Repair of Dendy game consoles: replacement of connectors and other services.
- How can we help you
- Dendy won't turn on
- No picture
- Cartridges not being read
- Joystick not working
- What to take with you?
- How much time will it take?
- What about the warranty?
- no picture
- cartridges are not read
- joysticks don't work.
- loading masters;
- availability of spare parts;
- complexity of repairs.
So, you have found your favorite childhood toy - Dendy. We decided to return to the carefree past, but the set-top box did not turn on, or other problems arose:
Do not worry, all these problems can be solved in our service center. Bring your dandy to us and we will return your happy childhood!
Sometimes, to bring the old prefix back to life, it is enough to disassemble it and clean it from dust. Or tidy up contacts that have oxidized or moved away.
Of course, the dandy may not be included for more serious reasons. The most common of these is the burnout of the power supply due to power surges. In this case, our specialists will replace the burnt components with new ones.
All these procedures will take no more than an hour. Contact.
If there is no image at all, or the picture jumps, ripples, disappears, then the connection cable to the TV is damaged, or the Dendy video connector is faulty.
Contact our service center with these problems and we will replace the broken connector.
Most likely, the connector for cartridges is damaged (this is a fairly common breakdown of Dendy). For example, dust has accumulated in it, or foreign objects have got into it.
If your set-top box cannot read any of the cartridges, bring the dandy to us, the masters will clean or repair the cartridge slot, and if necessary, replace it with a new one.
Most often, a problem with a gamepad occurs due to damage to the connection connector. In this case, bring your dandy to us along with joysticks, we will find out what the problem is and fix it.
Before going to our service center, call us by phone to clarify which wires and accessories you need to bring along with the attachment for diagnostics and repair.
The time it takes to repair your console is determined by several factors:
The operator will tell you the approximate time by phone if you describe your problem to him in sufficient detail.
Everything without Dendy game console repair work in our workshops is guaranteed.
The warranty period depends on the type of repair performed.
Legendary Dendy
Varieties of consoles Dendy
Dendy is a legendary game console released by Steepler in 1992. The most popular prefix of the nineties in Russia. Dandy was a pirate clone of the NES console and was sold only in the CIS. It is unknown in other countries.
Dandy was produced in several versions:
- Dendy Classic had two video outputs and two switchable joysticks, which were attached to the sides of the console.
- Dendy Classic II had a more rounded shape, reminiscent of modern consoles.
- notable for the fact that it was possible to buy a light gun to it and connect it instead of the second gamepad.
- features non-detachable gamepads. The gun was connected to a special connector in front of the console.
- . The gun is included!
- . The prefix, joysticks and gun are black (previous versions are white and gray).
Modern Dendy
8-bit consoles, clones of the very first Nintendo are being released even now. They are made in China and Taiwan. The sellers of these consoles in Russia often call them "dandies", but these crafts have nothing to do with Steepler. The release of "real" dandies was discontinued in 1996.
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tags: dendy repair, dandy console repair
1.3. circuit diagram
This section provides detailed schematic diagrams of the processor module and consoles, and also considers the option of building a cartridge with software for 8-bit DENDY game consoles.
1.3.1. processor module
There are usually three boards in the DENDY game console:
* central processor;
* output connectors;
* RF modulator and stabilizer.
The boards are interconnected by flexible flat (ribbon) cables. Sometimes there are options made on one or two printed circuit boards, but this does not affect the set-top box circuit.
Initially, game consoles contained several chips of varying degrees of integration, with the main chips being the central processor and video processor.
The development of microelectronics has led to the fact that game consoles now include only LSI of the UM6561 type or its equivalent. In this microcircuit, the central and graphic processors, memory and I / O registers are located on one chip.
Many Korean-made video set-top boxes use several chips (usually two or three) instead of one UM6561. However, the principle of operation of the set-top box and the signals at the output connectors in this case do not change, so these circuit options will not be considered here.
Multi-chip variant
A schematic diagram of the first version of the DENDY game console, made using several microcircuits of various degrees of integration, is shown in fig. 1.12.
So, the basis of the game console is the central processor chip (IC1). The processor operation is synchronized by an external clock pulse generator made on transistors Q1 and Q2, the frequency of which is stabilized by X1 quartz (21.251465 MHz).
