Common Problems

Playback problems
	Automatic shut off	Explanation of tape end sensors
	To reduce problems with playing and (re)winding	Description for winding tapes and cassettes
	No tape transport	Frequent problems with tape transport and consequences
	Condition of tape	Description of various conditions
	Repair of video tapes	Description of damages to tape and what to do
	Professional audio recording with video recorders	How to differentiate between audio and video tapes
Video file about errors
	Video about errors	A video made by Phonogrammarchiv Vienna

Automatic shut off / tape end sensors

Video recorders have end-of-tape detectors to make sure the machine is automatically switched off when the end of the tape is reached. Problems with this detection system occur frequently, causing the machine to refuse to play the tape or to stop playing for no apparent reason. When this happens, it is therefore advisable to check if the video tape is damaged or if the end-of-tape detection mechanism is faulty.

open reel tape
cassette
cartridgesystemen

Open reel (reel to reel) systems
With open reel tape there are two common systems for end-of-tape detection:

1. The tape passes between a small lamp or infrared light and a photo cell. As soon as the end of the tape is reached, the photo cell receives a light pulse that switches off the motor drives. When the tape is spooled back the same happens at the beginning of the tape.

2. The tape moves along a thin vertical guide. The guide moves horizontally against a micro switch and presses the switch to the on position while the tape is running, so that the motor drives are turned on. When the tape reaches the end and slips from the spool, the guide is released and removes pressure from the micro switch, switching it off so the motor drives stop. When spooling back the same happens at the beginning of the tape.


Cassette system

Within the plastic cover of the cassette the tape is wound onto one of the two spools. On each end of the tape a transparent leader is fixed to the spools. The tape moves between a lamp or infrared light and a photocell, which detects when the transparent leader is reached, causing the motor drives to switch off.

Note: With the U-Matic and Akai VK cassette systems the supply spool is on the right side of the cassette and the tape runs from the right to the take-up spool on the left. With most other systems (VHS, Betamax, MII, Betacam etc) the supply spool is the left one and the take-up spool is on the right.

Note: On some recorders a switch can be used to instruct the machine to stop and wind back the tape at a particular point or to replay in a loop. Make sure that in playback this switch is off (‘memory off’) to prevent the tape stopping unexpectedly.

Cartridge system

Cartridges differ from cassettes in that only a supply spool is present in the plastic cover: the take-up spool is part of the machine. At the beginning of the tape there is a piece of sturdy transparent leader. When the cartridge is inserted into the machine the leader winds from the cartridge and is guided through the recorder to the take-up spool.
The cartridge system has the advantage that the tape must always be rewound completely before it can be removed from the machine. This prevents tape damage by being taken out when loaded in the machine.

As with the other systems, end-of-tape detection depends on a lamp or infrared light and a photo cell.

Note: The recorder may also have a timer to program it to instruct the machine to stop at a specific moment and wind back the tape at a particular point or to replay in a loop.
On playback make sure the clock is set to maximum (turned completely to the right) to avoid the tape stopping and starts rewind unexpectedly



top

To reduce problems with playing and (re)winding

At the end of the programme, let the tape continue to run for at least a minute, then
stop and wind back to the original spool.

If you prefer to let the tape run out till the end, make sure that before storing the tape in its box the spool is labelled ‘tail out’. Bear in mind that you have to check the labels after every periodical rewinding of the tapes (every six months or every year). In all cases when tape is moved from the original spool to another, the data on the label of the original spool should be copied to the new one.

To reduce static and/or sticking caused by playback or copying, always wind a tape or cassette forward to the end of the tape and then rewind to the beginning.

With open reel tapes always take care the tape is wounded evenly and flat.

Never remove a tape from the machine if it has not been (re)wound completely, as a half run tape is more prone to damage.

1- and 2-inch tape will not be discussed here any further. If you to have 1- or 2-inch. professional formats they should only be processed by professionals. It is recommended that you consult a professional video company, an expert in video preservation or a broadcast company as they know how to deal with these materials.



top

No tape transport

Tape transport problems with U-matic cassettes

Transparent areas
Error message on display
Sticky tape

Transparent areas
A ‘hole’ in the binder layer and/or backcoating

Many devices have end-of-tape detectors that cause the machine to switch off when a transparent leader at the end (or beginning) of the tape is reached. When a tape is damaged, for instance because it got stuck in the machine, this may result in small transparent areas on the tape where the back coating or the magnetic layer is scratched. If that piece of tape comes across the end-of-tape detectors, it may (incorrectly) be taken for the transparent end-leader, and consequently the machine will stop in the middle of the tape.


A ‘hole’ in the binder layer and/or backcoating

If you suspect tape damage may be causing such problems, remove the cassette from the machine with the tape at the place where it was stopped. Open the tape cover of the cassette by pushing the slider in the groove next to the tape cover and place a felt-tip pen between the open tape cover and the cassette house, so that it stays open.

