Dendy: selection, operation, repair. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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The author of the proposed article has rich experience in operating game consoles and even organized the rental of cartridges for them. He tells readers about the problems they most often face and how to solve them.

SELECTION OF SUPPLIER

When you go out to buy a Dendy or similar TV game console, rent or buy a cartridge with the longest and most graphic game (for example, "Prince of Persia"), or better yet, a cartridge containing four games, among which is the one mentioned. It will not fit all consoles - many of them will not have enough RAM. Naturally, you should buy the one on which all games work.

Look out for consoles like the "Dendy-Junior" with "wide" joystick slots in the front of the case. They have a number of advantages: all parts are installed on one, not on three boards, which eliminates the possibility of breaking the wires connecting the boards; the high-frequency unit is carefully shielded, which reduces the radio interference created by the set-top box; more advanced processor and other components have been used, which have improved image quality and reliability.

The "Kenga" prefix, which fits entirely in the joystick, is very promising. Even those cartridges that do not start at all on other consoles often work perfectly with it. Unfortunately, it has a significant drawback in our conditions - it cannot be repaired if it breaks down.

An important advantage of the "Nintendo" set-top box over other eight-bit ones is the built-in ROM with simple games, which allows you to use it without connecting a cartridge. When you install it, the ROM will automatically turn off.

OPERATION OF SUPPLIERS AND CARTRIDGES

Never insert or remove a cartridge while the power is on - this may lead to its or the entire set-top box failure! The set-top box should be turned off using the switch intended for this, and not by pulling out the plug of the power supply connected to the network. Do not press the joystick buttons and the "RESET" button on the console at the same time - this may damage the joystick.

Extreme temperatures are dangerous for the set-top box and cartridges, so keep them away from frost and direct sunlight. Keep them away from water, acetone or gasoline. Contaminated connector contacts can only be wiped with pure alcohol, but in no case with alcoholic drinks or cologne - they leave behind a hard-to-remove plaque. Do not bring the contacts to the point where the accumulated dirt can only be removed with a knife or sandpaper. Such cleaning inevitably damages the protective layer on them, as a result of which the oxidation process only accelerates.

Pictures on the body of the cartridges are easy to scratch, and after prolonged use they are erased. This will not happen if you protect them with adhesive tape ("adhesive tape") of sufficient width. Try to buy small-sized cartridges. Experience shows that they are mechanically stronger.

CARTRIDGE FAULTS

Suppose all the rules were followed, but the cartridge stopped working and cleaning the contacts does not help. If the prefix is ​​working (this is checked by installing another cartridge), then try pressing the "RESET" button several times - sometimes this gives a positive result.

It happens that a cartridge that does not create any problems on other set-top boxes "does not want to work" on yours. Some set-top boxes can be made less critical to its parameters by connecting a 10 pF capacitor in parallel with the quartz resonator located on the processor board. But more often the reason lies elsewhere - the deviations of the dimensions of the cartridge parts (most often the board) from the nominal ones are too large (this happens if it is manufactured by a "pirate" company) or the stops fixing its board in the case are damaged. As a result, some pins of the "CARTRIDGE" socket do not connect to the corresponding pads on the board.

To fix the defect, remove the case from the set-top box, and the front cover from the cartridge and insert it into the socket. Make sure that the contacts of the board and the socket are aligned and that there are no gaps between them (Fig. 1). The correct position must be fixed by placing spacers 1 or 2 (or both 2 and 3) and stops 6, 3 of a suitable size from any insulating material between the cartridge body 6 (Fig. 4) and its board 5 and fixing them with glue. If the PCB is too thin, use a soldering iron to apply some solder to its pads. But do not overdo it - too thick a layer can damage the socket contacts. Close the repaired cartridge with a lid and, after inserting and removing it several times, make sure that the contact is reliable.

It happens that the cartridge does not fully enter the socket due to the fact that it rests against the ejector lever available in the prefix. Try to file its body a little at the stops, and if there are a lot of such cartridges, after disassembling the prefix, file the ends of the ejector.

Some players in a hurry or inaccurately insert the cartridge into the console "back to front" (turned 180 °). This often leads to the failure of both devices. You can protect them with a low-power diode of any type (better than germanium, for example, the D9 series with any letter index). It is included in the break of the printed conductor of the +5 V power circuit on the cartridge board (Fig. 3). The conductor is cut at any point from the contact of the connector to the first of the elements of the device connected to it. In cases where the power circuit is duplicated on the other side of the board, the second conductor will also have to be cut.

Sometimes during the game, the image on the screen freezes and does not respond to manipulations with the joystick. You have to restart the console by turning the power off and on again. An oxide capacitor with a capacity of 4,7 ... 47 μF with a nominal voltage of at least 6,3 V often helps to get rid of "freezes", connected between the cartridge power buses in accordance with Fig. 4.