The signals of all internal buses (addresses A0 - A15, data DO - D7 and control) of the game console are output to the XS1 connector, to which the cartridge is connected. The data bus (pins IC1/21-28), address (pins IC1/4-19) and control (pins IC1/31,34) connect the CPU (IC1) to the RAM chip (IC3) and the video processor (IC2).
The address decoder on the 74LS139 chip (IC8) generates signals that allow other chips to communicate with the central processor. The three most significant bits of the address bus A13 - A15 (pins IC8 / 2,3,13) and the signal M2 (pin IC8 / 14) are fed to the decoder inputs. If the processor is working with the memory installed in the cartridge, then the OT signal at pin IC8/9 is low. When data is exchanged with the built-in RAM of the set-top box (IC3), a low level is received by the AO signal at pin IC8/4. A low level signal at pin IC8/5 indicates that the CPU is using the video processor chip IC2.
On the same chip with the central processor, there is also a game console sound processor and an I / O port address decoder circuit.
The output signals of the first and second audio channels are mixed and fed to the AU1 output (IC1 / 1 output), and the signals of the remaining channels - to the AU2 output (IC1 / 2 output). The complete sound signal is formed by mixing in a circuit made on resistors R8 - R12 and capacitor C7, and then fed to the output connector of the game console and to the input of the modulator that generates the RF signal.
Three digits of the number (D0, D1 and D2) written to port 4016h are transmitted to the outputs of IC1 / 39-37.
Each time the processor reads from port address 4016h, a low-level pulse appears at the CK1 output (pin IC1 / 36). And if the processor reads from port with address 4017h, a similar pulse is generated at the output of CK2 (pin IC1 / 35).
The output signals of the game consoles and the light gun are transmitted to the data bus through two buffer registers IC6 and IC7 (type 74HC368).
The video processor chip IC2, together with the video memory chip IC4, provides a full
video signal. IC2 and IC4 are connected by address, data and control buses. The IC4 video memory chip is similar to the main RAM chip.
Please note that in video processor IC2, the same pins (IC2/31-37) are used as the data bus and as the address bus. First, the lower eight bits of the address of the video memory cell come here. When a low level signal appears at the ALE output (pin IC2 / 39), this data is stored in the buffer register IC5 (74LS373). The ALE output is then set high, the IC2/26-30 pins are left with the MSBs of the address, and the IC2/31-37 pins are used as the data bus.
Video processor bus signals are also routed to the XS1 cartridge connector.
The full video signal from the VIDEO OUT output of the video processor (pin IC2 / 21) goes through the emitter follower, made on the transistor Q3, to the VIDEO OUT output connector and to the modulator.
The video signal amplification stage may be absent in some models.
Now we will briefly talk about the main differences from the basic scheme that are present in other models. All of them relate to the connectors used and the purpose of individual pins.
There are two main design options for the considered gaming system. The NES is equipped with a 72-pin cartridge connector, a 48-pin expansion connector, and 7-pin connectors for connecting game consoles. The FAMICOM (DENDY) game console is fully software compatible with the NES, but uses a 60-pin cartridge connector, a 15-pin expansion connector, and 9-pin connectors for game consoles.
The layout of all connectors of the DENDY game console is shown in fig. 1.13a-c, and NES consoles - in fig. 1.13g-e.
Single chip option
A schematic diagram of a single-chip version of the DENDY game console is shown in fig. 1.14.
Here, the functions of the central processor, video processor and memory are performed by one LSI of the UM6561 type. The frequency of the internal clock generator is stabilized by an XI quartz resonator (26.601712 MHz). Sometimes the clock generator circuit also contains a transistor.
Most output signals go directly to the XS4 cartridge connector. Part of the signals goes to the connectors for connecting game consoles XS1, XS2 and the expansion connector XS3.
Video and audio signals are transmitted to the output connectors of the game console and to the input of the modulator, sometimes through transistor amplifiers.
Output connectors
The DENDY console has two or three connectors for connecting remotes, a light gun and other peripherals. Connectors can be of three types: 7-, 9- and 15-pin.
Game consoles are allowed to be connected to the 7-1 or 9-pin console connector or to the 15-pin console expansion connector, the light gun - only to the 7- or 15-pin connector, other devices - to the 15-pin connector.
