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Horizontal pixels missing in alternately

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clyde v
Horizontal pixels missing in alternately
on Nov 12, 2007 at 5:56:00 am

Hello everybody,

We have an old XL1 and it's exhibiting these problems. The problems show up from time to time. When the camera's being shot, everything appears normal as seen through the EVF. But when the tape is viewed either through the XL1 or through another camcorder, it looks like the camera can't record to the tape with all the fields. It looks like it's skipping every other horizontal field. Please check this out to see what I mean:

http://www.clydevillegas.com/problem_shots.html

What is the problem? Should I have the head aligned or replaced. (The guys at Canon told me they don't replace just the head but the whole recorder unit assembly) Is it the mainboard? Thanks guys.


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Don Greening
Re: Horizontal pixels missing in alternately
on Nov 12, 2007 at 8:55:54 pm

[clyde v] "When the camera's being shot, everything appears normal as seen through the EVF."

That's because the viewfinder isn't showing you what's being recorded, only what the lens is seeing. From your pictures it looks like a cleaning and adjustment is in order. Take it to a qualified repair facility. Only through testing will it be determined what is wrong and how much it will cost to fix. If the estimate for repair starts to add up it might be cheaper in the long run to get another camera.

- Don



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JoePM
Re: Horizontal pixels missing in alternately
on Nov 13, 2007 at 1:33:54 am

Hello Clyde -

Although this could be a serious problem, this also looks like it could be a simple instance of head clogging.

It looks to me as though one read/write head is not able to write to tape.

I don't recall if the XL1 incorporates a "flying" erase head just before the write head, but if it does, it would appear as though this head is clogged as well. That could account for the previously recorded material still being visible between the newly scanned video (your example #2).

In my past video life, I would never use video head cleaning tapes to clean S-VHS, U-Matic, or Beta decks, however, since the introduction of miniDV, I've been known to use them on occasion - particularly in the XL1. The head assemblies in those things appear to be so delicate, I'm a bit reluctant to clean them myself -- although I have several times with no problem.

Do you have a head cleaning tape? If so, use it sparingly. My Sony DVM-4CLD tape came with some MiniDV deck I had at work, and it recommends loading it into the camcorder, punching play and allowing it to run only about 10 seconds.

In fact, here is a tape vendor's description of the DVM-4CLD:

Head cleaning tape for Mini DV video cameras. Improve picture quality and sound by maintaining your camcorders heads. Insert the cleaning cassette into your Mini DV camcorder, press play or start button, after running the tape for 10 seconds press the stop button. Do not rewind the cassette after each use. Rewind the tape completely only after it has reached the end. The entire tape can be used twice before replacing with a new cleaning tape. Not suitable for recording.

Anyway, I would seriously look into cleaning this camera of yours before going to any great expense.

By the way, you didn't mention if this problem had occurred suddenly. Was one recording good and then the next one bad? Additionally, the fact that you appear to re-use tape suggests to me that this is a tape clogging problem. If at all possible, I strongly recommend against re-using miniDV tape. Particularly if you commonly use inexpensive, consumer grade tapes.

Finally, and sadly, given your example #2, I don't think it is likely that your recordings are intact. I have witnessed similar problems where the playback was all segmented such as yours, but the problem existed only in a playback deck, and the original recording was complete. A cleaning of the playback VCR revealed that the original recording was okay -- quite a relief. But, in your situation, the fact that previously recorded video has not been recorded over would suggest that one set of heads was not functioning properly during the record process. Sorry.

I hope this helps. Good Luck.

By the way, this is my first reply to a post on Creative Cow. Sorry for its length.

Joe


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clyde v
Re: Horizontal pixels missing in alternately
on Nov 13, 2007 at 2:24:18 am

Thanks joe. That's very informative. About the problem happening suddenly, yes it did. The first time it happened, I just ignored it because after pressing the start button, the next footages were ok. After a few weeks, it happened again. Yesterday, I shot the XL1 and the problem did not occur. What worries me is that it might happen during an event coverage. I am thinking of replacing the whole recorder unit. What do you think?


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JoePM
Re: Horizontal pixels missing in alternately
on Nov 13, 2007 at 6:36:21 pm

I completely understand your fears about not wanting a failure to occur during the recording of an event. Few things in this line of work are more upsetting than that.

Still, a replacement of the recording unit seems premature to me unless the head cleaning possibility has been fully investigated. If it has been, then you are probably correct to want to change the recording unit in an effort to obtain confidence.

I'm not quite clear as to whether or not you ever cleaned the heads after the first occurrence of this missing field anomaly. If you didn't, it is still possible for the unit to "correct" itself the next time the camcorder is used, either for playback or recording.

As you may already know, head clogs usually occur when oxide scrapes off of a tape and lodges against one or more of the heads in the spinning head drum assembly. Sometimes such clogs remain trapped where they are as long as a tape is pressed against the drum. Eject the tape, and sometimes the offending particles of oxide fall away from the head drum, and the next recording will be okay.

Sometimes, loose tape debris will remain within the tape transport area, and re-lodge against ahead and "bingo" you've got another messed-up recording.

