Abstract:
A shielding apparatus of projection television is disclosed. A metal shield casing made of metal plate members shields an optical block and a circuit block. Metal plate printed board holding sections are connected to the metal shield casing detachably at predetermined intervals, and hold the printed board. Connection sections of the metal shield casing elastically contact with the printed board holding section, and connect so as to conduct electrically with the metal shield casing. Further, a part of the metal plate casing of the printed board holding section is elastically fixed to the metal shield casing through the connection section, and shields the optical block and circuit block. Thus, the shield casing excellent in shielding effect of high frequency circuit and easy in servicing is presented.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an electromagnetic shielding apparatus of projection television including an optical block and a circuit block.  
         BACKGROUND OF THE INVENTION  
         [0002]    Hitherto, as a structure for constituting a casing of projection television, an example disclosed in Japanese Laid-open Patent No. 5-130541 has been known. In this disclosed projection television, a cathode-ray tube (CRT) and a circuit board compose a CRT block. This CRT block can be separated from the mirror, screen, and cabinet. Thus, the CRT block can be mounted easily on the cabinet.  
           [0003]    As an electromagnetic impedance countermeasure structure of electronic appliance, an example is disclosed in Japanese Laid-open Patent No. 7-183684. In the disclosed structure of shield plate, both sides of a shield plate having a conductor are fixed inside of an upper case by a pi-shaped protrusion provided inside of the upper case. Further, the shield plate, lower case, and grounding terminal of printed board of logic circuit are fastened with screw at the same position. Thus, the shield structure capable of preventing effects of static electricity or noise is obtained.  
           [0004]    Recently, as the frequency is becoming higher in integrated circuit (IC) board of circuit unit, resistance to electromagnetic impedance is further demanded in projection television and other electronic appliances. It is hence more and more needed to reinforce the shield by metal casing or the like. On the other hand, as the screw tightening portions and shielding components are increasing in number, service tends to be more and more difficult.  
           [0005]    In the case of projection television, further, even an optical clearance may cause to lower the electromagnetic shielding performance or pass undesired reflected light.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention addresses the problems discussed above, and, it is an object of the invention to present a shielding apparatus capable of realizing a shield casing for shielding the electromagnetic waves causing interference in a structure requiring only a small number of screws, and servicing easily.  
           [0007]    In a shielding apparatus of projection television of the invention containing an optical block, and a circuit block including a printed board on which an electric circuit components are mounted, a metal shield casing composed of metal plate members accommodates and shields the optical block and circuit block.  
           [0008]    A printed board holding section made of metal plate is detachable fixed to the metal shield casing at a predetermined interval, and hold the printed board.  
           [0009]    A connection section is provided in the metal shield casing so as to snap in and conduct electrically the printed board holding section.  
           [0010]    One side of the metal plate casing of the printed board holding section is fixed to contact elastically with the metal shield casing through the connection section, and shields the optical block and circuit block.  
           [0011]    More specifically, the mounting holes provided in the metal plate members positioned at the lower side of the printed board holding parts provided in the printed wiring board contact elastically with the ungula-shape-portions of the shield casing for electromagnetic interference countermeasure. Thus, the printed board holding parts electrically conduct with the shield casing to form a part of the shield casing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a conceptual perspective view of outside configuration of television receiver mounting a circuit unit of the invention.  
         [0013]    [0013]FIG. 2 is a conceptual perspective view of inside configuration of television receiver mounting a circuit unit of the invention.  
         [0014]    [0014]FIG. 3 is a side view after assembly of shield unit of the invention.  
         [0015]    [0015]FIG. 4 is a sectional view after assembly of shield unit of the invention.  
         [0016]    [0016]FIG. 5 is a sectional view when servicing the circuit unit of the invention.  
         [0017]    [0017]FIG. 6 is a sectional view when servicing the optical unit of the invention.  
         [0018]    [0018]FIG. 7 is a sectional view after assembly of terminal board unit in a prior art.  
         [0019]    [0019]FIG. 8 is a sectional view before assembly of terminal board unit in a prior art.  
         [0020]    [0020]FIG. 9 is a sectional view after assembly of terminal board unit with protrusions of the invention.  
         [0021]    [0021]FIG. 10 is a sectional view before assembly of terminal board unit with protrusions of the invention.  
         [0022]    [0022]FIG. 11 is a sectional view after assembly of terminal board unit with bends of the invention.  
         [0023]    [0023]FIG. 12 is a sectional view before assembly of terminal board unit with bends of the invention.  
         [0024]    [0024]FIG. 13 is a sectional view after assembly of terminal board unit with springs of the invention.  
