Repair of VCRs and video players. LMP in SHARP devices. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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SHARP video recorders (video players) of early releases with an asymmetrical cassette receiver often fail due to malfunction of the CVL elements. The defects discussed below in most devices (such as VC-6V3, etc.) appear after two to three years, depending on the intensity of use. This is caused, as practice has shown, by design flaws of the CVL, as well as non-compliance with the rules of use.

The appearance of the CVL components of the SHARP-VC-6V3 video player from different sides is shown in Fig. 1-4. The list of the most common malfunctions does not include cases associated with defects in the CVL and BVG themselves, which affect the quality of recording and playback, since they are described in some detail in the technical literature, and they are inherent in all types of such devices. Malfunctions of the cassette receiver, software switch and idler gear assembly strip will be described here.

1. The cassette does not fill, the fill motor does not rotate

First check the power source. To do this, use a voltmeter to measure (if possible) its output voltage at the connector (Fig. 1, item 1).

Then they check the refueling engine control chip. It is easy to find - it is installed perpendicular to the printed circuit board and has 9 or 10 pins. The power supply pins of the refueling motor are connected directly to its terminals.

The control chip can be BA6209, BA6218, BA6219B or BA6418. Their block diagrams are shown in Fig. 5-8 respectively.

(click to enlarge)

Make sure that the supply voltage is supplied to the microcircuit from the power source. It is usually equal to 12 V. If there is no supply voltage at the terminals of the microcircuit, check the serviceability of the elements connected between the power source and the microcircuit (for example, blocking capacitors and breaking resistors in Fig. 5).

It happens that the supply voltage reaches the control chip, but the refueling engine still does not turn on. Then check the engine itself (see Fig. 1, item 4). To do this, disconnect (if possible) the connector that is connected to the software mechanism assembly (see Fig. 1, item 3), or unsolder the power wires of the refueling engine. A voltage of 12 V in any polarity is supplied to the motor terminals from an external power source. The rotation of the latter indicates its serviceability.

You should also make sure that there is supply voltage at the terminals of the device’s microcontroller (usually +5 V). Next, check the integrity of the conductors from the microcontroller to the refueling engine control chip (see Fig. 5-8).

Then they check the correct operation of the mechanical sensor for refilling the video cassette, located on the sensor board of the cassette receiver (see Fig. 1, item 8). In the initial state, its contacts should be closed. When a video cassette is inserted, they open. In order to have access to the sensor, remove the front panel of the device (it is fixed on plastic latches), disconnect the flexible cable from the sensor board (see Fig. 1, item 7), unscrew the two screws securing the cassette receiver to the CLM frame (often these screws painted over with red paint) and remove the belt (see Fig. 1, pos. 5) from the refueling engine. After that, slightly shaking, remove the cassette receiver. With the cassette receiver removed, a video cassette is inserted and, by lightly pressing it in the direction of travel, the operation of the cassette refill sensor is controlled.

If all these actions do not ultimately resolve the malfunction, the device’s microcontroller must be replaced.

Before reinstalling the cassette receiver in the LPM, pay attention to the fact that the cassette receiver bed is in the extreme forward position (see Fig. 2, item 1). If it has gone deep, by rotating the filling motor shaft (Fig. 1, pos. 6) it is shifted to the extreme forward position.

2. The “Stop” and “Eject Cassette” commands from the “Playback” or “Record” position are not executed.

When executing these commands, the CVL must remove the tape from the BVG and reversely (first in one direction, then in the other direction) rewind the cassette for 1...2 s in each direction, and then unload the cassette. Rewinding a video cassette is perceived by ear as two loud clicks with an interval of 2...3 s.

3. Videotape does not rewind in one or both directions

4. The device is unstable: at first, some LPM control command is processed, and after a while it is not executed

The common cause of these malfunctions (p. 2, 3, 4) may be the electromechanical desynchronization of the LPM or the malfunction of its elements. It is also possible a malfunction of the microcontroller and the control unit of the LPM elements, but they will be discussed in the following articles.

In order to eliminate these defects, the serviceability of the LPM elements is checked. First, remove the front panel and cassette (see paragraph 1). Then unscrew the three screws located along the perimeter that fasten the refueling engine assembly to the LPM (see Fig. 1, pos. 2). Remember (mark) the position of the program bar (see Fig. 3 and Fig. 4, pos. 6), its rocker (see Fig. 3, pos. 3; Fig. 4, pos. 5) and the pressure roller rocker (see Fig. 3, item 2). Disconnect the connector (see Fig. 1, pos. 3) and, slightly shaking the body of the refueling engine assembly, remove it from the side of the LPM.

If the device is in the “Stop” position, check the correct alignment of the marks of the program switch (see Fig. 3, pos. 7, 8). They should be one opposite the other.

