This application relates to improvements in video display units and especially to improvements in the external casing of video display units.

The concept of separating the display side of a system from the rest of the interface and other subsystems such as audio amplifiers, speakers, tuners and intermediate amplifiers, has led to the development of stand-alone video, display units.

Display, tubes are always surrounded by high voltage and high energy circuits required for driving the tube. It is therefore essential to achieve complete isolation of the circuits associated with the tube from the rest of the circuits associated with any other sub-system.

According to this invention & video display unit having a casing comprising a screen and an enclosure, is characterised in that the enclosure is made of metal. New technology has enabled video units to be designed with a very:.low power dissipation. In most visual display units this power dissipation may be kept to below 80W. Metal is a good radiator of heat and this low level of power can effectively be dissipated through the metal case. The greatest advantage of the system is therefore that no ventilation openings such as slots and louvres are required in the casing. This has many advantages. The metal case is a screen

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for radio frequency interference. ^' This screening however is improved so that it is almost complete,by the absence of any ventilation openings.

Since the enclosure is metal it means that it is fire proof and consequently very safe _* The whole video display unit may now be hermetically sealed which means that the display unit can be used in a dangerous environ¬ ment.

The video tube may be sealed into the enclosure by a rubber gromraets. The screen is preferably affixed to the enclosure by a rubber seal. This means that the video . display unit is waterproof. Thus in an office environment the video display unit may be used with no problems caused by any spillages of beverages or other drinks. With a conventional visual display unit, a knocked over cup can cause liquid to enter the unit and _: comeinto contact with the circuits and tube within:,

Since no ventilation holes are required in- the enclosure, the display is safe since children cannot stick either their fingers or other objects into the enclosure to electrocute themselves.

This invention makes it possible to produce equipment which is very attractive and at the same time meets standards of safety never before achieved in the domestic environment. These video display units may be television displays. Preferably they are used for the new ,generation of colour displays which are used in conjunction with a wide variety of applications such as Viewdata, Prestel, Antiope, Teledon, Unit Video, Interactive Television, Cable Television, microcomputer displays, games, education and information terminals, learning centres, advertising, point of slales terminals, industrial displays and process controls.

Any metal which is a good heat conductor may be used for the enclosure, such as, copper, silver, aluminium or zince, or zinc alloys.

With colour tubes it is preferable that the metal is

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non-ferrous to avoid the complications caused by earth magnetic fields.

.Most preferably the enclosure is aluminium since this is a very light material. Also this means that the enclosure maybe made by die casting which provides a cheap and efficient method of manufacturing the enclosures.

The thickness of the metal is preferably between 18 and 24 gauge to achieve the heat dissipation through the enclosure. The thickness is more preferably 22 gauge. The enclosure may be made ^" in any size but is preferably just bigger than one of the standard, 12", 14", 20", 22", 24", 26" tubes. If the enclosure is large enough to fit the tube inside then the surface area of the enclosure will be large enough to dissipate the heat produced by the tube and its associated circuits.

An example of a video display unit in accordance ,with this invention will now be described with reference to the accompanying drawing which is a section through the video display unit. A video display unit 1 comprises a glass screeen 2 and a metal enclosure 3. The screen 2 is a standard 20" screen. Within the enclosure 3 is situated a 20" colour tube 4. Driver circuits 5 to drive the tube 4 are also contained within the casing 3. The metal enclosure 3 is die-cast aluminium and has a thickness of 22 gauge. It is thus light and inexpensive. A rubber seal 6 seals the screen 2 to the enclosure 3. A further rubber seal 7 seals the tube 4 within the enclosure 3. The enclosure 3 is continuous with no slots, holes or other ventilation openings. All heat dissipated by the tube 4 and circuits 5 is radiated through the metal enclosure 3. Thus nothing can enter the visual display unit 1, such as liquid split, or a childs fingers,making it very safe. The control button 8 is situated below the screen 2.

A rubber grommet 9, seals the button 8 to the enclosure 3 to ensure that the cabinet 1 is completely waterproof. It is

also fireproof and provides an effective screen against radio frequency interference.

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