         [0025]    [0025]FIG. 14 is a sectional view before assembly of terminal board unit with springs of the invention.  
         [0026]    [0026]FIG. 15 is a sectional view after assembly of terminal board unit with gaskets of the invention.  
         [0027]    [0027]FIG. 16 is a sectional view before assembly of terminal board unit with gaskets of the invention.  
         [0028]    [0028]FIG. 17 is a sectional view after assembly of cover unit with springs of the invention.  
         [0029]    [0029]FIG. 18 is a sectional view before assembly of cover unit with springs of the invention.  
         [0030]    [0030]FIG. 19 is a plane view of shield cover with springs of the invention.  
         [0031]    [0031]FIG. 20 is a side view before assembly of power source circuit unit of the invention.  
         [0032]    [0032]FIG. 21 is a side view after assembly of power source circuit unit of the invention.  
         [0033]    [0033]FIG. 22 is a sectional view after assembly of power source circuit unit of the invention.  
         [0034]    [0034]FIG. 23 is a top view after assembly of external shield component of the invention.  
         [0035]    [0035]FIG. 24 is a side view after assembly of external shield component of the invention.  
         [0036]    [0036]FIG. 25 is a rear view after assembly of external shield component of the invention.  
         [0037]    [0037]FIG. 26 is a top sectional view and detailed view after assembly of external shield component of the invention.  
         [0038]    [0038]FIG. 27 is a side view before assembly of external shield component of the invention.  
         [0039]    [0039]FIG. 28 shows undesired reflected light after assembly of projection lens and optical block in a prior art.  
         [0040]    [0040]FIG. 29 shows effective light and undesired light after assembly of projection lens and optical block in a prior art.  
         [0041]    [0041]FIG. 30 is a top view of projection lens shield and light shielding screen of the invention.  
         [0042]    [0042]FIG. 31 is a side sectional view of projection lens shield and light shielding screen of the invention.  
         [0043]    [0043]FIG. 32 is a bottom view of projection lens shield and light shielding screen of the invention.  
         [0044]    [0044]FIG. 33 is a side sectional view after assembly of projection lens shield of the invention.  
         [0045]    [0045]FIG. 34 is a side sectional view after assembly of projection lens shield of the invention.  
         [0046]    [0046]FIG. 35 is a side sectional view after assembly of projection lens shield of the invention.  
         [0047]    [0047]FIG. 36 shows undesired radiation after assembly of projection lens and optical block in a prior art.  
         [0048]    [0048]FIG. 37 is a side sectional view of projection lens shield and conductive spring of the invention.  
         [0049]    [0049]FIG. 38 is a bottom view of projection lens shield and conductive spring of the invention.  
         [0050]    [0050]FIG. 39 is a side sectional view after assembly of projection lens shield of the invention.  
         [0051]    [0051]FIG. 40 is a side sectional view before assembly of projection lens shield of the invention.  
         [0052]    [0052]FIG. 41 is a side sectional view of projection lens shield and conductive spring of the invention.  
         [0053]    [0053]FIG. 42 is a bottom view of projection lens shield and conductive spring of the invention.  
         [0054]    [0054]FIG. 43 is a side sectional view after assembly of projection lens shield of the invention.  
         [0055]    [0055]FIG. 44 is a side sectional view before assembly of projection lens shield of the invention.  
         [0056]    [0056]FIG. 45 is a side sectional view of projection lens shield and conductive gasket of the invention.  
         [0057]    [0057]FIG. 46 is a bottom view of projection lens shield and conductive gasket of the invention.  
         [0058]    [0058]FIG. 47 is a side sectional view after assembly of projection lens shield of the invention.  
         [0059]    [0059]FIG. 48 is a side sectional view before assembly of projection lens shield of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0060]    Preferred embodiments of the invention are described below while referring to FIG. 1 through FIG. 48.  
         [0061]    (Embodiment 1)  
         [0062]    [0062]FIG. 1 is a conceptual perspective view of outline of projection television receiver mounting a shield unit and a circuit unit of the invention.  
         [0063]    [0063]FIG. 2 is a conceptual perspective view of inside configuration of television receiver mounting a shield unit and a circuit unit of the invention.  
         [0064]    [0064]FIG. 3 is a side view after assembly of shield unit in an embodiment of the invention.  
         [0065]    [0065]FIG. 4 is a sectional view after assembly of shield unit in the embodiment of the invention.  
         [0066]    In FIG. 1, this projection television receiver mainly includes a cabinet  1 , a base block  6 , a speaker panel  5 , a terminal panel  4 , a speaker panel  5 , a screen  3 , and a back cover  2 .  