Two 9-pin connectors and one 15-pin expansion connector are used to connect the consoles. The DENDY cartridge uses a 60-pin connector on the top.
The NES has two 7-pin connectors and one 48-pin expansion connector for game controllers.
To connect the cartridge to the NES, a 72-pin connector is used, which differs from the 60-pin connector in the presence of additional circuits connected to the expansion connector. The video processor and CPU bus signals are output to this connector.
The appearance of the connectors of the DENDY game console and the purpose of individual contacts are shown in fig. 1.13. The expansion connector (Fig. 1.136) is discussed below, since it is he who is most
Convenient for connecting various additional devices.
Pin 2 (AUDIO IN) receives the audio signal, which is mixed with the output signals of the sound processor.
Contacts 4-8 (J2 DO - J2 D4) are the inputs of the corresponding bits of the port of the second joystick. Signal codes from these inputs can be obtained from port 4017h with the LDA $4017 command.
Input J1 D1 (pin 13) is connected to bit D1 of port 4016h.
When the CPU accesses ports with addresses 4016h and 4017h, short-term low-level pulses are generated at the outputs CLK1 (pin 14) and CLK2 (pin 9). The outputs OUT0 -OUT2 (pins 10-12) receive bits DO -D2 of the word written to port 4 016h.
The IRQ input (pin 3) receives an interrupt request signal.
1.3.2. Cartridge
The replaceable module of the DENDY game console - a cartridge - usually contains two ROM or RAM chips.
One ROM chip is connected to the video processor and stores character generator information. Instead of character generator ROM, some cartridges use a static RAM chip. Another ROM chip with software is connected to the central processing unit. Sometimes there is an additional lithium battery-powered RAM on the cartridge board, which is designed to save the game situation.
Almost all cartridges, with the exception of the simplest ones, have a memory page controller chip that acts as a programmable address decoder.
Structurally, the DENDY prefix cartridge is a protective plastic case measuring 105x90x20 mm with a key in the form of two bevels for proper installation. It houses a printed circuit board with a 60-pin connector and installed unpackaged microcircuits: ROM, RAM and a page controller.
A schematic diagram of a game cartridge without additional RAM with an MBC1 page controller is shown in fig. 1.15.
The cartridge consists of two ROM chips (IC1 and IC2) and a memory page controller IC3. Chip IC1 (27С128) is the ROM of the video processor! with character generators written in it.
In the address space of the video processor, individual pages of the ROM are placed at addresses 0000h - 1FFFh. The least significant bits of the address are fed to the IC1 chip directly from the corresponding pins of the XS1 connector. senior ranks
Rice. 1.15. DENDY Game Console Cartridge Schematic Diagram
addresses VA12 and VA13 are generated by the memory page controller chip IC3.
The ROM chip is selected when there is a low-level signal at the CS input (pin IC1 / 20) connected to the VA13 line of the video processor address bus. Data is transferred from the ROM outputs to the pins of the XS1 connector.
Chip IC2 (KONAMI ROM 1Mbit) is a masked ROM with a program recorded in it with a capacity of 1 Mbit (128 Kb). The low bits of the address A0 - A13 come from the corresponding contacts of the cartridge, and the high bits of the address A14 - A16 are generated by the memory page controller IC3. The CS signal, which enables the operation of ROM IC2, is also transmitted from IC3.
IC3 is a programmable address decoder that generates the MSBs of the address for ROM chips IC1 and IC2. It also generates a VA10" signal, the level of which determines the choice of screen display mode.
In the cartridge under consideration, some of the outputs are not connected, so the capabilities of the microcircuit are not fully used.
1.3.3. Modulator
The DENDY game console modulator receives an image signal from the IC2 video processor chip and an audio signal from the IC1 central processor chip and generates a full TV RF signal in one of the meter ranges. The modulator circuit is not standardized and is usually determined by the manufacturer. However, the principle of operation and the composition of the main components are always the same, so changes in the circuit should not cause difficulties during repairs.
A schematic diagram of one of the possible variants of the RF modulator is shown in fig. 1.16.
The master RF oscillator is made on a high-frequency transistor Q2 (analogous to the transistor
KT368A). It forms the carrier frequency of one of the television channels. Typically, the operating frequency of the set-top box generator is in the range of 170-230 MHz and is determined by the elements L1, C8 - C11 1, R9 - R11. The frequency is adjusted by changing the inductance of the coil L1.