Typically, if I see this type of problem occur and then reoccur, I will first look at my procedures to see if I am using a particular tape just prior to the incidences of failure. For example, are you using your camcorder to capture from some old, heavily used, miniDV tape that might be decomposing and dropping off debris?

Then, are you shooting again, possibly even with new tape and experiencing this "missing field" problem, because the older tape left dirt behind. You might have an offending tape that is getting passed through your camera that needs to be retired.

Again, if you have never cleaned the heads after these bad recordings first appeared, then my opinion would be that you would be jumping the gun to have some service center simply replace the recording assembly.

Also, have you been recording (prior to, or during these failure events) under extreme dust conditions? For example, have you been shooting around saw dust, or during high-wind dust storms. If so, these too can certainly lend themselves to these sorts of failures, and head cleaning is again, step number one.

Finally, there is one thing that leads me away from my own head clog theory, a bit. That is the fact, that I believe the XL1 incorporated a feature that would allow it to put up a display in the viewfinder, instructing you that a head cleaning was needed. "Heads dirty, use cleaning cassette."

This message has been notoriously unreliable, however, as it has often appeared on brand new cameras.

Clyde, if you google the following: "Heads Dirty, Use Cleaning Cassette" XL1

you will find several posts by people who describe similar "striping" issues to what you are having. See what they have to say.

Although there is a lot of disagreement, I think most pros recommend head cleaning at around every 50 hours use, unless shooting in extreme dust conditions which naturally requires more frequent cleaning.

So bottom line, are you cleaning the heads?



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clyde v
Re: Horizontal pixels missing in alternately
on Nov 13, 2007 at 10:30:10 pm

I cleaned the heads. Then after recording about 5 tapes, the striping happened. And yes, I've used it in a windy environment when I was shooting in a container yard beside a sea.


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clyde v
Re: Horizontal pixels missing in alternately
on Nov 13, 2007 at 10:30:41 pm

I cleaned the heads. Then after recording about 5 tapes, the striping happened. And yes, I've used it in a windy environment when I was shooting in a container yard beside a sea.


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JoePM
Re: Horizontal pixels missing in alternately
on Nov 14, 2007 at 4:10:20 am

Man, I was hoping you were going to say that you never clean the heads on your camcorders, and then we could all shout "that's the problem."

Still, I feel like something strange might be going on. I don't want it to sound like I'm trying to lay the blame at your feet, but I must ask if those five good tapes shot after head cleaning were repeat-use tapes?

Also, I don't know what the rules are here about posting quotes from other sites (I suspect it's frowned upon) but solely in the interest of helping, here are three comments from other miniDV users that might apply:

"Also, in case you weren't aware, it's considered bad practice to switch brands of tape. So, whatever brand your first tape is, try to stick with it. There are differences in the tape formulations between various manufacturers that when mixed, can gum up the heads."

and also . . .

"Choose one brand and stick with it. Clean between brands if you must switch back & forth."

and finally . . .

"Brian from Zotz Digital told me they only sell and recommend the Panasonic DV tapes since it's the only brand that does not use oil based lubricant. I couldn't say why this is better though, I'm fairly new to the DV world."

Personally, I am not that careful about switching between tape brands, and I've not had routine clogging problems, but this situation seems to be commented on so often on-line that I assume it is real.

Do you think it is possible that you are experiencing this "change of tape brand" problem, or do you stick with only one brand?

Finally, your comment about shooting at the container yard has been weighing on me. Windy conditions alone should not adversely affect the XL1, but if a large amount of dust was in the air, you might be in need of sooner-than-average head cleaning.

Of more concern to me is the possibility that the camera might have been exposed to a lot of saltwater mist. Was it at this seaside location that one or more of your five good tapes were shot before the striping problem reappeared?

I've known of camcorders that were used to routinely tape swimming events at chlorinated pools that wound up with head drums that were scarred and pitted and eventually the associated heads failed. Apparently the chlorine in the air around the pool was corrosive enough to damage smooth internal parts.

Of course, this was a freshwater swimming pool, so the circumstances aren't identical, but I suppose it would not have been impossible for saltwater mist to have damaged the surfaces of the drum and head. Still, I find this unlikely.

You might visually inspect the head drum of your XL1 to see if the drum surface is still mirror-like. If not, you might actually be looking at something greater than a cleaning problem.

Do you mind my asking if you've been given an estimate as to the cost of replacing the entire recorder section? I'm just curious. I still hope it doesn't come to that.

Good Luck!

Joe


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clyde v
Re: Horizontal pixels missing in alternately
on Nov 14, 2007 at 4:57:06 am

The first two or three tapes are new ones. The next tapes were re-use tapes. The entire recorder unit is about USD350, but that's only an estimate. The Canon technician cannot tell how much it is exactly.

The XL1 manual instructs users to clean the heads before an important shoot. What if all your shoots are important corporate videos? Does that mean cleaning the heads on every project? Don't you think doing that will abrade the heads?


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Don Greening
Re: Horizontal pixels missing in alternately
on Nov 14, 2007 at 9:33:23 am

These questions have come up numerous times in the Canon and other forums. Just do a search for "head cleaning" or something similar. Meanwhile, you may want to read this:

http://forums.creativecow.net/readpost/11/855340&pview=t&univpostid=855340

- Don


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