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Articles
Introduction
Camcorder Survival Kit
Maintenance Key With Metal Tape
Avoiding Head Clogs
Ikegami/Avid's Disk Recording System
Matchmaker, Matchmaker
A Call for Uniformity
The Ultimate Camera Standard
Looking Your Best
Video Head Evaluations
Sony
Investigates Betacam Camcorder Headwear Problems |
Sony Investigates Betacam Camcorder
Headwear Problems
TV Broadcast Alerts Sony To Increased Industry Concerns
By Mark Bell (contributing editor)
and Michael Silbergleid (editor-Television Broadcast magazine)
Sony's Betacam format, with
more than 300,000 VTRs and camcorders, is the workhorse of the broadcast
industry. But a trend has surfaced that, if not resolved, may adversely
impact the format's reputation. For the past few months, Television
Broadcast has been investigating premature headwear complaints-extremely low
hours before failure- reported by Betacam camcorder users, who reported that
the problem has become an expensive burden for broadcast stations, networks,
and freelancers.
The symptom manifests itself as an intermittent and undetectable (during
recording) error in the visual picture, referred to by broadcasters as an
upper-third chroma problem (or what Sony calls a "chroma flash").
According to Television Broadcast Engineering Consultants at Macie Video
Service, Dedham, MA, the problem appears to coincide with Sony's mid-1992
introduction of a redesigned Betacam camcorder upper head drum assembly,
commonly referred to as "heads."
According to Macie, the recording problem is most likely associated with the
new upper head drum assembly design. The specific cause of the problem is
now being increasingly investigated by Sony, based on reports given to them
by Television Broadcast and other sources.
A Change For The Better?
Sony's redesign of the camcorder upper drum assembly replaced a 3mm head tip
with a 1.9mm head tip. The change was to provide a 2db increase in the
signal-to-noise (an important increase for multi-generational users), while
keeping the same amount of head-to-tape contact on the head (according to
Sony, the entire 3mm head did not have tape contact).The first design of the
head drums with this change were found to have problems with chroma
head-to-tape contact, and were modified to the present model available-one
that has a "dual port" drum design. The problem appears as chroma dropouts
and tearing in the upper-third section of recorded video, and is
undetectable by any conventional RF alarm system during recording.
The problem does not affect all users of the new smaller head design, but
has been seen nationwide by videographers, news crews, and repair shops.
In a meeting held September 27, Television Broadcast and Sony discussed the
problem to try to determine its exact cause. From data exchanged at the
meeting, it appears as if there are still problems with both chroma
head-to-tape contact and wear. The history of camcorder headwear presented
by Macie indicated that problems requiring head drum changes are occurring
with as little as 141 head hours, with a majority of problems and premature
wear occuring under 500 hours-Sony's head-hour warranty period.
The pre-change 1992 heads typically lasted 800-1200 hours. At the present
time, Sony has accommodated customers' problems on a case-by-case basis
following investigation, although the exact cause of the problem is still a
matter of differing opinions.
At the meeting, internal memos acquired by Television Broadcast from one
network source were shared with Sony. The memos stated that the network
found the problem to be undetectable until playback of field tapes, and
intermittent enough to require spot checks. Included in the network memo was
a call to "roll back-up", stand-alone decks on important interviews." In
addition was the statement that a crew whose gear exhibited the problem
would not be sent out again until the camcorder was inspected by Macie.
Reportedly, the network has accepted camcorders whose heads have been
replaced by Sony as well. Interviews with other sources revealed the
problems were being experienced in television stations and production houses
nationwide.
'Worn' Heads or 'Bad' Heads?
Sony distributed a report during the Television Broadcast meeting regarding
heads that were replaced by Macie and turned in to Sony as
warranty/investigation material. The report stated that all of the heads
Macie replaced were not worn out, and were affected by a layer of "plastic
filming," a phenomenon that Macie supplied information about to Ikegami,
Sony, and Television Broadcast in February 1994. (Sony published a brochure
on VTR claaning that included this topic in March 1994.