The generator, implemented on the transistor Q1 (analogous to the transistor KT3102), forms the audio subcarrier for the full television signal. The output signal of the generator is modulated by an audio signal coming through the R4, C1 circuit from the AUDIO IN input (pin 4 of the CN1 connector).
Depending on the manufacturer of the set-top box, the generator frequency is 5.5 or 6.5 MHz. Fine tuning of the signal frequency is carried out by rotating the core of the transformer T1.
The mixer, made on diodes D1, D2 (analogous to the KD503A diode), transformer T2 and transistor Q3, forms a full HF television signal. The mixer input receives a master oscillator signal and a low-frequency video signal from pin 3 of the CN1 connector. From the output of the mixer, the RF signal is transmitted through the matching circuit C15, L3 to the RF OUT output connector of the processor module.
1.3.4. Game consoles
There are about ten different types of game consoles for the DENDY game console. However, the most widely used is the standard game console included in the delivery set, the turbo remote with additional buttons and the light gun.
Below are the schematic diagrams of these devices, as well as the adapter diagram for the simultaneous connection of four consoles.
Standard game pad
The standard game console for the DENDY console consists of a movable cross and four
individual buttons. Inside the remote control there is an unpackaged shift register microcircuit, which is an analogue of the HEF4021B microcircuit. In the absence of the original microcircuit, almost any 8-bit shift register can be used.
A schematic diagram of a standard console is shown in fig. 1.17.
Rice. 1.17. Schematic diagram of a standard game console for the DENDY console
When a button is pressed while playing, the corresponding input of the shift register is driven low. A high level when the buttons are open is provided by connecting the input lines of the register to the +5 V power bus through resistors with a resistance of 10-68 kOhm.
The states of the inputs in the IC1 register are stored when a high-level pulse arrives at the PE input of the microcircuit. After that, on the negative edge of the signal at the input CLK (output IC1 / 10), the contents of the register are shifted and the most significant bit is output on the D0 bus
The second game console supplied with the set-top box may not have the START and SELECT buttons, but this does not affect the scheme of the console and the principle of its operation.
Turbo Remote
Schematic diagram of the turbo remote control for the DENDY game console is shown in fig. 1.18.
The only difference between the turbo remote control and the standard one is the presence of an additional T6 Hz output on the shift register microcircuit and two additional buttons TURBO A and TURBO B connected to this output.
The internal generator of the remote control chip generates a sequence of pulses with a frequency of 6-10 Hz at the output T. Thus, pressing and holding TURBO button A is the same as pressing and releasing button A at an intensity of 6 times per second. The use of these buttons reduces wear on the remote keys, since the A and B buttons are usually used in the game when shooting.
Rice. 1.18. Schematic diagram of the turbo remote control for the game console DENDY
Adapter for connecting four remote controls
Some games can have up to four players. In this case, four game consoles are connected in parallel to the connectors of the game console through a special adapter.
Schematic diagram of the adapter is shown in fig. 1.19.
As can be seen from the schematic diagram, the main task of the adapter is to ensure that information is read from consoles 1 and 3 during the first eight clock pulses, and from consoles 2 and 4 - with the next eight.
The synchronization signal applied on the STRB line fixes the state of the consoles in their internal registers and performs the initial setting of the adapter circuits.
During the first eight clock pulses, the Q8 outputs of counters IC1 and IC2 are driven low, which ensures that clock pulses are sent to consoles 1 and 3, as well as the information from these consoles is transmitted to the inputs of the game console.
After the eighth clock sent from the game console when reading from the I / O port, the Q8 output of the corresponding chip (IC1 or IC2) goes high (log. 1), which causes the switch IC3 or IC4 to switch and connect to the console connectors consoles 2 or 4 respectively.
light gun
On fig. 1.20 shows the possible options for the circuit diagram of the light gun of the DENDY game console.
A phototransistor is used here as a photosensitive element. In the cheapest set-top boxes, it is sometimes replaced by a photodiode, which leads to a deterioration in the sensitivity of the device.
The signal from the output of the photodiode through the decoupling capacitor C1 is fed to an amplifier made on the transistor Q1. From the collector of this transistor, the inverted signal is transmitted through pin 5 along the D4 circuit to the processor module of the game console.
