Notes on the Troubleshooting and Repair of Video Cassette Recorders


[Document Version: 2.77] [Last Updated: 05/25/1998]

Chapter 1) About the Author & Copyright

Notes on the Troubleshooting and Repair of Video Cassette Recorders

Author: Samuel M. Goldwasser
Corrections/suggestions: | Email

Copyright (c) 1994, 1995, 1996, 1997, 1998
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.

Chapter 2) Introduction

  2.1) Entertainment - then and now

Note: A version of this document and "VCR First Aid" may also be found at
the VCR Flashbook: Interactive VCR Manual web site.  The content is
similar but you might prefer the style of that web page.

Think back 20 years.  You went to the theater to see a movie.  You watched
TV programs when they were broadcast (there was no cable, remember?) or you
missed them.  TV studios and industry had video recording equipment but it was
expensive and cumbersome.  Little did you realize at the time, but after
some false starts, the modern video revolution was about to be born.  Are
we better off?  Whatever you decide, there is no going back.  You may be able
to leave your VCR's clock flashing 12:00 but you cannot escape the impact
that this technology has had on so many aspects of your life.

The video cassette recorder is a wonderful example of extremely complex
precision technology that has been made affordable through mass production.
In general, it is usually quite reliable.  Treat a modern VCR with a bit
of respect and it will provide trouble free service for a long time.
Unlike a TV where the power circuits take their toll on circuit components,
the electronics in VCR are generally quite reliable and rarely fail.  Most
VCR problems are mechanical - dirt and dust in the tape path, deteriorated
rubber parts, dried lubrication, wear of precision parts including the
spinning video heads, and abuse caused by rocks, toys, and peanut butter and
jelly sandwiches.

  2.2) VCR repair

Note: for VCR emergencies that just cannot wait, the solution may be found
in the document: "VCR First Aid" and you may not need to read further.  "VCR
First Aid" deals with the half dozen or so acute problems that may tempt you
to throw something through the window - or worse.

Even if you are a technoklutz who lets your kids change the light bulbs in your
house and would never consider tackling any actual repair or internal
maintenance of your VCR, some basic awareness of the principles of video
recording and the likely causes for common problems will enable you to
intelligently deal with the service technician.  You will be more likely to
be able to recognize if you are being taken for a ride by a dishonest or just
plain incompetent repair center.  For example, did you know that one of the
most dreaded of problems - the tape eating VCR - can often be remedied by
a thorough cleaning and a 50 cent rubber tire?

This document will provide you with the knowledge to deal with over 85% of the
problems you are likely to encounter with your VCRs.  It will enable you to
diagnose problems and in most cases, correct them as well.  First and foremost
are the techniques for cleaning of the tape path and replacement of rubber
parts like belts, tires, and the pinch roller - the solution to many common
problems with VCRs.  With minor exceptions, specific manufacturers and models
will not be covered as there are so many variations that such a treatment would
require a huge and very detailed text.  Rather, the most common problems
will be addressed and enough basic principles of operation will be provided
to enable you to narrow the problem down and likely determine a course of
action for repair.  In many cases, you will be able to do what is required
for a fraction of the cost that would be charged by a repair center.

Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair.  It will also be easier to do
further research using a repair text such as the ones listed at the end of
this document.  In any case, you will have the satisfaction of knowing you
did as much as you could before taking it in for professional repair.
With your new-found knowledge, you will have the upper hand and will not
easily be snowed by a dishonest or incompetent technician.

  2.3) Repair or replace

While VCRs with new convenience features are constantly introduced, the
basic function of playing a tape has not changed significantly in 20 years.
Even the introduction of HQ about 10 years ago does not represent a dramatic
improvement.  Therefore, unless you really do need a quick start transport,
a real-time counter, index search, or the like, repair may not be a bad
idea.  The older VCRs are built much more solidly than the $150 models of
today.  Even high end VCRs may be built around a poorly designed transport
and flimsy chassis.  Many older VCRs - for example 10 year old Panasonic
models (and their clones) can be kept functional - nearly indefinitely,
it would seem - at minimal cost.

If you need to send or take the VCR to a service center, the repair
could easily exceed half the cost of a new VCR.  Service centers
may charge up to $50 or more for providing an initial estimate of repair
costs but this will usually be credited toward the total cost of the repair
(of course, they may just jack this up to compensate for their bench time).

