Repair of cordless phones. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Telephony

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Modern cordless telephones (in everyday life they are often called radiotelephones) have settled in offices and many of our apartments for a long time. What kind of devices you will not meet - for every color and taste. But here's the problem - they fail more often than ordinary (disk) ones. What are the reasons and what are the methods of repairing cordless phones, says the author of this article.

Radiotelephones, no doubt, have a lot of advantages. However, they also have many disadvantages. The advantages include, in particular, the absence of a connecting wire, which allows you to talk at a distance of up to two kilometers from the base unit for phones operating in the 900 MHz band and up to 200 meters for phones operating in the 20 ... 49 range MHz. As for the disadvantages, one of them is the dependence on the power supply. In the absence of mains voltage (i.e., if your electricity is turned off), you will not be able to use the radiotelephone. It is necessary that there is an outlet near the base unit, as the power adapter cable is usually short.

Starting to review the encountered defects in radiotelephones, let's say right away: up to half of the failures occur due to the fault of the owners of the devices. For example, picking up a handset with wet hands or using it in a bathroom will eventually lead to oxidation of the handset board conductors, leaks in the narrow gaps between them, and failure to function. Usually, in this case, it is enough to wash the tube board from the side of the conductors with a brush. Don't forget to disconnect the battery before doing this. What to wash? For example, I use solvent. It is impossible to wash the board well with alcohol and gasoline. Sometimes flushing doesn't help. Then it is necessary to restore the oxidized conductors.

Quite often there is a defect associated with the fall of the tube. As a result, microcracks can form, the search for which is a very difficult task. In handsets of radiotelephones, printed circuit boards of double-sided mounting are used to reduce the size. The conductors on them are connected by metallization of holes. These connections are also often torn. It is extremely difficult to detect such a defect. A little trick - when the metallization is destroyed, it changes color, becoming darker...

Let's move on to the battery. If it is discharged to a voltage below 3 V, the handset does not turn on. Advice to owners: if you are going away for a long time, it is best (for fire safety purposes) to turn off the phone from the mains. But at the same time, never forget to turn off the battery in the handset itself, otherwise it will be discharged, and this will negatively affect its service life.

Let's say you still forgot to disconnect the battery. It will most likely not be possible to charge it again by placing the handset on the base unit. Why? Yes, because the charging current is too small to wake up the "sleeping" batteries. However, you do not need to run to the store for new ones when it is possible to restore the old ones. Disconnect the power plug from the phone base unit. Take two wires and connect the power supply connector and the battery with them, observing the polarity. Hold for 20 ... 30 s, and then boldly insert everything into place. Just remember to put the handset on the base for at least four hours to charge the battery.

Briefly about the buttons. When using telephones (especially those manufactured by Panasonic), such a malfunction often occurs: the buttons do not work, it becomes more and more difficult to dial telephone numbers. There can be two reasons. The first of these is associated with contamination of contacts (for example, with grease), especially if the phone is in the kitchen. The second is the destruction of the graphite contact (piglet).

In the first case, the defect can be eliminated by wiping the patches and the board with cotton soaked in alcohol. And in the second, you will have to cut small circles or squares from aluminum foil and glue them to the patches. It is best to use the Polish adhesive SILIKON, used for sealing cracks in aquariums. This glue remains elastic after drying. By the way, this method is widely used in the repair of remote controls and calculators.

The technical illiteracy of the owners, their inattention and partly the difference in the standards that are followed at the enterprises of foreign firms also lead to defects in the devices. I'll give you an example. The power connector may have a different pinout. For Panasonic phones, the positive terminal is located on the outer contact of the connector, but for Toshiba or Sony phones, it is on the inner one. Although the connection polarity is indicated next to the socket, the owner, without looking at it, very often confuses the power supplies, spoiling the phone himself. And in response - silence and the smell of burning. What's happened? Yes, the stabilizer burned out. Usually it doesn't go beyond that. Of course, if you don’t be pushy and don’t try to connect the unit again ...

Author: M. Ryazanov, Moscow

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