Open the tape cover, place a felt-tip pen in between the cover and the cassette

Use lintfree cotton gloves and put a finger under the tape to pull it out a little bit. You should be able to see quite easily where the tape is damaged. Tape that is crinkled can be straightened to some extent by pulling it along an aluminium strip.

Note: make sure you pull the back of the tape along the aluminium strip, not the side with the magnetic layer.


crinkled tape and an aluminium strip

If there is a ‘hole’ in the magnetic layer or the back coating, that causes the machine to stop, you can use a thick, black felt-tip pen to darken the damaged area at the back of the tape, never on the side of the magnetic layer. Leave to dry and repeat if necessary. When the tape is completely dry, wind it back into the cassette by turning one of the spools from below and close the tape cover.

If the tape is seriously damaged, it may be necessary to remove the damaged stretch of tape. Cutting out a piece of tape, however, will cause the image to jump when it is played back (see repairing video tape).

Error message on display
(How to manually take out a cassette)

Most U-matic cassette recorders have a display for timing and error information.
When a cassette is in the machine and stops unexpectedly there will be an error code in the display. Look in the manual for an explanation of the error code or try the following procedure:

If you need to remove the cassette while the machine is blocked, switch off the power supply and open the cover of the machine. If the tape is still correctly threaded around the video drum or not threaded at all, switch on the power while you press the EJECT button repeatedly until the threading mechanism is turned on. In most cases the tape will unthread completely, and the cassette will come out.

If this does not work, or if the tape is in a loop, you will need to remove the cassette manually. Keep the power switched off and use lintfree cotton gloves to remove the tape very carefully from the transport mechanism. Put a sheet of A4 paper over the threading mechanism and place the loops of tape on this sheet.

To the side of the cassette loader you will see the little loading motor. Gently turn the gear until the cassette loader rises up. When the cassette has come up completely, remove it carefully from the machine together with the looped tape. Make sure the cassettes tape cover is kept open- if necessary block it with a felt-tip pen. When the cassette is out of the machine wind up the loose tape by turning one of the spools from below.

Note: it is essential to keep the tape cover of the cassette open: it will damage the tape if it closes while you are still removing the cassette from the machine. When the cassette has been safely removed, you can let the tape cover shut. If necessary, use a pencil to push down the slider in the groove next to the tape cover.

In the same way you can open the tape cover if you need to repair the tape. Place a felt-tip pen between the tape cover and the cassette to block it (see also Repairing tape).

Sticky tape
There may be different reasons why magnetic tape starts to stick in the machine during tape transport. It may be a matter of static electricity that causes the tape to stick to the guides or the head drum, but a chemical reaction of the back coating is another possible explanation. Spooling the tape to the very end and back again to the beginning will reduce electric charges considerably and may solve the problem.

If the cause is from chemical deterioration of the back coating layer, the tape will have to be passed a few times through a tape cleaning machine. If this does not help, a professional in video preservation should be consulted (http://www.sony-europe.com/restoration). There are more ways to reduce tapes sticking, even in difficult cases, but these measures should be left to the specialist.



top

Condition of tape

Uneven winding
Mould
Damage

Uneven winding
A tape may show uneven winding, with wraps not lined up properly that stick out from the edge of the tape. Irregularities of the tape winding are often an indication of improper handling or storage, or a problem with the machine on which the tape was last played. Winding the tape to the end and rewinding it again on a properly adjusted machine may reduce the problem. Irregular tape winding causes the tape to run less smoothly and increases the risk of damage.

Mould
Tapes that have been stored under sub optimal conditions can show signs of mould or fungi. White stains on the tape are an indication of this. Clean the tape a couple of times in a professional tape cleaning machine from RTI (http://rtico.com/products1.html), or consult a video preservation specialist.

Damage
A tape may be crumpled or damaged when it gets stuck in a machine. Tape that is wrinkled can be straightened to some extent by pulling it (with a little force) along an aluminium strip.

Note: make sure you pull the back of the tape along the aluminium strip, not the magnetic layer. If the tape is seriously damaged, it may be necessary to remove the damaged piece, so that the tape can still be played. When a piece of tape is cut out, however, the image will jump when it is played back as parts of image lines are cut off.



top

Repairing video tape (not necessarily broken but seriously damaged or crumpled)

When a video tape is seriously damaged, crinkled or broken, consider (after reading the instructions below) if you can repair it yourself. It is not too difficult to repair a video tape by cutting out a damaged piece. If you have any experience with tape splicing then cut out the damaged tape and make a neat splice. Take care to attach the adhesive tape only to the back of the tape, leaving no space between the two tape ends. Use only special polyester splicing tape such as that used with film editing.

