Power supply and electric drive systems of modern camcorders - troubleshooting, repair. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Repair of video cameras (camcorders) is one of the most difficult in household video equipment. This is due to a high degree of control over the operation of their nodes and its blocking in case of malfunctions. The published article describes the repair of such devices using the SAMSUNG VP-U2 camcorder as an example.

Camcorders are highly complex consumer electronics products. Their qualified repair can only be done by experienced specialists in the presence of service documentation, modern measuring equipment, equipment and spare parts. Of the companies that provide warranty repairs for video cameras sold in Russia and the CIS, the best known are SONY MATSUSHITA (PANASONIC), SAMSUNG. They have equipped a relatively large number of their service centers with everything necessary. HITACHI, SHARP, JVC and some others have done much less in this respect. Camcorders from companies such as CANON, FISHER, ORION, UNIVER-SUM, etc. outside of Moscow can only be repaired by ordinary workshops or individual specialists.

The terms of warranty service are basically identical for all companies selling video cameras in Russia. Let's consider them on the example of the South Korean company SAMSUNG, which sells affordable VIDEO-8 format camcorders (SAMSUNG: VP-U10 for $415, VP-H66 for $420 - this is for the summer of 1997). The terms of service contain five points: 1 - warranty period of 12 months (SONY gives a two-year period); 2 - the warranty covers only the cost of spare parts and labor costs, i.e. the transportation of equipment is provided at the expense of the client, which is very burdensome in our conditions (about 30 authorized service centers of SAMSUNG are located in a number of regional centers); 3 - repairs must be carried out exclusively in authorized service centers; 4 - the warranty does not cover video heads, pierced and deformed cases, etc.; 5 - The warranty does not cover damage caused by accident, misuse, fire, flood, or devices repaired by other workshops.

In addition, the warranty is valid only when the warranty card is filled out (name, address, phone number of the buyer, address, signature and stamp of the dealer). Consequently, a huge amount of equipment sold in the markets, in stalls, privately imported from abroad, etc., was out of warranty service. An even bigger headache for camcorder owners is delivered by faulty equipment after the warranty period or manufactured by companies that do not have service representatives in Russia. Given this, it is quite justified to publish materials for experienced radio amateurs and video camera repair specialists.

According to the author's observations, a significant number of faults in modern camcorders fall on systems that provide power to all their components and engines. Video cameras are characterized by the multifunctionality of such systems, so the use of the terms "power source", "electric drive", "stabilizer", etc. is not entirely correct.

One of the most important requirements for video cameras is to ensure low current consumption from autonomous power sources. For most devices of VHS-C and VIDEO-8 formats, power consumption is in the range of 5...10 W. Especially low power is consumed by SONY video cameras with the STAMINA function, for example, in SONY - CCD-TR820E it is only 3,5 W [1]. Such impressive characteristics are obtained by minimizing the current consumption of the electronic part of the cameras and a significant increase in the efficiency of power supply systems, the circuitry of which is much more complex than in other types of household equipment.

On fig. 1 shows a simplified circuit diagram of the power supply system of the SAMSUNG VP-U12 camcorder. It is based on a switching voltage converter (DC / DC CONVERTOR), a constant voltage of 6 V is supplied from a battery (NP - 7HPN, etc.) or from an AA - E2P network adapter, which is a switching power supply combined with a charger. The primary voltage through the B900 battery terminal and pin 12 of the CN901 connector comes to the control and auto-regulation system. In it, without any switching, it passes through the voltage regulator on the IC501 chip (at the output - +5 V) to pin 89 (VDD) of the IC503 control microprocessor of the CXP80724 type from SONY.

(click to enlarge)

The further operation of the voltage converter is completely dependent on the microprocessor commands, and many output voltages are covered by the control system, and if one of them deviates from the norm, the operation of the converter is blocked. This algorithm of operation is typical for most modern video cameras. This sometimes causes difficulties during diagnostics, since it is very problematic to check something in a few seconds of the active state after switching on. Under certain conditions, manual activation of most converters is possible. But if it is impossible to turn off the converter, it is necessary to check all its output circuits and power elements.

In the absence of short circuits to a common wire and punched elements, you can use the manual start mode. In this case, this is done by closing contacts 10, 11 and 12 of the CN901 connector. This opens the key on the Q902 transistor and +6 V is supplied to pin 24 of the multifunctional microcircuit IC901. All converter stabilizers are made according to key circuits and are covered by feedback so that the output voltages are stabilized by changing the duty cycle of the pulses coming to the keys from the IC901 chip. Due to this, a high efficiency of the converter as a whole is ensured, there is no need to remove heat from it, and the use of high-performance semiconductor devices and elements for surface mounting made it possible to place it on a very small printed circuit board.

