Probe for testing radio equipment. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Probe for testing radio equipment. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Several years ago, a probe [1] and a device [2] were published in the Radio magazine, intended for use in testing, adjusting and repairing audio equipment. After repeating both designs, I was convinced that they work well, but they have relatively large dimensions, low sensitivity and consume a lot of current. In addition, these instruments do not test low-voltage (3 V) receivers or players without an external power supply.

I had to look for other solutions. As a result, it was possible to construct a relatively simple and small-sized probe (see Fig.), which uses the K174XA10 microcircuit and only a few parts.

Probe for testing radio equipment

The probe is powered by the device under test operating with a voltage source of 3...9 V. At 3 V it consumes 5 mA, at 5 V it consumes 10 mA, and at 9 V it consumes 15 mA. Its maximum sensitivity is such that you can listen to a signal taken directly from the outputs of the reproducing (universal) head of a tape recorder or player.

The advantage of the probe is that its manufacture does not require a printed circuit board. Details (any small-sized ones) are interconnected by hinged mounting and placed, say, in a case from under the Tick-tock dragee. Probe X1 - a piece of copper wire with a diameter of 2 ... 3 mm and a length of 30 ... 50 mm. One end of the probe is sharpened and tinned, and the other end is passed through a hole drilled in the housing and soldered to the positive terminal of capacitor C1. Two more holes are drilled next to the probe in the case, through which wires about 30 cm long are brought out: a crocodile clip (X2) is soldered to one (common), and the other is cleaned at the end - it will have to be soldered to the power source of the device. If its voltage exceeds 9 V, a stabilizer from resistor R2 and a zener diode VD1 (shown in dashed lines) should be connected to this conductor, and the conductor from the left one should be soldered to the device according to the resistor R2 output circuit. The variable resistor R1 (SP3-26b) is fixed so that part of its handle comes out through a hole cut in the side wall of the case (as in pocket receivers).

One of HD-11A stereophone capsules (made in China) or any other small-sized one was used as a head phone. The X3 connector for it can be mounted on the housing wall or brought out, but the connecting conductors in this version should be as short as possible.

They work with a probe like this. Clamp X2 is connected to the case of the device under test, and the conductor from the capacitor C3 is connected to the positive terminal of the power source. A headphone plug is inserted into the X3 connector, after which the X1 probe touches the terminals of the parts of the cascades under test. If, say, a player is being checked, a cassette is inserted, the playback mode is turned on, and the amplification path is checked from the universal head. Moving further along the cascades to the output, they determine the place where the signal ceases to be heard. This will indicate a fault in the cascade. The volume of the listening signal is regulated by a variable resistor R1.

Literature

Mini-probe for audio equipment. (According to the pages of foreign magazines). - Radio, 1996, No. 7, p. 56.
Storchak K. A device for repairing audio equipment. - Radio, 1994, No. 10, p. 24.

Author: E.Zuev, Denyatino, Vladimir Region

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