If the gun is pointed at the television screen, then a pulse signal is generated at the D4 output with a frequency equal to the frame scanning period.
The trigger of the light gun is connected to a button with normally closed contacts. When the trigger is released, the D3 connector pin is connected to ground. When the trigger is pressed, the contacts open and a high logic level signal appears at the D3 input, which is provided by connecting this circuit inside the game console through a 10-51 kΩ resistor to the +5 V bus.
1.3.5. Power Supply
The DENDY game console power supply consists of an external AC adapter and an internal stabilizer.
The task of the external network adapter is to convert the mains voltage ~ 220 V into a constant voltage of 9-12 V, which is transmitted to the internal stabilizer of the game console.
Schematic diagram of the DENDY network adapter is shown in fig. 1.21.
When repairing the unit, remember that the central contact on the output connector is connected to a common wire.
The unstabilized voltage from the adapter is supplied to the internal stabilizer of the game console, made on the AN7805 chip or on a transistor and located in the processor module. A constant voltage of +5 V is formed at the output of the stabilizer.
Schematic diagrams of two variants of the DENDY game console supply voltage stabilizer are shown in fig. 1.22 and do not need additional description.
Rice. 1.22. Schematic diagrams of the voltage regulator for the game console DENDY
1.4. Typical malfunctions
Attachment does not turn on
Possible reasons: malfunction of the network adapter or internal stabilizer; short circuit or open supply circuits; cartridge malfunction; processor module failure.
1. Measure the output voltage of the network adapter. If it exceeds 9-12 V, replace the mains
adapter. Practice shows that most often failures are caused by rectifier bridge diodes. If the transformer fails, any power supply with an output voltage of 9-12 V and a permissible load current of 500 mA will do.
2. Disconnect the remotes, cartridge and modulator from the processor module, then check the game console units for short circuits. If a short circuit is detected, after eliminating it, check the stabilizer and the low-resistance resistor installed in it. When an overload occurs, one of the printed conductors in the power circuit usually breaks, so you need to carefully inspect the boards to make sure that the conductors are intact.
H. If there is no short circuit, check the internal stabilizer of the game console. The voltage at the output of the stabilizer must be within 5 ± 0.1 V; otherwise, in the stabilizer, made on the AN7805 chip, you should replace the IC1 chip (similar to KR142E-H5A) and check the capacitors C1 - C4. In a stabilizer implemented on a transistor, check transistor Q1 (possible replacement - KT815), zener diode D1 (possible replacement - KS156A) and resistor R1. Instead of a resistor, it is permissible to put a fuse that will protect the stabilizer from a short circuit.
4. Turn on the set-top box without remotes, modulator and cartridge. A video signal must be present at the VIDEO OUT jack. When this signal is applied to the LF input of the TV, a chaotic image will appear on the screen, consisting of colored dots and squares. The presence of an output signal indicates a malfunction in the consoles or in the modulator.
5. If there is no output signal, check the crystal oscillator and the transistor video amplification stage. The serviceability of the quartz resonator X1 and transistors Q1 - Q3 allows us to conclude that it is necessary to replace the entire processor module.
The device is unstable
Possible reasons: malfunction of the external network adapter or internal stabilizer; contamination of the contacts of the cartridge connection connector.
1. Check the output voltage of the AC adapter. Often a failure occurs due to the low load capacity of the adapter supplied with the game console. The problem is solved by connecting a more powerful adapter.
2. Check the reliability of the contact connections in the connectors of the set-top box. The cartridge connection connector must be inspected especially carefully. Wipe contacts with alcohol.
3. Check the internal stabilizer of the game console. It is useful to install a microcircuit or a power transistor of the stabilizer on a radiator with a sufficient dissipation area (about 10 cm2).
4. Install additional capacitors in the power circuit, for example, with a nominal value of 100.0 uF x 16 V and 0.01 uF on each of the prefix boards and in the cartridge.
Light gun not working
Possible reasons: a break in the connecting cable or bad contacts in the connector; malfunction of the photodiode or transistor of the light gun; malfunction of the trigger contacts in the light gun.
Troubleshooting algorithm:
2. Check the transistor in the light gun and the contacts under the trigger. Make sure that there is a contact closure when the trigger is pressed, since failure, as a rule, occurs in the mechanical part of the gun.