Most of the video camera devices are powered by +5 V from a key stabilizer on transistors Q908, Q909 (starting from pin 19 - OUT5 of the IC901 microcircuit) with a short circuit protection device (the emergency mode corresponds to a high resistance of the key on transistor Q907).

The +902 V voltage set by the VR5 resistor is supplied to the control and autoregulation systems (SS5V circuit), through the L911 choke - to the sound channel, through the L912 choke - to the image channel, and through the key on the Q911 transistor - to the chamber part of the camcorder. The voltages +15 V (CAM.15V), +20 V (CAM.20V), -10 V (CAM.-10V) required to power the nodes of the chamber part form a pulse cascade on transistors Q913, Q914, transformer T901 and diode assembly D907. The voltage +15 V is set with a trimming resistor VR903.

In addition to the stabilizers themselves, the converter includes a part of the components of the auto-regulation system of the camcorder's video recorder.

The BVG ACS includes a key voltage driver on Q950, Q951 transistors, an L951C954C955 filter, an error signal amplifier on an IC903 chip (TA75501F op-amp from TOSHIBA) and a BVG motor supply voltage regulator on an IC901 chip. The remaining nodes of the ATS BVG are located on the main board of the video camera. The digital part of the ATS includes the microprocessor control system IC503. The BVG motor electric drive is made on the IC505 chip of the TPIC1327DF type from TEXAS INSTRUMENTS. It also contains an amplifier-signal conditioner for the phase channel sensor SAR (PG). The rotation speed sensor shaping amplifier is assembled on the IC504 chip of the KA8322QFP type from SAMSUNG.

Such a complex construction of the ACS is used to increase the efficiency of the electric drive. There are no powerful linear regulators in the IC505 chip of the electric drive system, and the rotation speed is controlled by changing the supply voltage (DRUM.VS) at pins 13, 19 of the IC505 chip, provided in the converter by the PWM method. In this way, it is possible to drastically reduce the battery energy consumption for heating the electric drive microcircuit due to only the key modes of the output transistors.

The principles of operation of digital ACS are described in more detail in [2]. However, it should be noted that in the non-contact BVG motor there are no rotor position sensors based on Hall indicator transducers, which are commonly used in most modern video recorders [3]. In our case, information about the position of the rotor is taken directly from the stator windings, for which there is an additional output from the point of their connection (COM), connected to pin 23 of the IC505 chip.

The construction of the ACS of a BB camcorder differs from similar systems of VHS format devices by the presence of a real auto-tracking system. It does not record special signals on the tape to identify the exact position of the video heads on the recording lines, so systems called AUTOTRECKING or DIGITAL TRACKING are very distantly related to real auto-tracking. The differences relate to the phase channel of the SAR explosive. If in the VHS equipment the signals from the fixed control head (CTL HEAD in [2]) serve as information for it, then in the eight-millimeter they are read by the video heads.

The pilot signal of the autotracking system (REC.PILOT) is a frequency-shift keyed message recorded in the frequency band below the transferred chrominance signal fs' in specially designated areas of the signalogram. Here, the pilot signal is spatially separated on the tape from the sections with video and audio information and does not interfere with them (in the HI-8 equipment with PCM sound, the latter coincides with the pilot signal on the tape, but there is no noticeable mutual interference in this case either).

The signal from the propeller speed sensor is fed to the pulse shaper in the IC506 electric drive microcircuit of the SANYO type LB1851M (pins 10 and 11), and from it (pin 13) to the digital part of the ACS (pins 70 and 77 of the microprocessor of the control and autoregulation system IC503). There also comes (pin 62 of the IC505 chip) an error signal from the auto-tracking system, made on the IC504 chip of the KA8322 QFD type (pin 48). The motor control signal (CAP PWM) from pin 75 of the IC503 microprocessor through pin 6 of the CN901 connector, the amplifier on the ICC902 op amp in the converter goes all the way to the same IC901 multifunction chip (pin 8). From it (pin 21), through a key regulator on transistors Q952, Q953, a low-pass filter L952C957C958, pin 7 of the CN901 connector, the signal is applied to pin 4 of the IC506 electric drive microcircuit. The instantaneous speed of the tape pull depends on the value of the voltage on it (CAP. VS).

Consequently, the converter, in addition to its main purpose, works in automatic control systems for BVG and VV engines, which must be borne in mind when performing diagnostics. For example, the use of external voltage sources DRUM.VS and CAP.VS is excluded in the chamber, since in this case the ACS feedback loops will be broken.

According to the author's observations, many malfunctions of camcorders occur due to their improper operation: at high humidity and temperature, as a result of falling (sometimes into water), ingress of foreign objects and other reasons. Often, failures occur when high or in the wrong polarity voltage is supplied from external sources, as well as unstabilized (with ripple) voltage. All of the above causes, first of all, disable the elements of the power supply systems and the electric drive of video cameras.

