. So I'm thinking I might want to give this a try.



Anybody have experience in this area who can give me some words of wisdom on what I'm dealing with here? Any info or suggestions would be appreciated.



Peabody Inscribed thus:

Is it possible that the flash head uses a trigger voltage of the opposite polarity to that required by the hot shoe ?

Best Regards: Baron.

Perhaps you will find something useful at this link:

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Or perhaps:

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My only other suggestion would be to see if one of the smaller pins on your hotshoe performs an "x-synch" function. Maybe you could trigger off this? (Not sure what Canon might call this. I think Nikon refers to it as FP-Synch?) Anyway, just a thought.

-mpm

Flash Program synch?

Sheesh.

Ahhh. So much information that has effectively been lost. X-sync and =46P-sync refer to old flashbulb days time versus intensity = characteristics. The functions remain the similar but the timings have changed to reflect electronic strobes. Hot shoes date back nearly as far and were = originally just metal contacts with timing related to shutter movement. About mid

1980s more hot shoe contacts were added to integrate exposure control = with the flash controls. Those other contacts do not carry normal flash trigger information. FWIW my first camera was a hand me down Kodak Autographic 120A folding bellows type. =20

Sheesh indeed. FP-synch is Focal Plane synch. Refers to the type of shutter. Of course, you wouldn't know that, being Always Wrong.

You probably had to google it.

Likely not the same function (or name) on all cameras either.

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