3. The low sensitivity of the gun is often due to the displacement of the focusing lens installed in the barrel. In this case, you need to install the lens in place and secure it. Adjusting the lens mount allows you to improve the performance of even a working light gun.
4. If the internal circuits of the light gun are working properly, the entire processor module of the game console needs to be replaced.
Remote control not working
Possible causes: break in the connecting cable or poor contact in the connector; buttons dirty; remote control chip failure.
Troubleshooting algorithm:
1. Check the integrity of the connecting cable and the reliability of the connection in the connector. In case of failure of the connector, replace it, together with the mating part, with any 7-pin connector that is available.
2. Check the input signals PE and STROBE. The absence of signals indicates the need to replace the central processor.
3. Check the output signal of the microcircuit installed in the remote control. If there is no signal, replace the remote control.
Some buttons on the remote do not work
Possible causes: contamination of the remote control or a malfunction of the microcircuit.
Troubleshooting algorithm:
1. Wipe the remote control board and the rubber gasket with conductive pads with alcohol.
2. If the conductive pads on the rubber gasket are faulty, repair them by gluing pieces of foil. It is more convenient to use foil from cigarette packs: it has a paper base, which provides better adhesion to rubber.
3. In case of damage to the conductive coating on the board, restore it using a cleaned mounting wire soldered to the tracks of the printed circuit board.
4. If all contact pads are in good order, it is necessary to replace the microcircuit installed in the remote control, or the entire remote control.
No RF signal at modulator output
Possible causes: violation of the generator settings, a malfunction of the master oscillator or mixer.
Troubleshooting algorithm:
1. Verify that the failed element is in the RF modulator circuit by checking for video audio signals at the LF output. The absence of any of these signals indicates a breakdown of the processor module.
2. If there is no sound or picture, the oscillator is most likely defective. To check the generator, you should measure the frequency of the output signal: it should be in the range of 170-230 MHz. The absence of a signal leads to the conclusion that the transistor Q2 needs to be replaced. If the generator frequency goes beyond the specified limits, it is necessary to check the elements LI, C8 -C11, R10, R11.
3. After making sure that the master oscillator is working, check the mixer (diodes D1, D2 and transformer T2), as well as the matching circuit L2. C13, C14.
4. The absence of an audio signal with a normal picture indicates a failure of the audio sub-carrier generator. In this case, check that the frequency of the IF sound generator matches the television standard (5.5 or 6.5 MHz) and, if necessary, adjust the generator by rotating the core of the transformer T1. If there is no signal at the output of the generator, replace transistor Q1.
In this section, the architecture of the DENDY game console is considered from the point of view of programming, the central processing unit, imaging methods, and the operation of the audio processor are described in detail. Particular attention is paid to the internal registers of the game console and software features.
The block diagram of the DENDY game console is shown in the figure.
The heart of the console is the central processing unit (CPU). All NES-compatible set-top boxes use a processor similar to the well-known 6502 microprocessor.
A music coprocessor is placed on the same crystal as the central one. The original set-top box manufactured by NINTENDO uses an audio processor that implements four analog and one digital sound channels. However, most set-top boxes supplied to Russia are Korean analogues, they have an integrated audio coprocessor without a digital channel.
The Direct Memory Access (DMA) controller is also located on the CPU chip.
Game consoles and other devices are connected to the data bus through an input / output module, which is two buffer registers.
2 KB RAM is also allocated to an independent block, which is intended for storing variables, game data, the processor stack, etc.
The formation of the picture on the TV screen is provided by the video processor of the set-top box (PPU). Image information is stored in video memory (VRAM) with a capacity of 2 KB. This memory is not connected to the main memory of the set-top box, it is accessed only through the PPU registers. The video processor generates a standard video signal, which is fed to the output connector of the set-top box.
The modulator located in the housing converts the image and sound signals into an RF signal intended for feeding to the antenna input of the TV.
The consoles have control buttons and an interface chip that transmits a data byte to the central processor of the set-top box.
The cartridge, which connects to the set-top box via a 60-pin (or 72-pin in the NES model) connector, contains a 16 to 256 KB read-only memory, which contains the game program, and video processor memory.
Battery-powered random access memory (SRAM), where the game situation is recorded at the time the console is turned off, can also be located in the cartridge. Some cartridges include optional ROM or Video Processor RAM (VRAM/VROM) to make full use of the GPU's resources.