         [0067]    [0067]FIG. 2 shows constituent elements contained in the base block  6 . An optical block  11  includes a projection lens  9 , a projection lens shield  10 , a lamp cover  7 , and a lamp shield plate  8 .  
         [0068]    The optical block  11 , a base metal bracket  12 , a shield plate (left)  13 , a shield plate (right)  14 , a chassis metal bracket  22 , and a shield plate (rear)  23  compose the shield unit.  
         [0069]    The circuit unit is disposed in the shield unit, and a front terminal metal bracket  19  is attached to a front terminal board  19 .  
         [0070]    Herein, the circuit unit includes a power source shield  17  including a fan  16 , a power source board  18 , a signal board  20 , and the front terminal board  19 .  
         [0071]    [0071]FIG. 3 shows the configuration of the shield unit and cabinet  1 , back cover  2 , screen  3 , and speaker panel  5 .  
         [0072]    Referring to FIG. 4, the structure of the shield unit is explained.  
         [0073]    The base metal bracket  12  supports the optical block  11 . The base metal bracket  12  includes plural ungula-shape-portions  12   a.  The shield plate (right)  14  includes plural ungula-shape-portions  14   a.  Screws  15  connect the signal board  20  to the chassis metal bracket  22  mechanically and electrically. The chassis metal bracket  22  includes a fixing notch  22   a  and a fixing hole  22   b.    
         [0074]    The ungula-shape-portion  12   a  of the base metal bracket  12  is inserted into the fixing notch  22   a  of the chassis metal bracket  22 . The ungula-shape-portion  14   a  of the shield plate (right)  14  is inserted into the fixing hole  22   b  of the chassis metal bracket  22 . Thus, the base metal bracket  12 , shield plate (right)  14 , and chassis metal bracket  22  are fitted and assembled.  
         [0075]    The shield plate (left)  13  is, in the same way as the shield plate (right)  14 , fitted to the chassis metal bracket  22 , and is assembled in the base metal bracket  12  and chassis metal bracket  22 .  
         [0076]    Further, the optical block  11  and shield plate (rear)  23  are assembled in the base metal bracket  12 , shield plate (right)  14 , shield plate (left)  13 , and chassis metal bracket  22 , and the shield unit is composed. In this manner, the shield unit of an integrally linked structure is obtained.  
         [0077]    In other words, the chassis metal bracket  22  functions as a printed board holding section for holding the signal board  20  and power source board  18 . The shield casing including the base metal bracket  12 , shield plate (left)  13 , shield plate (right)  14 , and shield plate (rear)  23  accommodates the optical block  11  and circuit unit (circuit block). The base metal bracket  12  functions as the optical block holding section for holding the optical block  11 .  
         [0078]    The shape of the ungula-shape-portions  12   a,    14   a  may be arbitrary, not limited to the shown shape. The shape of the fixing notch  22   a  and fixing hole  22   b  may be arbitrary, not limited to the shown shape.  
         [0079]    Mounting of the signal board  20  on the chassis metal bracket  22  is not limited to the shown method, but may include crimping, adhering or other arbitrary method.  
         [0080]    The mounting position of the ungula-shape-portion on the chassis metal bracket  22  is not specified.  
         [0081]    In this configuration, screw tightening is not needed in the chassis metal bracket  22 , base metal bracket  12 , shield plate (right)  14 , and shield plate (left)  13  of the invention. Therefore, the structure of the shield unit is simple. Yet, no limit is given to the fixing position of the printed board holding section, and mounting structure of high degree of freedom is realized.  
         [0082]    Further, when i) ungula-shape-portions  12   a  of the base metal bracket  12 , ii) ungula-shape-portions  14   a  of the shield plate (right)  14 , iii) ungula-shape-portions of shield plate (left)  13 , and iv) fixing notch  22   a  and fixing hole  22   b  of the chassis metal bracket  22  are arranged in multiple rows at predetermined intervals respectively, the interval between the electric grounding can be reduced. Therefore, an electrically stable shielding effect is obtained in this shield unit.  
         [0083]    (Embodiment 2)  
         [0084]    [0084]FIG. 5 is a sectional view of the circuit unit in this embodiment of the invention showing when it is drawn out at the time of servicing.  
         [0085]    As mentioned above, the shield plate (right)  14  has a plurality of ungula-shape-portions  14   a  in its inside, and the ungula-shape-portions  14   a  are inserted into the fixing notches  22   a  of the chassis metal bracket  22 .  
