I have a JVC VCR, model HR-VP638U, which I bought in May of 1997, that I use for dubbing tapes on a very frequent basis.
About 10 months after buying it, it would sometimes display dropouts (white flecks) along a horizontal line approximately 1/3 or 1/2 way down from the top of the screen when playing back tapes.
I took this to the local warranty depot, and they replaced some brushes, ostensibly to eliminate static charge. According to the technician, this is a very common problem with this unit.
After getting the unit home, when playing back tapes, I noticed that the dropouts had increased excessively, not just along these horizontal lines, but all over the screen. It didn't make any difference what brand of tape I was using or what machine they were recorded on (either this JVC or my two other VCRs, a Toshiba about 4 years old and a Quasar about 8 years old). What was peculiar was that any tapes recorded on this JVC when played back on the other two VCRs and a fourth unit (a very old RCA one which barely works) were superb quality with no evidence of dropouts at all. In other words, the the dropouts only happen when playing the tapes on the JVC. Because of this problem, this unit is totally useless as a playback unit.
I took the unit back to the warranty depot, and the technician was unable to reproduce this dropout problem either with tapes I supplied or his own despite the fact that he had the unit for two weeks. I have never witnessed these results, but my son did during a previous trip to the warranty depot, and he reported that the tapes played back "normally."
Yet when I brought it back home ... the dropout problem when playing tapes on the JVC persisted.
I later did some research on the Internet at DejaNews where Usenet newsgroup messages are archived and found almost 450 messages from people complaining about this problem as far back as 1994. One of these messages is reproduced below.
Subject: Re: JVC Video From: webpa@aol.com (WEBPA) Date: 1997/10/17 Newsgroups: sci.electronics.repair >I have an annoying problem with (my own) 4head JVC video. >UK model HR-J725EK. JVC has built several machines based on a video headwheel design incapable of adequately discharging static electricity. This results in what is called "white comets" in the US. I own two machines with this problem: HR-S4900 and HR-S6900. They are S-VHS (North American) NTSC machines, but it is highly likely that the same headwheel assembly was used worldwide. There is a "repair kit" consisting of improved static discharge brushes to be installed under the headwheel is available (I have two kits sitting on my bench), but several people have posted to the NG that they don't solve the problem. The white comet problem superficially looks like dirty video heads or bad tape: white specks in the picture. But the comet problem is distinctly different from actual dirty heads. The "comets" do not appear at random locations in the picuture, the spots seem to briefly "hover" in approximately the same location in the picture, and they appear as streaks that start or end with a "head" wider than the streak itself. If your spots don't look like this, then you don't have the static discharge problem. Why does the problem appear with some tape and not with others? Contrary to some popular wisdom, there ARE significant differences among various brands of tape. The better (more expensive) brands include static-disbursing chemistry in the binder/oxide mix. Some have a coating on the back of the tape the serves the same function. Cheaper tapes skip these formulations. Naturally, most "factory made" videos are recorded on the cheapest possible tape...ergo, they are most likely to collect static electricity. This is not a problem except on JVCs vulnerable to the discharge problem. Further complicating the situation is the fact that the relative humidity of the atmosphere in which the machine is used also strongly affects the presence or absence of the problem. Finally, the real JVC white comet problem has no effect on recording, only on playback.Another poster offers the following advice:I own such a machine, the fault is in the design in the Video Head assembly. The Video Head is made of two basic parts sandwiched together. The two halves are joined electrically via Solderless connections, this is where the problem is. If the connections are not perfectly clean they will introduce noise in the video, sometimes intermittently with varying temperatures. Solution: Use a Flat-Tip "Jewelers Screwdriver" - Wiggle each of the Plastic Contact Keepers from the topside of the Video Drum, this will polish the connections. Take care and don’t twist/screw these Keepers, gentle repeated wiggles will do, otherwise they may break.
PROBLEM TIMELINE
May 5, 1997
Purchased the VCR.February, 1998
White streaks start to appear along horizontal lines. The problem is inconsistent, and disappears after a few weeks.Late March-April, 1998
The problem reappears. I take it in for service near the end of the warranty period. After about a week, I get the unit back. The problem persists, much worse than before. On the last day of warranty service, my son takes it back to the depot. The problem does not show up.Mid-May, 1998
I take the unit back to the warranty depot at their insistence. After two weeks, they have been unable to duplicate the problem. As soon as I get it home, the problem reappears.Early June, 1998
I send e-mail to JVC complaining about the problem via their Web site.Late June, 1998
Receiving no response, I send a copy of the above complaint to JVC by postal mail.Early August, 1998
I receive a call from the JVC head office in Toronto. They tell me to take the unit to a different warranty depot where it will be fixed at no charge.August 18, 1998
I take the unit to another local warranty depot. They fax JVC with an estimate for repair on August 24th and again on August 29th.September 9, 1998
According to the warranty depot, there has been no response from JVC. I fax JVC in Toronto a letter asking them why.September 15, 1998
There is still no response from JVC. I phone the head office in Toronto and speak to the person allegedly in charge of warranty service. He doesn't seem to know anything about my situation. However, he says he will contact the local warranty depot that afternoon.September 16, 1998
The guy from JVC finally phones them and approves the estimate.September 18, 1998
I got the unit home and played back several tapes and dubbed several more. It seems to work perfectly with both SP and EP tapes. Keeping my fingers crossed...September 30, 1998
Although the picture quality continues to be OK, there is now a slight crackle in the audio when playing back some tapes at both SP and EP speeds. When these tapes are played on other VCRs, there is no crackle, and the picture quality is excellent. The crackle can be eliminated by changing from Hi-Fi to normal sound on the JVC.November 16, 1998
Looks like the streaks have returned once again. I doubt if I'll bother to get it repaired one more time after the above hassles. At least it can be used as a slave when dubbing tapes (sigh).June 8, 2001
The VCR starts to make strange noises for no apparent reason (as if it was recording a tape, but there is no tape inside). The display on the front is flashing off and on. I play around with inserting a tape, and the display on the front is all wacky ... the tape will not eject, and when I try to remove it, it seems that the tape has wrapped around several things including some wiring, which gets damaged when I pull it out. The machine is totally inoperative as a result.