If you can do the repairs yourself, the equation changes dramatically as
your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free.  The educational aspects may also be
appealing.  You will learn a lot in the process.  Thus, it may make sense
to repair that old clunker so the kids will have their own VCR or you will
have a convenient means of copying tapes (legally, of course).

BTW, if you ARE one of those individuals (and there are bucket loads) who
doesn't bother (or doesn't know how) to set the clock on your VCR, there is a
solution - at least the next time you need to purchase a new VCR.  These
machines search for a TV station that includes the time code in its
transmission format (it is in the vertical blanking interval should you care)
and automagically sets the VCR's clock from that information.  There - no
more flashing 12:00!  Many VCRs have this feature nowadays.

Chapter 3) Video Recording Technology

  3.1) Helical scan video recording

Modern VCRs - both consumer and professional - are based on what is known
as helical scan recording.  The main technological challenge that confronted
the designers of early video recording machines was achieving the necessary
bandwidth - several MHz - to faithfully capture the high frequency video
signal.  The first such machines ran normal audio tape past stationary
recording heads at high speed - 10s of feet per second - in an attempt
to solve this problem.  Needless to say, the mechanisms were complex,
a finite length of tape could only record a few minutes of video, and the
heads wore out almost as quickly.  If anything - anything at all - went
wrong with the tape transport, you were up to your eyeballs is spilled
tape.  An alternative technology was clearly needed.

Prior to practical video tape recording, the only way to preserve a TV
show was to use special equipment that essentially made a film of it off of a
video monitor.  The quality of such recordings was not very good, editing
was difficult, the film needed to be developed so playback was not
immediate, and of course, the film could not be erased and reused.

The first successful commercial video tape recorder was introduced around 1956
with the Ampex Quadplex - a $50,000 machine using 2 inch open reel tape and
a high speed spinning head with 4 pickups rotating across the tape.  This event
revolutionized commercial broadcasting.  However, this technology was much too
complex, cumbersome, and expensive for consumer use and has a number of
technological disadvantages as well.

For a consumer video tape recorder to be successful it was felt that the
following three major hurdles had to be overcome:

* Tape loading had to be simple and foolproof using a cassette - none of
  this open reel stuff.

* A cassette had to hold at least an hour of color video.

* The cost to the consumer had to be less than $1000 (1970's dollars!)
  for the machine and perhaps $20 per hour for the tape.

The rotating heads of the Quadplex machine provided the needed
tape-head speed to achieve sufficient video bandwidth.  However, the transport
was much too complex for a consumer machine.  Another disadvantage
was that since a video frame consists of many adjacent tracks on the
tape (16), special effects like stop motion as well as forward and reverse
search were not possible without a frame store.  While this would not be
out of the question today, the cost of such a device in the 1950's would
necessitate the consumer taking out a second mortgage to pay for it.
Finally, the 2 inch wide format required too much tape for achieving
a cost effective 1 hour program time and made the design of a manageable
cassette an impossibility.  A separate room would be needed to house a
modest size video tape library!

Helical scan overcomes most of these problems.  Rather than scanning
across the tape, the tape is wrapped a bit over 180 degrees around a rotating
drum at a slight angle.  Thus, successive tracks are written diagonally
across the tape and can thus be much longer than the width of the tape
as in the Quadplex.  The tape, therefore can be rather narrow.  The first
helical scan tapes used a 1 inch format but narrower tape soon followed.
The most common formats today are forms of VHS (and BETA) at 1/2", and 8 mm
(mostly used for portable applications in camcorders and data storage.)
4 mm tape is used for high quality audio (DAT) as well as data storage.

  3.2) VHS video

Most of the following discussion unless otherwise noted applies to the VHS
format.  Beta, which preceded VHS into the marketplace and which has all
but disappeared for consumer VCRs is actually a somewhat better system
technologically with superior picture quality.  However, Sony's licensing
practices with respect to BETA made it inevitable that VHS would triumph
in the marketplace.  Too bad in some ways.

Each track corresponds to 1 field of the interlaced video format.  Generally,
two heads opposite each other on the rotating head drum are used.
One rotation of the drum corresponds to a complete video frame with heads
designated A and B for the even and odd fields respectively.  What this
also provides is the ability to easily implement a variety of special
effects including freeze frame, and fully variable speed forward and
reverse motion with a recognizable and in many cases, quite clear picture.
With relatively minor restriction, this becomes as simple as moving the
tape forward or backward or keeping it stationary.

For a not too terrible ASCII diagram and additional discussion, also see the
section: "VHS physical tape format".

