Dropped frames at beginning of tapes

D

dcol64

Member
I have had a Canon XH-A1 for awhile now and always ran Sony tapes through it. Recently when capturing, the first 3 minutes or so of every tape I record on will drop several frames and stutter along at places. After that it's fine. Happens when capturing both SD and HD. Any diagnosis?
 
Basically, when a tape is being ran through the camera, its not going at a constant speed. The motor that's pulling it through is driving it from the center of the take up reel, and therefore, as more and more tape goes over to the take up reel, it goes through at a faster rate from the speed of the motor remaining constant but the circumference of the reel growing. So those first 3 minutes, its going through there slower, which is probably what's causing this. It's the same way that recording at LP makes the video more susceptible to getting dropouts than SP. When you try to record too much to a space on a videotape that's too small, it will drop out.
This has never been an issue for me with any camera though, my guess would be that if you tried cleaning the heads it would fix it.
 
A head cleaning might b e in order, but I suggest you familiarize yourself with the time honored tradition of pre-roll.
 
Thanks for the suggestions - I did try cleaning the heads but it did not help, and I understand the importance of preroll; my concern is that this just recently started happening after never being a problem before.
 
Hi

dcol64, your camcorders tape mechanism might be dependant of some kind of adjustment. Perhaps make a phone call to Canon and speak to one of their technicians.


Moseph, your suggestion that tape not running through the camcorder in constant speed is wrong. What happens is that the wheels containig the tape rotates in different speeds depending on whether it's an empty or a full wheel. The tape speed over the recording/playback head is allways constant:

HDV/SD (PAL): 18,83mm/s
LP (PAL): 12,57 mm/s

HDV/SD (NTSC): 18,81 mm/s
LP (NTSC): 12,56 mm/s


Regards,

/Bo
 
You're saying there's actually a sensor in there that tells the deck what speed to roll the tape through? You could be right for all i know, sounds strange though. I always thought the 18 mm/s was an average speed. I'm looking inside the deck of my schools A1 right now and I don't see anything that looks like it could do that. Is it based off of the same thing that lets you know how many minutes of tape are left (wherever that is)?
 
There are probably no sensors inside that you can see. The electric servo motor speed is controlled electronically by advanced cirquits that give the tape a constant speed with high precision. Otherwise it would bee impossible to align the rotating video heads correct over the tape. I also beleive that the video drum can be adjusted electronically to a certain level which is known as tracking. The electric signals are recorded in diagonally tracks over the tape, not as linear tracks. Each track is very thin so there is no room for variable speed, the speed has to be constant.
The reason you can see how much tape there is left is probably easy to calculate depending on the rotating speed of the two wheels containing the tape. If you know how fast they are rotating, a simple calculation will give the remaning length.

Regards,

/Bo
 
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