Also in the report was Sony's assertion regarding one particular set of head
tips with a protrusion measurement of 17 microns and 8 microns, Y
(luminance) and C (chrominance) head, respectively, which were also on the
report as not worn. Heads when new, by Sony's information, have a tip
protrusion measurement of approximately 25 microns.
Macie claimed the "filming" was probably due to procedures in the
examination process, and has always been suspect as a cause for any problem
before diagnosis. Macie also claimed that if head tips are close to, or
below, 9 microns in tip protrusion, they will not provide network-quality
consistent performance. The importance of tip protrusion measurement in
headwear was one of the main areas of disagreement. Sony measures head life
by RF performance and head gap depth-not only by head tip protrusion. Macie,
and others in the industry, say that gap depth is not applicable in
camcorders, as that is not a true measurement of head reliability.
The reason why this head was serviceable was qualified by laws of material
physics by Sony engineers at the meeting. The fact that the original
problem, recording of intermittent chroma, was solved by replacing the
heads, with no other repair, was acknowledged for further study by Sony.
Sony did not acknowledge that the heads alone were the cause of the problem,
as many factors incuding tape tension, correct tape path, and alignment can
contribute to this type of recording error. Sony contends that replacing the
heads can mask another problem within the camcorder, while appearing to
solve the problem.
Historically, Macie evaluates all other camcorder parameters before heads
are changed.
Although not "worn," it appears to most technicians and users that the heads
replaced were "bad" in some way, as this solved the problem.
Sony indicates that original new heads with proper alignment in the
camcorder, shipped out of the factory, are not facing short head life. When
the upper head drum assembly is replaced, implementation of the tape path
alignment and tape tension alignment is a mandatory procedure.
According to Sony, the head condition can be judged by tracking a waveform (RF
performance). Before judging the end of head life, it is necessary to check
the head condition after using a cleaning tape. The regular use of a
cleaning tape is very important, or issues such as "plastic filming" can
mislead one to the conclusion that the heads need to be replaced.
One unfortunate industry practice is that preventative maintenance
procedures such as the use of a head cleaning cassette every 50 hours for
five seconds (as recommended in Sony's Technical Bulletin 95-182) and
re-equalization of the record current for optimal performance at 300-400
hours rarely takes place. This, no doubt, adds to the question of
determining the exact cause of the problems. (To aid in maintenance, Sony
has introduced the CLQ-30K, a non-CFC/non-alcohol formula Cleaning Kit.)
Additionally, Sony has a concern about those using isopropyl alcohol to
clean their heads. Common pharmacy isopropyl is actually less than 80
percent alcohol, which can leave residue. If isopropyl is used, Sony
recommends 99 percent isopropyl-as sold by electronics stores.
A Gradual But Increasing Trend
Although the new head drum design was first seen in mid-1992, the chroma/head
problem did not appear in the industry overnight. The trend was first
noticed in the Northeast, but other factors may have played a role since the
intoduction of the new smaller head tips. Freon, typically used to clean
heads, became less and less available between 1992 and now due to
environmental concerns.
One additional concern for Sony, which is looking for more data on this
problem, is the lack of heads available to test. One reason is Sony's
warranty of 500 hours or 90 days. This warranty, when averaged out, means a
crew would have to shoot 5-1/2 hours every day for the 90 day period. Repair
facilities have told us that although the head drum may have low hours
(below warranty specs), they are older than 90 days and can't be turned in
to Sony for warranty adjustment.
While Sony continues to investigate this problem, they urge camcorder users
with lower than expected head life to contact their Sony representatives.
Sony believes that, most importantly, the design change of the head tip
width has no relation to head life. Rather, correct alignment after drum
replacement and periodic cleaning of the camcorder tape path are the main
steps to prevent the symptom of chroma flash.
Television Broadcast will continue its own investigation into this area,
while Sony studies the cause of the problem. |
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