Nikon DSLR Shutter Release IO port, input stuck low

[sjetmand]

Hey everyone 

I have a simple optocoupler circuit for firing a dslr over hardwire.

Most DSLRs can be triggered over either a 2.5mm TRS plug or their own proprietary connector flavor with 3 pins. GND, Focus, and Shutter.

You generally have to tie the Focus pin to GND first and then hold Shutter to GND to fire the camera.

This optocoupler firing circuit has been problem free for over two hundred cameras. Suddenly, it sporadically fried the input on 3 Nikon cameras in a row (A D7100 and two D7200s).

The best I could find, after chopping up the 3rd party shutter release cable was a blob of solder on the Nikon N3 connector that appeared to have been intermittently shorting the Shutter and Focus pins together.

I can't for the life of me understand why that would cause this failure, but it's the best I've got because nothing else seems suspect .

I've replaced the cable, but am not trying to rule out possible repair of the cameras.

They are acting as though the Focus pin is persistently being held to ground. And since it thinks i'm holding the focus button, it disables the LCD, and won't let me do much except a full shutter press. So I can still take pictures. But I can't access the menu system etc.

I haven't taken them apart yet because they look like a veritable nightmare to re-assemble, but if someone thought it could be boiled down to replacing a single passive on the main board, I'll give it a go.

I'm attaching an image of the main board, from fixyourcamera.org ( http://www.fixyourcamera.org/nikon-d7100/ ) with the area in question highlighted.

Also, i've attached a picture of the connector and a different angle of the female jack on a pcb, I haven't worked out the pinout at the rear of the connector.

Any help = greatly appreciated.

Cheers! 

[voltz]

Cant see why shorting the focus pin to shutter release would cause a camera failure. Both pins are basically scanned Input pins. Usually scanned at 25Hz (maybe its 50Hz).. Have you tried putting a scope on each input pin and look for a logic square wave or maybe just a static HI ? If the focus pin is stuck Lo then it could be the protection diode for that pin. Used for static protection.
Only other idea might be to try a full camera reset, just in case this is a software issue.

[TiN]

Looks like there are 4 inputs with tinytiny ESD diodes and tinytiny 3-leg trannies coming from connector. Perhaps check those. Or maybe you just borked pullup resistor on focus/shutter lines?
Anyhow, be careful with soldering those HDI boards, they are very flimsy 

[sjetmand]

I guess the only thing to do now is set aside a week and crack it open.