(Camcorders and other compact systems may use  2 pairs of identical heads
where the opposing pairs are separated by 270 instead of 180 degrees.  This
permits the use of a smaller, lighter video drum.)

The A and B heads are not identical either.  Their azimuth angle differs
being +6 degrees for one and -6 degrees for the other.  This is one of
several techniques used to minimize crosstalk between adjacent tracks.
Azimuth angle is how far the head gap is from being perfectly perpendicular
to the direction of tape-tape motion.  For example, a head with an azimith such
as / will ignore most of the information recorded with an azimith of \.

Note that the head gap - the distance between pole pieces - is on the order
of 1 um - 1/25,000 of an inch.  As a point of reference, a human red blood
cell is about 7 um in diameter and an average sheet of typing paper is
about 100 um in thickness.  The gap is filled with a nonmagnetic material
to prevent it from getting clogged and to force the magnetic flux out
of the head structure and into the tape magnetic coating.  This remarkably
fine spacing is necessary to achieve the multimegahertz video bandwidth.

Actual tape motion for a VCR is remarkably slow.  To someone familiar with
audio decks, the tape in a VCR even at SP speed (the fastest) seems to
be crawling along.  Their first reaction is often one of: "there must be
something wrong as the tape is moving sooo slooowly."  Nope, just amazing
technology.  The SP speed of a VHS VCR corresponds to a linear
tape speed of only 1-5/16 ips - slower than for an audio cassette deck
(1-7/8" ips).  EP speed is 1/3 of this - 7/16 ips.  However, the effective
tape speed as seen by the video heads is over 15 feet per second due to the
spinning video head drum.

The luminance (Y) and color (C) components of the composite video signal are
recorded differently.  Luminance, which is in effect the black and white
picture with all the high resolution components but no color, is
frequency modulated on a carrier at around 3.4 MHz.  The deviation is
about 1 Mhz and the maximum frequency recorded on a VHS tape is a little
over 5 Mhz (BETA is slightly different and S versions of BETA and VHS
extend some of these to achieve higher bandwidths.  The color signal
is separated from the composite video and is amplitude modulated on
a 629 KHz carrier.  This is called the color under' system.  The 'U'
in U-Matic, a very popular industrial VCR 3/4" format (which predates
Beta and VHS and is still in use) stands for this.

  3.3) VHS audio

Sound for the VHS format is not merged into the video signal on the tape.
For non-HiFi VHS VCRs, a separate stationary tape head is responsible for
the audio signal.  Due to the very slow tape speed, audio quality is not
even comparable to a cheap audio cassette player even at the SP speed.  VHS
HiFi overcomes this by FM recording of the audio signal deep in the tape
(recorded by a separate set of HiFi heads just before the video information),
actually buried under the video information.  The left and right audio
channels are recorded in separate frequency bands - centered around 1.3 and
1.7 Mhz respectively.  The azimuth angles for the HiFi audio heads are +/- 30
degrees which minimizes crosstalk between the recorded HiFi audio and video

Since the head-tape speed for the VHS audio track is the same high rate as
for the video track and exceeds that of a typical audio cassette deck by a
factor of more than 100, VHS HiFi audio reproduction - frequency response,
signal to noise ratio, and dynamic range - is excellent and approaches
that of a CD.  In fact, using a T120 video cassette in EP (SLP, 6 hour)
mode simply to record stereo music (with the video ignored or blanked)
is extremely cost effective.  What other media/technology will store a 6 hour
concert with nearly perfect reproduction for under $2?  (Note: if you do
this, some VCRs will require some kind of video input to maintain stable
tape speed.  You can just ignore the video portion on audio playback.)

There are two disadvantages to VHS HiFi, however: (1) there may be some
degradation of video quality due to unavoidable interactions with the buried
audio, and (2) it is not possible to rerecord (dub) only the audio without
disturbing the video.

  3.4) VCR servo systems

Linear tape motion and head drum rotation must be precisely synchronized
during record, play, and special effects play modes.  The general functioning
is similar for all but the source of the basic reference signal differs for
play and record.  Some of the specific relationships may differ depending
on the specific VCR design.

Record: reference signal is vertical sync pulse from video input:

* Head drum rotation is phase locked to vertical sync pulse so that
  appropriate head (of the A-B pair) is in contact with the tape
  during the appropriate video field.

* The speed of the capstan which moves the tape through the transport is
  also locked to the vertical sync pulses so that the selected linear
  tape speed (SP, LP, EP) is maintained.