If you do not have any experience before you try to repairing a valuable tape, please first practise on a disposable piece of tape or visit a video restoring company.

Before splicing you need to prepare some items on a clean surface (for example a glass plate)

- thin polyester adhesive tape (for example adhesive tape used for film editing)
- scissors (preferably anti-magnetic)
- lintfree cotton or linen gloves
- something to weigh down the tape to make sure it does not move (for example a ruler)


preparations video tape repair

Place a white sheet of paper with a horizontal line under the glass plate to help line up the tape.


Reel to reel tape repair
Cut the tape with the (anti-magnetic) scissors in the middle of the damaged part. Place the two ends over each other where the damaged area has ended. Cut both ends simultaneously on a slant. Both ends will then have an identical diagonal ending.
Polyester tape does not tear so use the scissors to cut a small piece of tape (from 15mm wide tape) about 6cm long.

Stick this piece of adhesive at the back of the video tape so that half of the width of the adhesive tape (7.5 mm) is attached to one of the tape ends. Place that piece of video tape with the back down on the glass plate in line with the line on the paper. Then take the other piece of video tape, keep it in line, above the adhesive tape and fasten it carefully to the rest of the 7.5mm adhesive tape.

There should be no space between the two ends of the video tape that are stuck on the adhesive. Rub carefully with the glove on the magnetic side and then cut off the bits of adhesive that stick out on the sides of the video tape.

Make sure no fragments of adhesive tape are left. You may cut the sides of the tape in a subtle wave form, going inwards to the tape, so that at the splice the tape becomes narrower by 1mm. at the most. Rewind the video tape completely and, if possible, clean the tape in a cleaning machine.

U-matic cassette tape repairing
Open the tape cover on the cassette as shown in the photograph. Place a felt-tip pen in between the cover and the cassette so that it cannot close or fasten the cover of the cassette with a piece of adhesive tape.
Free a loop of tape carefully from the cassette by pulling at both sides. Cut and paste the tape as described above, and rewind the tape by turning the spool from below. If possible clean the tape in a video tape cleaning machine.

Open the tape cover, place a felt-tip pen in between the cover and the cassette


U-matic cassette crinkled tape


pasting the tape


end result

Note: With VHS cassettes, you can release the tape spools by pushing a pencil in the hole at the bottom of the cassette, between the two spools. Keep it there while pulling a loop out of the cassette. Cut and paste the tape as described above, and rewind the tape by turning the spool from below (while turning the spool you will hear a rattling sound).

Note: Cassette tape is always wound with the magnetic layer to the outside. Be careful not to touch the magnetic layer or make sure the adhesive tape does not stick to the magnetic layer side of the tape or it will be seriously damaged.

Also open reel tapes are wound with the emulsion layer (magnetic layer) to the inside except 1 inch B-format (BCN) which has the magnetic layer outside. The inventors of the 1 inch B-format (BCN) system chose this because for a quick recognition of the kind of video system used.



top

Audio recording on video tape

U-matic PCM
ADAT S-VHS digital

U-matic and S-VHS tapes are also used for recording digital sound. Thus, before you put a cassette in to a video machine, check the written information on the box and cassette to be sure the cassette is used for video recording.

U-matic PCM
A PCM (Pulse Code Modulator) audio converter is used to convert two analogue sound channels into a digital signal that is recorded on tape via the BNC-video input and the video heads. On an audio channel a TimeCode is generated to enable editing. With a PCM reader the sound can be reproduced (via the BCN video output).

Audio recordings for CD were edited by using a U-matic video editing set in this way in the early days of the CD music industry. Finally the edited PCM signal was burned to a glass master and was used to multiply CDs.
If a PCM cassette is accidentally played in a video machine you will see many horizontal black and white blocs with vertical lines on the screen.

ADAT S-VHS digital
Specially prepared S-VHS tape cassettes are used by the Alesis ADAT 8-track digital audio recording. These cassettes have a maximum recording time of 63 minutes. If they are accidentally played on a VHS recorder, the screen shows snowy horizontal stripes and the sound is reproduced as a quaking whistle.

Note: Always check the label on a cassette to verify what is on the tape, to make sure you are using the right equipment for the particular tape. Bear in mind you may be dealing with an audio recording.



top

Errors on videotapes

This 13 minute film (153 MB) has been prepared by the Phonogrammarchiv in Vienna and shows errors on video tape that they have regularly encountered in their work on video preservation and transfer. The errors can result from the original recording (analogue or digital) or deterioration of tape. It is important to distinguish between errors made in the original recording (that are part of the original document) and errors that are related to the condition of the tape or the machine, which in some cases can be remedied is important. For instance, it saves you spending time trying to solve a ‘playback problem’ that is in fact an error in the recording.

start the video (wmv format)

top