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Canon XA and VIXIA Series AVCHD Camcorders
For the Canon XA25, XA20, XA10 and all VIXIA / LEGRIA Series AVCHD camcorders.

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Old December 4th, 2013, 05:47 PM   #1
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Join Date: Sep 2010
Location: Petaluma, CA
Posts: 14
XA-20 stuck zoom

Funny this should happen just after posting about the Libec zoom controller, but on an event shoot this morning, I experienced a stuck zoom, where the camera acted as if I was holding down the zoom rocker and not letting go.[Please do read this whole post before asking questions or offering suggestions.]

While recording, it wanted to zoom in all the way, and automatically returned to fully zoomed in if I zoomed it out and then let go. The Libec controller became completely non-responsive, although I could manually activate either of the zoom rockers on the camera. It became a constant battle to maintain a static shot, and the only way I could do it was to pull back on the zoom rocker on the camera just enough to counteract the zoom in (and even that didn't hold it consistently.) When I was finally in a position to pause the camera, it took over a minute to recognize the command. Then it wouldn't turn off or go into playback mode when I slid the switch on the camera, just stayed in pause. The only way to clear the problem was to disconnect all power and remove the battery for a couple of seconds. I was concerned that it was going to trash the last recorded segment written to the card, but it all turned out all right as far as that was concerned.

I'm thinking it was a lanc problem, but don't know if it's a defect in the camera or a controller problem. This is the second time this has happened.

Has anyone else experienced anything like this?

Alan Fitch is offline   Reply With Quote
Old December 5th, 2013, 06:14 AM   #2
Join Date: Sep 2001
Location: Northern VA
Posts: 4,357
Re: XA-20 stuck zoom

Do I understand that:
- the camera operated normally when the LANC controller was disconnected (at least after a system power-down reset)
- When connected the LANC controller acted as if calling for ZOOM-IN
- Is everything woring normally now?

It sounds as if the controller rocker switch or related position sensing circuit may have a defect (or even conductive dirt in it).

The first thing I would do is try a different (known good) LANC controller if you can find one. And try the controller in a different camcorder (perhaps try it on a demo model in a strore). This may help pinpoint the guilty soruce.

Camcorders are computer controlled by internal microprocessors. If the LANC terminal received "conflicted" commands from the controller it could have put the internal microprocessors onto a invalid state requiring a reset/reboot to clear it. (Kind of like computer crash or software hang.)

LANC sends commands, status, and time code (if implemented) information by setting specific bits in a serial data stream - a packet of 8 bytes if I remember correctly. This data stream originates in the camcorder. The controller works by pulling down specific bits in the stream that correspond to the desired command. The camera senses the command by reading the state of bits in the data stream and noting which bits are pulled down. The stream is repeated every frame, and a command must be sensed in consecutive frames to be executed. To cause the camcorder to keep trying to zoom the zoom command must be sensed repeatedly by the LANC terminal in the camcorder.

The LANC controller itself is a relatively simple device with a small microcontroller in it. It sends commands to the camcorder by monitoring its keypad and the data stream sent repeatedly by the camcorder. When a command key is presed, it waits until the data stream presents data bits corresponding to the command and short circuits those bits to ground (pulls them down).

In any case I do not recall encountered a simillar issue with any of my Canon camcorders.
Don Palomaki is offline   Reply

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