* Control pulses (30 Hz for US NTSC) are recorded along the bottom edge
  of the tape by a stationary control head.

Play: reference signal is timing pulse derived from quartz oscillator:

* Capstan rotation speed is locked to a 30 Hz pulse derived from
  a precise quartz crystal oscillator.  Head drum rotation is phase
  locked to the control pulses now being read off of the tape by
  the Control head.

* The tracking control is used to adjust the relative phase of the
  head drum with respect to the control pulses.  This permits the
  head path across the tape to be aligned with the actual recorded tracks.

  3.5) Video Special effects

For CUE (fast play forward) and REV (fast play reverse), the capstan speed
is phase locked to a multiple of the control track.  Since the video heads
are crossing multiple tracks during these modes, some noise bars are
unavoidable.  At SP speed, special wide or dual azimith heads are required
to minimize this degradation.  Thus, only 4 head VCRs can play SP tapes at
fast speeds with minimal noise.  With EP speed, the tracks actually overlap
and a normal video head is wide enough to pick up enough signal from adjacent
tracks to produce a mostly noise free picture.  Due to the way adjacent tracks
line up with LP speed, most of these special effects cannot be used 
due to serious tearing of the picture.  The sophisticated processing
needed for proper support at LP speed is generally not included in modern VCRs
due to the apparent lack of interest in the LP speed (recording support at LP
speed seems to be absent in more and more newer VCRs though they will all
play back LP tapes at normal playback speed).

Really slow speed is usually implemented as a variable frame advance with
the tape fully stopping between frames.  Special sets of video heads provide
the best quality.  Freeze frame (PAUSE) uses the same set of heads.  As with
CUE and REV, acceptable picture quality is provided even with a 2-head VCR
for EP speed recorded tapes.  In all cases, picture quality can be further
improved through the use of a digital frame store.

Note that the servo systems in consumer VCRs are rarely precise enough to
implement the kind of instantaneous forward or reverse frame advance that
is present in high performance (and high cost) editing decks having jog
shuttle knobs with instantaneous and precise response. 

  3.6) For more information on VCR technology

The books listed in the section: "Popular books on VCR maintenance and repair" include additional information on the theory and implementation of
the technology of video recording and VCRs.

For some information on helical scan audio and data recording, see: Sprague's
Technical Library.

  3.7) On-line tech-tips databases

A number of organizations have compiled databases covering thousands of common
problems with VCRs, TVs, computer monitors, and other electronics equipment.
Most charge for their information but a few, accessible via the Internet, are
either free or have a very minimal monthly or per-case fee.  In other cases, a
limited but still useful subset of the for-fee database is freely available.

A tech-tips database is a collection of problems and solutions accumulated by
the organization providing the information or other sources based on actual
repair experiences and case histories.  Since the identical failures often
occur at some point in a large percentage of a given model or product line,
checking out a tech-tips database may quickly identify your problem and

In that case, you can greatly simplify your troubleshooting or at least
confirm a diagnosis before ordering parts.  My only reservation with respect
to tech-tips databases in general - this has nothing to do with any one in
particular - is that symptoms can sometimes be deceiving and a solution that
works in one instance may not apply to your specific problem.  Therefore,
an understanding of the hows and whys of the equipment along with some good
old fashioned testing is highly desirable to minimize the risk of replacing
parts that turn out not to be bad.

The other disadvantage - at least from one point of view - is that you do not
learn much by just following a procedure developed by others.  There is no
explanation of how the original diagnosis was determined or what may have
caused the failure in the first place.  Nor is there likely to be any list
of other components that may have been affected by overstress and may fail
in the future.  Replacing Q701 and C725 may get your equipment going again
but this will not help you to repair a different model in the future.

Having said that, here are two tech-tips sites for computer monitors, TVs,
and VCRs:

* http://www.anatekcorp.com/techforum.htm            (currently free).
* http://www.repairworld.com/                        ($8/month).
* http://ramiga.rnet.cgl.com/electronics/info.html   (free large text files).

These types of sites seem to come and go so it is worth checking them out from
time-to-time even if you don't have a pressing need.  If possible, download
and archive any useful information for use on a rainy day in the future.

Chapter 4) VCR Placement, Preventive Maintenance, and Rental Tapes

  4.1) General VCR placement considerations

Proper care of a VCR does not require much.  Following the recommendations
below will assure long life and minimize repairs.