         [0086]    The shield plate (left)  13  is, in the same way as the shield plate (right), fitted to the chassis metal bracket  22 , and is assembled in the base metal bracket  12  and chassis metal bracket  22 .  
         [0087]    Therefore, as shown in FIG. 5, the serviceman removes the back cover  2  from the cabinet  1 , draws out the chassis metal bracket  22  backward, and fixes at an arbitrary position. As a result, the signal board  20  and other printed wiring boards can be serviced easily. Moreover, screw tightening is not needed in the chassis metal bracket  22  and shield plate (right)  14 , and no tool is needed. Hence, the service is done easily.  
         [0088]    (Embodiment 3)  
         [0089]    [0089]FIG. 5 also shows a sectional view before servicing of the optical unit in this embodiment of the invention.  
         [0090]    The structure before servicing is explained. The optical block  11  has a plurality of service hooks  24  in its inside. The service hooks  24  are inserted into the base metal bracket  12 . Fixing protrusions  24   a  of service hooks  24  are inserted into fixing holes  12   b  of the base metal bracket  12 . Further, the base metal bracket  12  and optical block  11  are compressed and fixed by the own weight of the optical block  11 , and are reinforced and fixed by colored screws  15   a.    
         [0091]    The shape of the service hooks  24 , fixing protrusions  24   a,  and fixing holes  12   b  are not limited to the shape shown in FIG. 5. The mounting position on the base metal bracket  12  by the colored screws  15   a  is not limited to the position shown in FIG. 5.  
         [0092]    In this configuration, the optical block is pressed to and conducts with the shield casing by its own weight. Therefore, the optical block  11  and base metal bracket  12  conduct securely with each other as shield casing, and electromagnetic shielding is assured. Besides, they are coupled by a small number of screws.  
         [0093]    Moreover, screw tightening is not needed around the fixing protrusions  24   a  and fixing holes  12   b  of the chassis metal bracket  22  and base metal bracket  12 , and servicing is easy and simple. Since the servicing screws are colored, they are not confused with other structural screws, and the servicing work is easy.  
         [0094]    [0094]FIG. 6 is a sectional view showing a state of lifting of optical unit when servicing in this embodiment.  
         [0095]    The optical block  11  has a plurality of service hooks  24  in its inside. The optical block  11  is lifted above the base metal bracket  12 . Further, the service hooks  24  and fixing protrusions  24   a  are inserted into the fixing notches  12   c  provided in the base metal bracket  12 , and the optical block  11  is supported by the base metal bracket  12 .  
         [0096]    In this configuration, the optical block  11  does not required servicing tool or fixing screw, and the service is simple and easy.  
         [0097]    Further, when dismounting the optical block, it can be provisionally fixed on the top of the shield casing. As a result, it is easy to work at the lower side or lateral side of the optical block when assembling or servicing the optical block.  
         [0098]    (Embodiment 4)  
         [0099]    [0099]FIG. 7 and FIG. 8 show sectional views after and before assembly of a conventional terminal board unit.  
         [0100]    [0100]FIG. 7 shows the mutual relation of terminal panel  104  and base metal bracket  112 , and front terminal unit  138  shown in FIG. 8. The front terminal unit  138  includes a front terminal board  119  and a front terminal metal bracket  121 , and is coupled to a signal board  120  and a chassis metal bracket  122 .  
         [0101]    In the conventional terminal board unit  138 , the front terminal board  119  is mechanically fixed to the front terminal metal bracket  121  by screws  15 . In this configuration, as shown in FIG. 7, undesired radiation  134  of electromagnetic wave may leak out from the gap between the base metal bracket  112  and the front terminal metal bracket  121  or front terminal board  119 , and the electromagnetic shielding effect is lowered.  
         [0102]    [0102]FIG. 9 and FIG. 10 show sectional views after and before assembly of a terminal board unit with protrusions according to the embodiment of the invention.  
         [0103]    [0103]FIG. 9 shows the mutual relation among terminal panel  4  and base metal bracket  12 , and front terminal unit  38  shown in FIG. 10. The front terminal unit  38  includes a front terminal board  19  and a front terminal metal bracket  21 , and is coupled to a signal board  20  and a chassis metal bracket  22 . Further, the front terminal metal bracket  21  has grounding protrusions  25 .  
         [0104]    In the front terminal unit  38 , the front terminal board  19  is mechanically and electrically fitted to the front terminal metal bracket  21  by screws  15 . Further, the front terminal metal bracket  21  is mechanically and electrically fitted to the chassis metal bracket  22  and signal board  20  by screws  15 . Moreover, the contact pressure is heightened by point contact of the grounding protrusions  25  provided in the front terminal metal bracket  21 , and the base metal bracket  12  and chassis metal bracket  22 , so that the contact resistance is lowered to conduct electrically.  
