JPH0438580Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The invention relates to local oscillation circuits such as television tuners, and more specifically, sub-assembles the resonant circuit portion in which the resonant frequency is adjusted by advancing and retracting screws. The purpose is to facilitate assembly and improve accuracy and reliability.

2. Description of the Related Art After assembly of a local oscillation circuit for a television tuner, it is necessary to adjust the variable frequency range.

For example, in the case of a local oscillation circuit for a second mixer in a CATV converter, this adjustment is performed using the following configuration.

That is, as shown in Fig. 5, using a screw 2 inserted as a core into the tuned coil 1 constituting the LC resonant circuit, this screw 2 is screwed into the screw hole of the chassis base 3 from the outside, and by inserting and removing it, the screw 2 is inserted as a core. I'm making adjustments.

Problems to be Solved by the Invention In the above-mentioned adjustment method in which the screw 2 is screwed into the chassis base 3, the screw 2 protrudes outside the tuner, which obstructs the installation into the television set and reduces space utilization. do. Furthermore, if the relative position of the screw 2 and the tuning coil 1 changes due to the application of an external impact, the adjustment will be disrupted, so the adjustment must be handled with care, resulting in a problem of reduced workability.

Means for solving the problem In order to solve the problem caused by the adjustment screw protruding outside the tuner,
The local oscillator circuit consists of a sub-assembled body in which a support plate is assembled with tuning parts, in which a screw that advances and retreats as a core is screwed onto a tuning coil on a metal plate, and the screw is inserted into a through hole drilled in the shield base. Correspondingly, it is mounted on a printed circuit board within the shield base.

Effect: According to the above configuration, the adjustment screw is completely hidden inside the tuner case, so the above problem is completely solved.

In addition, since the local oscillator circuit of the present invention is sub-assembled on the metal plate, including adjustment screws, it is easier to assemble, especially when changing the relative position between the chassis base and the printed circuit board. This has the advantage of eliminating characteristic fluctuations.

Embodiment An embodiment in which the present invention is applied to a local oscillation circuit of a CATV (cable television) converter will be described.

Figures 1 and 2 show the LC resonant circuit B of the local oscillation circuit A of the CATV converter shown in Figure 3.
Shown assembled inside the shield base.

Before explaining Figures 1 and 2,
The structure and function of local oscillation circuit A shown in the figure will be briefly explained. Reference numeral 10 denotes an amplifier circuit mainly composed of a transistor 11. The LC resonant circuit B is
Tuned coil 1 with screw 12 inserted as a core
3. It is composed of a capacitor 14, a disk-shaped capacitor 15, and a variable capacitance diode 16, and feedthrough capacitors 17, 18, and 19 are arranged at key points.

Note that 20 is a circuit that supplies an operating voltage (+B) to the transistor 11, and 21 is an AFC voltage supply circuit to the variable capacitance diode 16.

This local oscillation circuit A outputs an oscillation output () at a frequency according to the capacitance of the variable capacitance diode 16 determined by the AFC voltage to the second output of the CATV converter.
It is supplied to the mixing circuit, and the variable range of the oscillation frequency by the AFC voltage is adjusted by the insertion length of the screw 12 into the tuning coil 13.

In FIGS. 1 and 2 showing the state in which the LC resonance circuit 13 is assembled to the tuner, 22 is a chassis base, 23 is an adjustment through hole drilled in the chassis base 22, and 24 is another tuner component (not shown). The assembled printed circuit board 25 is a shield partition plate erected on the printed circuit board 24. 26
is a metal plate serving as the base of the subassembly, which is connected to earth, and on which the metal capacitor 14 and feedthrough capacitors 17, 18, and 19 are mounted by soldering. The synchronous coil 13 is soldered onto a metallic capacitor 14 and a feedthrough capacitor 17, and is fixed to a metal plate 26 via these. Also, disk type capacitor 1
5 is attached by passing its leads through the feedthrough capacitors 17 and 18, and the variable capacitance diode 16
is attached by inserting its leads into feedthrough capacitors 18 and 19.

27 is a support plate, the lower edge of a rectangular holding part in which a screw hole 27a is formed is soldered onto the metal plate 26, and both side edges of the support plate are connected to the shield partition plates 25 and 2.
5, and the tip of an extension piece 27b that is bent from the upper edge of the holding part and extends over the tuning coil 13 is soldered to the opposing shield partition plate 25. The screw 12 is
With its head facing the through hole 23 of the chassis base 22, hold the screw hole 27a of the support plate 27.
The tuning coil 13 is screwed onto and held by the tuning coil 13.
It is loosely inserted inside. 28 is a lock nut for fastening the screw 12 to the support plate 27.

As shown in FIG. 4, the holding part in which the screw hole 27 of the support plate 27 is formed has a structure in which an elastic plate 29 made of plastic or the like is sandwiched, and the contraction force of the elastic plate 29 is used to tighten the screw 12. It may be tightened.

The LC resonant circuit 13 is assembled by subassembling all the components onto the metal plate 26 in advance, and then onto the printed circuit board 24 together with the shield partition plate 15 and the like. At this time, the feedthrough capacitor 17,1
The end portions of the leads passing through 8 and 19 are soldered to the wiring pattern on the printed wiring board to make an electrical connection. Note that the support plate 27, which is soldered to the adjacent shield partition plate 15 at this time, may be integrated with the metal plate 26 during this assembly.

To adjust the local oscillation circuit A having the above structure, insert an adjustment driver through the through hole 23 of the chassis base.
This is done by rotating the screw 12.

Effects of the invention According to the invention, the LC resonant circuit B of the local oscillator circuit A is constructed as a sub-assembly structure using metal plates, and the adjustment screws are held on the support plate, making it easy to assemble the tuner itself. In addition to making the work easier, there is no protrusion to the outside of the shield base, making it easier to assemble into the television set.

Further, since the LC resonant circuit is also shielded by a metal plate and a support plate and is coupled to other circuits through a feedthrough capacitor, temperature resistance, moisture resistance characteristics, and adjustment accuracy can be improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the LC resonant circuit portion of a local oscillation circuit that is an embodiment of the present invention, Fig. 2 is a perspective view of the LC resonant circuit portion shown in Fig. FIG. 4 is a side view showing another embodiment of the support plate shown in FIG. 1. FIG. 5 is a partial sectional view of a tuner showing the mounting structure of the adjustment screw of a conventional local oscillation circuit. A...Local oscillation circuit, B...LC resonant circuit, 1
2... Screw, 13... Tuning coil, 22... Chassis base, 23... Through hole, 24... Printed circuit board, 26... Metal plate, 27... Support plate.

Claims (1)

[Scope of utility model registration request] A sub-assembled body is assembled with a support plate, in which a screw that advances and retreats as a core is screwed onto a tuning coil on a metal plate, along with tuning parts, and the shield is assembled by aligning the screws with the through holes drilled in the shield base. A local oscillation circuit characterized by being mounted on a printed circuit board within the base.