* Allow adequate ventilation - VCRs are not huge users of power but there
  is some heat buildup nonetheless.  Leave at least 1-1.5 inches around
  all sides and top for air circulation.  Try not to place the VCR near heat
  producing equipment.

* Do not put anything on top of the VCR that might block the ventilation
  grill.  To be safe, don't put anything on top - period.  Tapes are
  especially bad - for the tapes - as the heat and possible magnetic
  fields in the vicinity will tend to age them prematurely.

  In addition, modern VCRs are NOT built like the Brooklyn Bridge!  The
  weight of a TV or stereo components could affect the VCR mechanically,
  messing up tape path alignment or worse.

* If possible, locate the VCR away from the TV.  Some VCRs are particularly
  sensitive to interference from the TV's circuitry and while this won't
  usually damage anything, it may make for less than optimal performance.

* Don't locate VCRs in dusty areas if possible.  Consider the use of a dust
  cover when not actually being used if you have no choice of location.

* Don't locate VCRs in areas of high (tobacco) smoke or cooking grease vapors.
  I cannot force you to quit smoking, but it is amazing how much disgusting
  difficult to remove brown grime is deposited on sensitive electronic
  equipment in short order from this habit.

* Make sure all input-output video and audio connections are tight and
  secure to minimize intermittent or noisy pictures and sound.

* Finally, store video cassettes well away from all electronic equipment
  including and especially loudspeakers.  Heat and magnetic fields will
  rapidly turn your priceless video collection into so much trash.
  It is also recommended that you store the cassettes on edge so that the
  tape edges are not subject to pressing against the case and that you
  run them through a VCR or winder/rewinder from start to end and back
  on FF/REW at least once a year (another pair of recommendations that
  are rarely followed).

  4.2) Video tape quality

"What are the 'good' and 'bad' brands of videotapes (T-120)?  Are the 'extra'
 or "high" grades really better?"

I would avoid brands you never heard of.  K-mart brand, Recoton(sp), the street
vendor from whom you buy Chinese food, whatever.

Higher grade tapes are not necessarily worth the expense but in my experience
with some like Maxell and Scotch, going one level up from the cheapest is
worthwhile and results in a noticeably better picture.

Only a few companies actually manufacture the raw tape stock.  For what it's
worth (FWIW), I usually use Scotch, under $2 for a T120 - usually in a 3 pack
for $5 or $6 with one higher grade cassette.

The higher grade tapes may actually be harder on the video heads due to
their formulation but this probably doesn't matter for the ordinary user..
You don't need HiFi grade tapes for HiFi - any tape will work.  However,
higher grade tapes may last longer with higher quality results in demanding
situations like 24 hour a say security monitoring.

Consumer Reports does a review every so often, check back issues.  I believe 
their conclusions were generally to buy name brands by price.  Whether you
believe in Consumer Reports or not, checking their ratings at least gives
you an additional data point.

  4.3) How long do video tapes last?

(From: Raymond Carlsen (rrcc@u.washington.edu)).

I have not seen any "official" guidelines on tape longevity for a long time,
since the Beta days.  Use of old tapes will not generally ruin video heads but
may clog them.  Proper manual cleaning restores normal operation.

Your mileage really depends on several factors, the most important being the
conditions under which it's used. I've seen VCRs that can chew up a tape in
one or two passes and make it unusable. High humidity and heat will cause
tapes to stick to the head drum and wear prematurely. Shuttling tapes back and
forth and leaving them sit in pause (on one spot) can accelerate wear.

Under ideal conditions: clean machine in good alignment running a tape from
beginning to end without stopping is as good as you're going to get. Alignment
tape manufacturers used to indicate expected life as the "number of passes".
No significant degradation in 50 passes, but after that, dropouts become
obvious. Maximum life is 200 passes. At that point, the tape is starting to
break down with oxide particles being shed onto the heads (actually happens
with all tapes to some degree) causing head clogging. With tapes of any age, a
liquid spill such as soda pop ends the game right there. It can be cleaned,
but unless it's your precious home movies, forget it.
I would use a tape until the dropouts become annoying. Dropouts are places on
the tape where the oxide is missing. You'll see them more at the beginning of
a tape where it's mechanically stressed by loading and unloading. A lateral
scratch on a tape (caused by buildup of gunk in a VCR) will show up as a 3 or
4 line continuous dropout somewhere on the screen.  Look at some heavily used
rental tapes and you'll get the idea. So, bottom line: use it until it shows
it's age. :)

  4.4) Preventive maintenance

You no doubt have heard that a VCR should be cleaned and checked periodically.
This is basically good advice but few people actually do follow it.  I cannot
give a specific schedule to follow as many factors influence the amount of
wear and tear on your VCR:

* If you mostly use new brand-name tapes to make your own recordings,
  rarely play rental tapes, and have the VCR located in a clean cool relatively
  dust free and smoke free location, you may be able to go 5 years with
  no problems.  However, a more prudent interval would be 1-2 years
  between preventive maintenance and rubber replacement after 4-5 years.
  Obviously, if you time shift every evening or have frequent marathon
  viewing parties you should probably reduce the PM interval.