         [0105]    The shape of the grounding protrusions  25  is not limited to the shape shown in FIG. 9 and FIG. 10. Connection of the front terminal metal bracket  21  and chassis metal bracket  22  is not specified.  
         [0106]    In this configuration, screw tightening is not needed in the front terminal metal bracket  21  and the base metal bracket  12  of the shield casing of the invention. Therefore, servicing is easy and simple. In addition, the shielding effect against electromagnetic interference is enhanced.  
         [0107]    (Embodiment 5)  
         [0108]    [0108]FIG. 11 and FIG. 12 show sectional views after and before assembly of a terminal board unit with bends according to this embodiment of the invention.  
         [0109]    The material and structure of the front terminal unit  38  in this embodiment is basically the same as in embodiment 4. The assembling procedure of the front terminal unit  38 , and the mounting procedure of the base metal bracket  12  for composing the shield casing are also the same as in embodiment 4.  
         [0110]    What differs from embodiment 4 is that grounding bends  26  are provided instead of the grounding protrusions  25 , and their end faces are designed to contact elastically by cutting off the metal film of the outside wall of the front terminal metal bracket  21 .  
         [0111]    The taper shape of the grounding bends  26  is not limited to the shape shown in FIG. 11 and FIG. 12.  
         [0112]    Thus, electric contact between the front terminal metal bracket  21  and shield casing is assured, and secure shielding is realized.  
         [0113]    (Embodiment 6)  
         [0114]    [0114]FIG. 13 and FIG. 14 show sectional views after and before assembly of a terminal board unit with springs according to this embodiment of the invention.  
         [0115]    The material and structure of the front terminal unit  38  in this embodiment is basically the same as in embodiment 4. The assembling procedure of the front terminal unit  38 , and the mounting procedure of the base metal bracket  12  for composing the first shield casing are also the same as in embodiment 4.  
         [0116]    What differs from embodiment 4 is that grounding springs  27  are provided instead of the grounding protrusions  25 , and their end faces are designed to couple electrically and contact elastically with the outside wall of the base metal bracket  12  and outside wall of the front terminal metal bracket  21 . The grounding springs  27  are crimped and fitted to the terminal panel  4 , and the terminal panel  4  is fastened to the base metal bracket  12  by screws  15 .  
         [0117]    The shape of the grounding springs  27  is not limited to the shape shown in FIG. 13 and FIG. 14. The mounting method of the grounding springs  27  on the terminal panel  4  is not limited, and may include welding, adhering or other methods.  
         [0118]    (Embodiment 7)  
         [0119]    [0119]FIG. 15 and FIG. 16 show sectional views after and before assembly of a terminal board unit with gaskets according to this embodiment of the invention.  
         [0120]    The material and structure of the front terminal unit  38  in this embodiment is basically the same as in embodiment 6. The assembling procedure of the front terminal unit  38 , and the mounting procedure of the base metal bracket  12  for composing the first shield casing are also the same as in embodiment 6.  
         [0121]    What differs from embodiment 6 is that conductive gaskets  28  are provided instead of the grounding springs  27 , and their end faces are designed to couple electrically and contact elastically with the outside wall of the base metal bracket  12  and outside wall of the front terminal metal bracket  21 . The shape of the conductive gaskets  28  is not limited to the shape shown in FIG. 15 and FIG. 16.  
         [0122]    (Embodiment 8)  
         [0123]    [0123]FIG. 17 and FIG. 18 show sectional views before and after assembly of cover unit with springs according to the embodiment.  
         [0124]    [0124]FIG. 19 is a plane view of lamp shield plate of the embodiment, particularly showing the relation of the lamp shield plate  8  and its grounding springs  8   a.    
         [0125]    In FIG. 17, the lamp shield plate  8  is mechanically fitted to the resin-made lamp cover  7  by crimping. Further, as shown in FIG. 18, the lamp cover  7  is fixed to the base metal bracket  12  by screws  15 . At this time, the grounding springs  8   a  provided in the lamp shield plate  8  contact elastically and conduct electrically with the cut-off section of the opening  12   d  of the base metal bracket  12 . The shape of the grounding springs  8   a  is not limited to the shape shown in FIG. 17, FIG. 18 and FIG. 19. Method of connection of lamp cover  7  and lamp shield plate  8  is not limited to crimping only.  