Before starting repair and diagnostic work, you should try to get a service manual or at least a set of circuit diagrams for the model being repaired. At the same time, there is no need for their independent drawing, which greatly simplifies the matter. However, in practice, repairs have to be carried out mainly without any documentation. In this case, the following procedure can be recommended. After disassembling the camcorder, it is necessary to locate the DC/DC CON-VERTOR. Usually they are made either in completely soldered metal cases, or the board is covered with screens on both sides. Sometimes the converters are mounted as separate units with detachable connections, sometimes they are mounted on large printed circuit boards together with other video camera units. All the same, the screens must be dismantled to ensure free access to the elements.

A very important stage is the compilation of sections of circuit diagrams related to the input and output circuits of the converter. This rather time-consuming, but, of course, useful procedure is carried out both visually (including through the light) and by dialing with needle probes. Since the conductors almost always pass from one side to the other repeatedly through a double-sided or multilayer board, you need to solder one of the ohmmeter leads to some point in the desired circuit. In this case, the board can be rotated as you like. Unfortunately, the drawing of circuits is often difficult due to the use of multilayer printed circuit boards, the lack of marking of elements, the ambiguity in their identification (it is not always possible to confidently attribute any unpackaged element to a certain type - a transistor, a diode assembly, a zener diode, etc.) .

After compiling the necessary sections of the circuits, they begin to measure the output voltages of the converter in various modes of the video camera (VCR, CAMERA). If the modes are not initiated or quickly turn off, you should ring the output circuits and power elements and make sure that there are no short circuits to the common wire. Then try to manually start the converter by opening the appropriate keys in order to detect missing output voltages (the operation of the converter is often blocked by the microprocessor even if only one voltage is missing).

It should be especially emphasized that in the presence of a short circuit in the output circuits, the camera cannot be turned on. First, the broken elements are found. Powerful and medium power transistors, microcircuits (in power circuits), filter capacitors (oxide), zener diodes, chokes, transformers and fuses (for open circuit) are subject to verification. Other elements fail much less frequently.

Let's move on to the consideration of specific cases of repair from the author's practice. The SAMSUNG - VP - U12 video camera described above fell into the water, after which it turned out to be completely inoperative. Rinsing with an alcohol-petrol mixture of the affected units did not give any effect, since the camera was in an activated state when it fell (in such cases, an urgent disconnection of the battery is necessary). The voltage converter board is connected to the main board through CN901, CN902 screw connectors, so continuity of the output circuits is not difficult. There were no short circuits. However, the blown fuse PS901 indicated a short circuit inside the converter itself. Alternately soldering the chokes L950, L907, L908 showed the presence of a breakdown of the Q914 transistor type 2SB1121 (in order to solder the leadless elements, it was necessary to make a special nozzle with a cutout for the soldering iron).

Due to the fact that imported transistors in surface-mounted packages are in short supply, it makes sense to choose affordable equivalents. Transistor 2SB1121 of SANYO pn-p structure in SC-62 package has the following parameters:

UKE max = 25V, lK max = 2A, RK max= 0,5W (without heat sink), IKB arr = 0,1 μA, h21E = 100...560, UKE us = 0,45 W, ft = 150 MHz.

It is hardly possible to pick up anything similar from domestic transistors, so the choice fell on the affordable 2SB1010 transistor from RHOM in the SC-51 package (0,5 dollars), which has close parameters. The transistor pinouts are shown in fig. 2. Since the dimensions of the 2SB1010 transistor do not allow it to be placed under the converter screen, it is required to slightly grind off its case to a thickness of 3 mm.

After replacing the transistor, the performance of the converter was restored, but the camcorder's VCR immediately pushed it back after loading the cassette. Since the BVG did not rotate during loading, the modes of the nodes and elements of the electric drive system of the BVG engine were checked. The necessary voltages and control signals supplied to the IC505 electric drive microcircuit turned out to be normal, which indicated the failure of this microcircuit. This was not surprising, since the BVG was jammed with adhesive tape. After replacing the chip, the camcorder's performance was restored.

Options for replacing transistors in the power supply systems of other camcorder models will be considered in the following publications, if possible.

Literature

1. Samokhin V. Choose Cinderella. - STEREO & VIDEO, 1997, No. 6, p. 122 - 129.
2. Petropavlovsky Yu. VHS format video equipment. Digital ATS of video cassette recorders. - Radio, 1993, No. 8, p. 5-7, No. 9, p. 16 - 18.
3. Petropavlovsky Yu. VHS format video equipment. Non-contact electric drive systems - features and repairs. - Radio, 1996, No. 1, p. 11 - 14.

Author: Yu.Petropavlovsky, Taganrog

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