If the ROM capacity of the cartridge exceeds 32 KB, then its mandatory part is the memory page controller (MBC), which switches the pages used by the central processor.
The supply voltage (+5 V) for the set-top box comes from the mains adapter through the built-in stabilizer.
Many have at home game consoles for the TV set of the DENDY family or similar. We can assume that you are lucky if your set-top box was assembled in Taiwan, but most often they come to our country from China, where it is not customary to care about the quality of goods, which is the reason for the bulk of the malfunctions. And the child does not always handle his next toy neatly. It is no coincidence that manufacturers themselves do not give guarantees for a period of more than 6 months.
If problems arise, you won’t have to look for a repair shop every time if you know how to hold a soldering iron in your hands and use my repair experience.
It can be immediately noted that repairing video set-top boxes for a TV, as a rule, does not require an electrical circuit and in-depth knowledge of radio electronics. Enough and the volume of the school curriculum.
All the most common malfunctions can be divided into three conditional groups (they are listed in order of probability of occurrence). This implies that the game cartridge itself is working, which is easy to verify by turning it on on another console.
1. The computer turns on and shows the game menu, but the joystick does not work
Most often this is due to the fact that the connecting wires from the joystick to the computer are connected through a connector, and in the connector they are connected not by soldering, but by clamping and eventually oxidize in this place, which breaks the electrical contact. The connector itself is not collapsible and its design does not provide a quality connection.
You can verify the presence of contact using a tester by opening the disconnected joystick and ringing the circuits of five wires in the cable from the joystick to the connector (Fig. 7.8).
Some joysticks are connected to the game console through a terminal block located inside the console case. A break in one of the wires in the cable from the joystick to the set-top box in this case may be in the place where the cable is often kinked, i.e., near the body of the game console.
The easiest way to troubleshoot these problems is to replace the cable or shorten it and solder the wires directly to the corresponding pins of the connector on the PCB of the set-top box.
Sometimes there are defects in printed conductors (breaks) suitable for joystick connectors. This is due to poor mechanical fastening of the connectors themselves to the PCB.
Another cause of some joystick buttons not working can be found by looking at the plastic inserts under the joystick push buttons. If there is damage, they must be replaced.
The last reason why the joystick may not work is damage to the microcircuit on the board of the joystick itself (it is filled with brown compound). In this case, it is better to buy a new joystick, since it is not advisable to repair it.
2. The computer does not turn on! It is necessary to check the operability of the power supply, for which we measure the tester with a constant voltage of 14 ± 2 V at the contacts of the plug (Fig. 7.9). When measuring, it is necessary to connect an eq to the contacts of the plug.
vivalent load (about 51 ohms). If the voltage is less than 9 V, this is a sign that one of the rectifier bridge diodes is not working. It will need to be replaced.
Most often, the malfunction is associated with a broken contact in the wire near the plug that connects to the set-top box. It is easy to check the wires with a tester and, in case of a break, replace them together with the plug. You can do without a plug by soldering the wires to the corresponding circuits on the printed circuit board of the set-top box.
3. The computer turns on, but sometimes it spontaneously resets during the game or behaves in another incomprehensible way
The reason for this type of malfunction may be poor-quality soldering of the main printed circuit board with microcircuits inside the video set-top box,
First of all, it is necessary to inspect and check the quality of the connections at the soldering points of the voltage regulator microcircuit. This chip has the appearance shown in Fig. 7.10, and a metal heat sink plate is fixed on it. On the board, as a rule, this microcircuit is located not far from the power connection socket. Due to the lack of a rigid fastening of the heat sink, in the place where the microcircuit is soldered, the printed conductor sometimes cracks and breaks, or the microcircuit hangs in the holes - cold soldering.
Poor soldering and cracks in printed conductors can also be in other places on the board (for example, near connectors). Without a magnifying glass, such defects can be difficult to detect.
To eliminate suspicious places, they must be carefully soldered with a low-power (16 ... 30 W) soldering iron using rosin as a flux. A good solder should have a mirror finish. We remove the remains of rosin from the board with a rag soaked in alcohol or acetone.
The microcircuits themselves and other components are mainly used in Japan, they are highly reliable and rarely fail.
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