         [0126]    In this configuration, the grounding springs  8   a  of the lamp shield plate  8  assure stable conductivity with the base metal bracket  12  of the shield casing regardless of its surface treatment state. Therefore, the shielding effect against the electromagnetic interference is enhanced. Also in this configuration, screw tightening between the shield casings is not needed, and the shield structure is simplified. Only screws for tightening the structural elements are needed, and the number of necessary screws is decreased.  
         [0127]    When grounding springs  8   a  are disposed in multiple rows at predetermined intervals, intervals between the electric grounding can be narrowed. Hence, electric shielding is assured in stable condition.  
         [0128]    (Embodiment 9)  
         [0129]    [0129]FIG. 20 and FIG. 21 are side views before and after assembly of power source circuit unit of the invention, and FIG. 22 shows a sectional view after assembly of power source circuit unit of the invention.  
         [0130]    In FIG. 20, a power source shield  17  is attached to a chassis metal bracket  22  by screws  15  so that a plurality of grounding legs  29  provided at the side of the power source shield  17  may penetrate through slots  18   a  provided in a power source board  18  attached to the chassis metal bracket  22 . At this time, as shown in FIG. 21, the screws  15  tighten the power source board  18  together with the chassis metal bracket  22  and fix the board  18  to the chassis metal bracket  22 . Herein, the top of the chassis metal bracket  22  elastically contacts with the grounding legs  29 .  
         [0131]    In this configuration, the shield unit is integrally linked, and the power source board  18  is enclosed in a simple structure, and is shielded electrically.  
         [0132]    The shape and position of the grounding legs  29  and slots  18   a  are not limited to those shown in FIG. 21 and FIG. 22. Method of mounting of power source board  18  and power source shield  17  on the chassis metal bracket  22  is not limited, and may include crimping, adhering or other methods.  
         [0133]    In this configuration, there are only few screw tightening portions in the chassis metal bracket  22 , power source board  18 , and power source shield  17 . Hence, the shield unit is simplified in structure.  
         [0134]    When grounding legs  29  and slots  18   a  are disposed in multiple rows at predetermined intervals, intervals between the electric grounding can be narrowed. Hence, electric shielding is assured in stable condition in this shield unit. Further by direct conduction between the grounding legs  29  and power source board  18  by spring or solder, a more stable electric shielding is obtained. Besides, since the weight of the power source shield  17  or impact of falling or vibration is not applied directly to the power source board  18 , an effective mechanical strength of the power source board  18  is assured.  
         [0135]    (Embodiment 10)  
         [0136]    [0136]FIG. 22 is a sectional view of cooling structure of power source circuit unit having a cooling fan.  
         [0137]    The cooling structure is explained. In FIG. 22, a fan  16  is disposed in a power source shield  17 . A plurality of grounding legs  29  disposed at the side of the power source shield  17  penetrate through slots  18   a  disposed in a power source board  18  attached to a chassis metal bracket  22 . Screws  15  tighten the power source shield  17 , power source board  18 , and chassis metal bracket  22  together. Thus, mechanically, the cooling structure for cooling the power source board  18  is linked integrally.  
         [0138]    Herein, intake air  16   a  passes through an intake port  17   a,  and is sucked into this cooling structure, and after cooling the power source board  18 , it is blown out from an exhaust port  17   b  as exhaust  16   b.    
         [0139]    The shape and position of the grounding legs  29  and slots  18   a  are not limited to those shown in FIG. 22. Method of mounting of power source board  18  and power source shield  17  on the chassis metal bracket  22  is not limited, and may include crimping, adhering or other methods. The shape and position of the fan  16 , intake port  17   a,  and exhausts port  17   b  are not limited but are arbitrary.  
         [0140]    In this configuration, there are only few screw tightening portions in the chassis metal bracket  22 , power source board  18 , and power source shield  17 , and the cooling structure is simplified.  
         [0141]    Since the gap between the power source shield  17  and power source board  18  is small, the cooling structure is excellent in air tightness.  
         [0142]    When the grounding legs  29  and slots  18   a  are arranged in multiple rows at predetermined intervals, the physical space gap is small and the air tightness is enhanced. Therefore, a highly efficient cooling structure is realized.  
         [0143]    (Embodiment 11)  
         [0144]    [0144]FIG. 23, FIG. 24, and FIG. 25 show top view, side view, and rear view after assembly of external shield components of the invention.  
         [0145]    [0145]FIG. 26 shows a top sectional view and detailed view after assembly of external shield components, and FIG. 27 is a side view before assembly of external shield components.  