POWER SUPPLY FAULTS

Often the reason for the inoperability of the set-top box is in the power circuits. Therefore, when turning it on, first of all check if the LED indicator is on. If not, make sure that the power supply (AC adapter) is connected correctly and securely and measure the voltage at the contacts of its plug with a voltmeter. The unit disconnected from the set-top box should have about 14 V, and the unit connected to it should have at least 9 V. The failure of the adapter is quite likely, since it gets very hot during prolonged operation. Failure analysis showed that in 90% of cases the cause of overheating is too high leakage current of the filter oxide capacitor. Its replacement with a serviceable one will reduce the temperature of the block and increase reliability.

If necessary, the game console can be powered by power supplies designed for radios. Suitable are those that give a stabilized voltage of 6 V at a current of at least 0,1 A. To increase the output voltage, the internal regulator of the unit must be turned off, for which the conductors going to the output plug are connected directly to the diode bridge, as shown in fig. 5. Do not forget that the negative pole of the rectifier must be connected to the center pin.

Fig. 5

In order for the plug intended for connection to the radio to fit into the socket of the set-top box, its plastic part should be sawn off with a file. Sometimes, as a result of prolonged use, the contact is broken in this particular socket. Of course, you can replace it with a new one, but the old one will still work if you bend the contact plate in it with an awl.

If the power supply is working, but the set-top box still does not work and the LED on it does not light up, the +5 V voltage regulator chip located on the processor board is almost certainly out of order. It can be replaced with a similar domestic KR142EN5A or KR142EN5V. In the event that a heat sink is not provided for the microcircuit (manufacturers do not save on anything!), it must be installed.

JOYSTICK FAULTS

First, check with an ohmmeter the integrity of the wires of the cable connecting the joystick to the console. Fig. will help to do this. 6.

If a break is detected, it is enough to eliminate it - and the joystick will work. First of all, try to find the place of the cliff. As a rule, the wires break near the contact pads of the board in places of frequent kinks. The faulty part of the cable can be cut off and, after stripping the wires of the good one, solder them to the appropriate sites. If it was not possible to find the place of the break or the serviceable part of the cable is too short, it remains to cut off the insulation at the corresponding contact of the connector, exposing its tail part, and solder a piece of insulated wire of a suitable length instead of the broken one. Fill the place of soldering with sealant or glue, and attach the additional wire to the cable with insulating tape.

If the cables and connector are working, it will be quite difficult to repair the joystick. Some recommendations on this subject are in the article by S. Ryumik "Features of the circuitry of eight-bit video set-top boxes" ("Radio", 1997, No. 10, pp. 27-30; No. 12, pp. 20-23).

Joystick connectors (especially "narrow" connectors) are very unreliable; contact in them is broken during prolonged use. Of course, if the joysticks are never disconnected, the connectors will last longer, but the set-top box in this state cannot be hidden in a box. I recommend installing in parallel with the existing ones any more reliable small-sized multi-pin connectors (for example, RSh2NP-1-30). Their counterparts should replace the sockets on the joystick cables. When this is not desirable, limit yourself to making an adapter from the old connector to the new one.

HOW TO GET RID OF RADIO INTERFERENCE CAUSED BY THE SET-TO-BOX

Many owners of "Dendy" consoles notice that during the game they create strong interference with household radio equipment, especially TVs powered by indoor or surrogate antennas. This is due to the fact that the carrier frequency of the set-top box signal is in the range reserved for television broadcasting, and it itself contains many parasitic harmonic and combinational components. Of course, it would be possible to provide filters that reduce the power of interference to an acceptable value, but this would significantly increase the cost of video set-top boxes.

The best solution in this situation (which, by the way, improves the image quality) is not to use the high-frequency ("RF") output of the set-top box, connecting it to the low-frequency inputs of the TV ("VCR" or "AUDIO / VIDEO" connectors). To do this, the set-top box provides outputs "AUDIO" and "VIDEO". Try connecting them to your TV with a VCR cable.

Do not be upset if the image and sound do not appear. It is possible that these connectors are simply not connected in your set-top box. But the necessary signals are definitely there - they are fed from the processor board to the high-frequency unit. Four wires go to it: common, with +5 V supply voltage and image and sound signals. Usually the pads to which they are soldered have corresponding inscriptions. If they are not there, you can find the video output by connecting the central contact of the "VIDEO" connector (previously unsoldering the conductor going to it) in turn, until an image appears, from each of the sites through an oxide capacitor with a capacity of at least 10 microfarads. The negative terminal of the capacitor must be connected to the connector. The sound signal is found in the same way. It happens that at the input of the high-frequency unit it is too weak. Then try experimentally to find a circuit on the processor board in which its amplitude is sufficient.

If the set-top box, even when connected to the TV at a low frequency, still creates interference, it is necessary to turn off its high-frequency unit by cutting the printed conductor through which the supply voltage is supplied to it.

Author: V. Utkin, Zlatoust, Chelyabinsk Region

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