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Black screen on D-VHS playback  

post #1 of 9
Thread Starter 
One of my Panasonic STB/VCR combos recently started to exhibit a problem that is becoming progressively worse.

The STB recognizes that a D-VHS VCR is connected, but sometimes it produces only a black screen on tape playback (started from the VCR's
front panel). The "D-VHS Playing" indication always appears on-screen. Sometimes the channel number indication ("DTV 1-1") also appears, but
sometimes not. Generally I can correct this by stopping playback and starting it again. But it's gotten to the point where it's sometimes necessary to start/stop several times before playback is successful.

At least once, playback began successfully but after a few seconds the image froze even though the tape continued to play.

This sounds distressingly like there's some problem with the Firewire connection. If so it will be difficult to fix without sending it back to Panasonic, which I'm reluctant to do because they take many weeks to complete servicing and (in my experience) don't always do a good job anyway.

Has anyone else here seen these symptoms? Is there anything else I might try to arrest the problem?

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Ron Gomes
post #2 of 9
Could maybe be the heads. Mine was doing some stuff like that. Can you play a tape that you know is good?

dave
post #3 of 9
Yup, sounds like either dirty or worn video heads. I would first try a good manual cleaning, don't try this unless you know what your doing, or a local repair shop should be able to do it.

If that doesn't work, take a look at this: http://www.avsforum.com/ubb/Forum28/HTML/000226.html

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"Better living thru modern, expensive electronics devices"
tm
post #4 of 9
Thread Starter 
The problem isn't tied to individual tapes; in general tapes will play without problems in my other combos.

I've already replaced the head assembly in one of my PV-HD1000s and had decided (separately from this problem) to do the replacement on all of them even though it's not cheap. I have the heads on order, in fact.

I don't remember reading here about this particular problem in connection with worn or clogged heads. The problems I saw on my other unit (before head replacement) were tiling, green flashing, and other indications of dropouts. And the head replacement did indeed seem to correct that.

But this misbehaving VCR, though purchased new a year ago, has more hours on it than any of my others, and I can certainly believe that its heads are worn. When the new part arrives I'll install it and see if that clears up the problem. I hope it does.

I've said this before, but I'm so weary of the problems with these units. The problem with having so many of them is that something is always broken. One of my STBs now has an intermittent antenna input connection and I'm going to have to send it to Panasonic for repair.

But within a few weeks things should be in a state in which all the STBs have been refurbished by Panasonic, and all the VCRs have new head assemblies, and I'm hoping that things will then be fine for a while.

Things would be so much simpler if I didn't find HD recording such a compelling hobby. But I do (for now) so I'll keep feeding it for a while.

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Ron Gomes
post #5 of 9
Thread Starter 
I've now replaced the heads in the VCR of the misbehaving combo. Although there's an improvement in the playback performance on previously problematic tapes, the head replacement does not appear to have fixed the original problem (intermittent black screen on playback, sometimes requiring that I stop/start several times before the digital stream is noticed and properly played back).

If I connect the VCR (with new heads) to a different STB, the behavior is the same, and it's also the same if I use a different FireWire cable.

This suggests a problem with the FireWire connector on the VCR, does it not?

As things stand now I either have to live with this problem and hope it doesn't get worse, or else I have to ship it back to Panasonic for repair--and I don't have high confidence that an intermittent problem such as this will be successfully diagnosed and repaired by Panasonic.

If anyone here can think of a practical alternative, I'd appreciate its suggestion.

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Ron Gomes
post #6 of 9
Ron-
Have you eliminated the possibility of 1394 intermittant connection? My 1394 cable from Panasonic has those huge toroid chokes and these can put a strain on the connections. I have mine properly held in place to eliminate this stress.

I also have another question regarding your use of these PVHD1000's. You have more than one. How many hours a day do you typically get on one machine? I only have one machine here and I may record 2 or 4 hours a week anymore. There just isn't that much new stuff to tape considering I now have close to 300 tapes recorded. (Haven't counted lately) My point is that using similar mechanics as a consumer VCR im my dub rack for duplicating my own products, I run 15 machines on the average of 5-6 hours a day and these last over two years. Usually the heads are not worn out but the power supplies and pinch rollers are the things that go first. I have had a couple VCR's that the heads wore out in 3 years which is about 3000 hours of use. If you are getting less than 3000 hours on your heads I'd say you are doing something wrong, but not sure what that would be.

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Don Landis
Home Theater Pics at: www.scubatech.com Last updated 3/25/01
post #7 of 9
Ron,

A few quick questions:

1) Do tapes made on the defective machine always play properly on other machines?

2) Does the defective machine have the same problem starting playback with tapes made on itself as with those made on other machines?

3) Does the start problem only occur at the beginning of a tape, or can it also occur at the middle or end?

4) Does stop/start always fix the problem if done enough times, or is it sometimes necessary to eject the tape. Or is it necessary to wiggle wires, bang on things etc.

5) Do you have a service manual?

6) Are the tapes you use new or used?

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-Roger
Analog -- Always out of adjustment.
Digital -- Always one more bug.
post #8 of 9
Thread Starter 
Don: because of the symptoms I do suspect some kind of intermittency in the 1394 connection, but the evidence suggests that the problem is not with the STB or the cable. I've tried to orient the cable connections so as to reduce stress on the connectors, but I've also tried a non-Panasonic cable and the problem persists.

From other postings in this Forum (Roger's, I think) I had gotten the impression that the digital heads on a PV-HD1000 were good for something more like 1000-1500 hours rather than for 3000. The first VCR on which I replaced the heads had been purchased used, and I have no idea how many hours of service it had seen. But it was definitely exhibiting the dropout, "green-flashing", and end-of-tape problems so often described here. The head replacement cured those problems.

As for how much use the VCRs get: rather a lot. I'm taping most of the HBO and Showtime movies and timeshifting some network HD. The problematic VCR, the one I'm discussing here, was bought new a year ago and has gotten more use than any of the others. It could certainly have accumulated more than a thousand hours in that time.

Concerning Roger's questions:

1) Tapes made on the misbehaving machine will generally play properly on other machines, yes. (Without anything like the stop/start problem, if that's what you mean.)

2) Yes, the start/stop problem is present regardless of the source of the tape. It happens with tapes recorded on the defective VCR as well as those recorded on others.

3) I believe I've seen the start/stop problem occur at various positions on the tape, but it's been a while since I checked that. (Most playing is done from the beginning, naturally, and once playback has begin successfully it usually continues that way without interruption.)

4) I haven't attempted any wiggling or banging. I've tried removing and replacing the FireWire cable but it didn't affect the problem in any obvious way.

5) No, I don't have a service manual. (Perhaps I should.)

6) The tapes I use for recordings are always new, or have been used at most a few times. Mostly I use Fuji ST-120 S-VHS tapes (originally Don's suggestion), which work well for this application.

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Ron Gomes
post #9 of 9
Ron,

I think I'd replace the pinch roller, and possibly the tensioning device.

When play mode is started the tape has to get to proper speed and tension quickly so the circuitry can decide whether the signal on the tape is DVHS or VHS. If the tape slips initially on the capstan the recorder might stay in VHS mode, and never lock to the digital signal.

Just a guess. I haven't seen this in my stable yet, although I have had some tapes that didn't like to start.

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-Roger
Analog -- Always out of adjustment.
Digital -- Always one more bug.
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