         [0146]    A shield plate (rear)  23  forming the shield casing has a plurality of ungula-shape-portions  23   b,  protrusions  23   a,  and guides  23   c  on its outer circumference. In a shield plate (right)  14 , the ungula-shape-portions  23   b  having protrusions  23   a  are inserted by snapping in, and by cutting off the metal surface film by force, the shield plate (right)  14  and shield plate (rear)  23  conduct electrically, and the shield casings securely conduct electrically. Thus, the shield casings are integrally linked. The screws  15  fix screw portions  14   b  and screw portions  23   d.    
         [0147]    The base metal bracket  12  and shield plate (rear)  23  are fixed by screws  15  as shown in FIG. 24. At this time, the shield plate (right)  14  is pressed to the base metal bracket  12 , and the both conduct electrically.  
         [0148]    The shield plate (left)  13  is similarly coupled to the base metal bracket  12  and shield plate (rear)  23 , and conduct electrically. Thus, the shield casing, in which the base metal bracket  12 , shield plate (rear)  23 , shield plate (right)  14 , and shield plate (left)  13  are integrally linked, is obtained.  
         [0149]    The shape of the ungula-shape-portions  23   b,  protrusions  23   a,  and guides  23   c  is not limited to the shown shape. The mounting position on the shield plate (right)  14  by ungula-shape-portions is not specified. The shape and position of the screws  14   b  and screws  23   d  are arbitrary.  
         [0150]    In this configuration, the shield plate (rear)  23 , shield plate (right)  14 , shield plate (left)  13 , and base metal bracket  12  conduct securely with each other. At the same time, screw tightening portions for their coupling can be decreased in number. Thus, the shield casing is realized in a simple structure. When ungula-shape-portions  23   b  and guides  23   c  are disposed in multiple rows at predetermined intervals, intervals between electric grounding can be decreased. Therefore, the shield casing supplies a stable electric shield.  
         [0151]    (Embodiment 12)  
         [0152]    [0152]FIG. 28 shows undesired reflected light after assembly of projection lens and optical block in a prior art, and FIG. 29 shows effective light and undesired light after assembly of projection lens and optical block in a prior art.  
         [0153]    In the conventional optical block  111  shown in FIG. 28 and FIG. 29, the projection lens shield  110  has an open space for allowing the movable range of the projection lens  109  having movable mechanism. In this configuration, however, undesired reflected light  131  may leak out from the gap between the projection lens shield  110  and projection lens  109 , and may be emitted to the screen to lower the picture quality. Besides, the undesired light emitted from the inside of the projection lens  109  may be also emitted to the screen to lower the picture quality.  
         [0154]    As shown in FIG. 29, the projection lens  109  emits effective light  132  and undesired light  133  from the opening of the lens shield  110 .  
         [0155]    To solve these problems, hitherto, complicated works were required such as manual adhesion of non-woven cloth or subsequent mounting process of light shielding components.  
         [0156]    [0156]FIG. 30, FIG. 31, and FIG. 32 show top view, side sectional view and bottom view of projection lens shield and light shielding screen of the invention.  
         [0157]    [0157]FIG. 33 is a side sectional view after assembly of projection lens shield of the invention.  
         [0158]    A light shielding screen  30  integrated with the projection lens shield  10  by crimping is disposed on the top of the projection lens  9 . The light shielding screen  30  shuts off the undesired reflected light  31  emitted from the outer periphery of the projection lens and the undesired light  33  emitted from the inside of the projection lens. The shape and position of the projection lens shield  10  and light shielding screen  30  are not particularly specified. Herein, the light shielding screen  30  is disposed so as not to spoil the movable range of the projection lens  9 . Method of mounting of the light shielding screen  30  on the projection lens shield  10  is not limited to crimping, but may include adhesion or other methods.  
         [0159]    In this configuration, a simple light shielding structure without manual adhesion of non-woven cloth or subsequent mounting process of light shielding parts may be obtained. Further, the weight of the projection lens  9  or impact of falling or vibration may not be directly applied to the projection lens shield  10  or light shielding screen  30 , so that it is excellent in mechanical strength and positional precision.  
         [0160]    (Embodiment 13)  
         [0161]    [0161]FIG. 34 and FIG. 35 are side sectional views after assembly of projection lens shield in the embodiment of the invention.  
         [0162]    The material and structure of the projection lens shield  10  and light shielding screen  30  in this embodiment are basically the same as in the preceding embodiment 12.  
         [0163]    What differs from embodiment 12 is that the slope shape of the projection lens shield  10  is changed from the shape in FIG. 33 as shown in FIG. 34.  