* If you play rental movies every weekend or older tapes and have chain smokers
  in the house, every 3 months may not be frequent enough.  I would suggest
  6 months to 1 year between preventive maintenance and rubber replacement
  after 3-4 years.

If you want some guidelines, see the next section: "Sample VCR preventive maintenance schedule".

Realistically, you are not going to do any PM anyway.  So, just be aware
of the types of symptoms that would be indications of the need for cleaning
or other preventive or corrective maintenance - erratic loading, need
to convince the VCR to perform certain operations, whirring motors without
completing cycle, VCR taking longer to go into or out of a particular mode
than you recall, jittery or noisy picture, or wavering or muddy sound.
If your inspection reveals deteriorated rubber parts, obviously these
should be replaced regardless of their age.

Of course, acute symptoms like a tape jam or tape munching episode is a
sign of the need for emergency treatment.  This still may mean that a
thorough cleaning is all that is needed.

I generally don't consider cleaning tapes to be of much value for
preventive maintenance since they do not run long enough or with enough
force to clean the rollers, stationary heads, and guide posts.  Also,
the dry type, in particular, are abrasive and frequent use may cause
premature wear to the expensive video heads.

The following are some reasons to inspect and clean a VCR periodically:

* This will maintain performance at factory new levels.  Dirt, dust,
  and shed tape oxide all contribute to a reduction in stable tape
  movement and possible problems with noisy or jumping pictures and
  muddy or wavering sound.

* Dirt, dust, and other crud can be deposited on the tapes you run through
  the VCR contaminating them and passing problems on to this or other
  VCRs in the future.

* Your inspection will reveal if service parts like belts, tires, the
  pinch roller, etc. are in good conditions so that future surprises
  will be minimized.

If you follow the instructions in the section: "General guide to VCR cleaning and rubber parts replacement", there is minimal risk to the VCR.  However,
don't go overboard.  If the belts are in good condition (by appearance and
stretch test), just clean them or leave them alone.  This is especially true in
the (generally infrequent) designs of some models of VCR tape transports where
significant disassembly is required to replace a belt.  In this situation,
you risk not being able to put everything back the way it was.  Most belts can
be replaced with little or no disassembly beyond removing the top and
bottom covers and possibly any circuit boards that may be in the way,
Sometimes one or two additional screws will need to be loosened or removed
to move a bracket or shield.

  4.5) Sample VCR preventive maintenance schedule

Here is an example of the recommended inspection, lubrication, and
replacement schedule for a typical VCR as provided by the manufacturer.
This is from the Sams VCRfact for a particular non-HiFi RCA VCR.  I am
providing this for information only and am not necessarily recommending
these or other similar hard and fast rules for VCR preventive maintenance.

It is not clear here what a 'tape' is though the comments that go along with
this table seem to indicate that it means a T120.  However, parts that deal
with tape loading are affected not by how long a tape is played but by the
number of loading cycles.  Wear on the video heads, on the other hand is
strictly a function of play/record time.  Wear of the A/C and erase heads
depends on both time and tape speed.  Thus, these are additional reasons
not to take the numbers below too literally.

  After         What to do                      Which parts
250 tapes         Clean          A/C head, capstan, erase head, pinch roller,
                                  impedance roller, supply reel table, takeup
                                  reel table, video heads.

500 tapes        Replace         Video heads (upper cylinder).

750 tapes        Replace         Pinch roller

1000 tapes       Grease          Loading cam gears, impedance roller shaft,
                                  roller guide tracks.

                   Oil           Supply reel shaft, takeup reel shaft.

                 Replace         Reel belt, loading motor belt, main brake
                                  spring, main brake arms (left and right).

2000 tapes       Replace         A/C head, erase head, supply reel table,
                                  takeup reel table.

2500 tapes       Replace         Cylinder unit.

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