Then make sure that the software switch is working properly. To do this, remove the disk from it (most often red, yellow or white, Fig. 3, item 5), releasing the fastening latches in the inner hole. Check the integrity of the contact pads and spring contact, wash them with alcohol and lubricate them with a small amount of technical petroleum jelly or special lubricant. Assemble the program switch.

They monitor the integrity of film resistors sprayed onto the board of the refueling motor assembly (in the SHARP-VC-6V3 model they are designated as RB21-RB25).

Next, remove the lock washer securing the pressure roller rocker arm (see Fig. 3, item 2) and remove the rocker arm. Remember (mark) the position of the program gear and also remove it.

Two rocker arms are released from below: the program bar (see Fig. 3, item 3) and the bar for the device for threading the tape into the BVG (not shown in the figure). The teeth of both strips are fixed in the grooves of the program gear. It is very important to remember (mark) the position of their teeth in its grooves.

Check the integrity of the program gear grooves both from above and from below. Carefully remove excess lubricant from the gear and apply it to the entire surface of the grooves. It is not advisable to use another lubricant for these purposes (for example, litol).

Also, with a small amount of removed grease, the fastening pins of the program gear (see Fig. 3, item 1) and the retard gear (see Fig. 3, item 4) are treated.

If the program gear is in good order, install it in place, making sure that the teeth of the rocker arm of the program bar and the tape feeder in the BVG fall into the corresponding grooves of the gear. Replace the pressure roller rocker arm and secure it with a lock washer. By manually reversing the program gear, the operation of the mechanical components is checked: movement of the program bar, change in the height of the position of the intermediate gear (Fig. 4, item 3), movement of the belt filling rollers in the BVG forward and backward until it stops, movement of the pressure roller to the drive shaft ( see Fig. 1, pos. 10, 11).

Particular attention is paid to ensuring that the software gear rotates without excessive force. The maximum resistance to its rotation is created by the program bar, therefore, at the moment of greatest resistance of the gears, lubricant is added to those nodes that interfere with the forward movement of the bar (see Fig. 4, pos. 7-9). By reversely rotating the program gear, the lubricant is “smeared” along the program bar. Lubricant is removed from device components that have excess grease, or purchased (it is called LPM lubricant for VCRs).

Next, set the program gear to its original position, as shown in Fig. 3. Combine the risks of the program switch (light triangle opposite the black one) and install the refueling motor assembly on the CVL so that the cut of the program gear rod coincides with the cut of the hole of the program switch (see Fig. 3). Fix the refueling motor assembly to the CVL with three screws.

Then remove the main and intermediate gears (see Fig. 4, items 1 and 3, respectively), lubricate them and install them in place. Particular attention is paid to the ease of movement of the intermediate gear up and down without sticking in extreme positions. You should check the ease of rotation of the reel bearings (see Fig. 4, items 4 and 10), having first freed them from the brake pads.

After this, install the cassette receiver in place and put its belt on the refueling motor shaft (see Fig. 1, pos. 5, 9, respectively). Screw in the screws securing the cassette receiver.

You need to make sure that the belts that fit the refueling engine shaft fit tightly and do not slip on the pulleys. Make sure that the belt installed between the drive shaft motor and the main gear is of good quality (see Fig. 4, item 1). Once again check the assembly quality of the elements, connect the connector to the filling motor assembly (see Fig. 1, item 3) and the cable (see Fig. 1, item 7) to the cassette receiver sensor board (see Fig. 1, item 8). XNUMX).

Finally, turn on the device and monitor the performance of the CVL. If the malfunction has not been eliminated, more carefully check the elements of the CVL, the serviceability of the photo sensors for the movement of the subcoils (located under them) and the cassette receiver, as well as the transistors located on the photo sensor board of the cassette receiver. If there are no defects, replace the microcontroller.

The article does not say anything about drive shaft motor malfunctions, but more on that another time. Let's give some tips on CVL maintenance:

1. In LPM, a special lubricant of mechanical units is used, the domestic analogue of which is not commercially available. If it is necessary to lubricate certain elements, carefully remove its excess from other nodes.

2. It is recommended to check the condition of belts and BVG at least once a year.

3. The BVG, as well as the magnetic heads of the synchronization and sound circuits, should be cleaned with thin lint-free cambric soaked in alcohol. The cambric movements when cleaning should occur along the direction of movement of the magnetic tape with light pressure. A good replacement for alcohol is the special liquid included with cleaning floppy disks for personal computers.

4. There is no need to get carried away with adjusting the internal brake of the subcoils. If the felt pad underneath has worn out, it should be replaced. If you use faulty (“stiff”) video cassettes, the reels may not rotate. If you increase the internal braking in them (increase the friction between the felt ring and the plastic rings of the reel braking device), then problems may arise when working with working video cassettes.

Author: A.Rodin, Moscow

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