         [0164]    Herein, the light shielding screen  30  on the top of the projection lens  9  cuts off undesired light  33  emitted from the inside of the projection lens  9 , and the projection lens shield  10  which is a structure integral with the light shielding screen cuts off a part of undesired light  33  not shielded by the light shielding screen  30 .  
         [0165]    That is, the undesired light emitted from the projection lens is cut off in double light shielding structures of the light shielding screen on the top of the projection lens and the structure integral with the light shielding screen. The structure of the projection lens shield  10  may be formed by adhering two parts as shown in FIG. 35.  
         [0166]    In this configuration, the light shielding quantity and the light shielding precision are enhanced.  
         [0167]    (Embodiment 14)  
         [0168]    [0168]FIG. 36 shows undesired radiation of electromagnetic wave after assembly of conventional projection lens and optical block.  
         [0169]    The conventional projection lens shield  10  is disposed so as to keep a gap to the projection lens  9  in order to maintain the movable range of the projection lens  9  having a movable mechanism. However, in this configuration, undesired radiation  34  of electromagnetic wave may leak out from the gap between the projection lens shield  10  and projection lens  9 , and a the shielding performance is lowered.  
         [0170]    To solve these problems, hitherto, complicated works were required such as manual adhesion of conductive non-woven cloth or subsequent mounting process of conductive components.  
         [0171]    [0171]FIG. 37 and FIG. 38 show side sectional view and bottom view of projection lens shield and conductive spring of the invention.  
         [0172]    [0172]FIG. 39 and FIG. 40 show side sectional view after and before assembly of projection lens shield of the invention.  
         [0173]    As shown in FIG. 37 and FIG. 38, a conductive spring  35  is integrally fitted to the projection lens shield  10  by crimping.  
         [0174]    As shown in FIG. 39, the conductive spring  35  integrated with the projection lens shield  10  by crimping is disposed on the top of the metal projection lens  9  so as to contact elastically and conduct electrically. As a result, undesired electromagnetic radiation  34  leaking out from the periphery of the projection lens can be cut off.  
         [0175]    The shape and position of the projection lens shield  10  and conductive spring  35  are not particularly specified. The movable range of the conductive spring  35  allows the projection lens  9  to be movable while keeping electric contact with the spring  35 . Method of mounting of the conductive spring  35  on the projection lens shield  10  is not limited, but may include adhesion, fusion or other methods.  
         [0176]    In this configuration, a simple shielding structure of excellent shielding performance is obtained without requiring manual adhesion of conductive non-woven cloth or subsequent mounting process of conductive components. Further, the weight of the projection lens  9  or impact of falling or vibration is not directly applied to the projection lens shield  10 , so that it is excellent in mechanical strength and positional precision.  
         [0177]    (Embodiment 15)  
         [0178]    [0178]FIG. 41 and FIG. 42 show side sectional view and bottom view of projection lens shield and conductive spring of the invention.  
         [0179]    [0179]FIG. 43 and FIG. 44 show side sectional view after and before assembly of projection lens shield of the invention.  
         [0180]    In this embodiment, the material and structure of the projection lens shield  10  and conductive spring  35  are basically the same as in the preceding embodiment 14.  
         [0181]    What differs from embodiment 14 is that, as shown in FIG. 42, a plane  36  parallel to the projection lens surface is disposed on the projection lens shield  10 , so as to increase the degree of freedom of mounting structure of the conductive spring  35 . In this configuration, deformation of the conductive spring  35  can be prevented when inserting the projection lens  9  into the projection lens shield casing. It is also easy to increase the number of conductive springs  35 . Therefore, the reliability and performance of shielding are further enhanced.  
         [0182]    (Embodiment 16)  
         [0183]    [0183]FIG. 44 and FIG. 46 show side sectional view and bottom view of projection lens shield and conductive gasket of the invention.  
         [0184]    [0184]FIG. 47 and FIG. 48 show side sectional view after and before assembly of projection lens shield of the invention.  
         [0185]    In this embodiment, the material and structure of the projection lens shield  10  are basically the same as in the preceding embodiment 15.  
         [0186]    What differs from embodiment 15 is that the conductive gasket  37  is used instead of the conductive spring  35 . The same effects as in embodiment 15 are obtained.  
         [0187]    Thus, the electric shield casing and optical shield casing of the invention are high in the degree of freedom of mounting without sacrificing the servicing merits.  
         [0188]    Throughout the embodiments, the plate members used in electromagnetic shielding such as base metal bracket, shield plate, and chassis metal bracket are made of metal, and can be formed by plate working. Incidentally, when these members contain conductive members, the entire members may not be always made of metal.