Signal tracing by means of a signal tracer otfers a valuable method for servicing a variety of electronic equipment. This method is often employed when a
circuit is not completely dead, but rather malfunctioning. AM and FM receivers, CD players, multimedia amplifiers, TV sets, etc., can be serviced using
this simple signal tracer.
The circuit we show here consists of a two-stage direct-coupled transistor
amplifier. The circuit has two inputs. When the probe is used in the RF mode
the detector diode is inserted into the circuit. When the probe is used in the
audio mode the signal is applied directly to the base of the first transistor
(o1).
As the circuit has a low-power output, a gain control is not used.
The circuit is powered from two M cells, and current drain is only few milliamperes. Since the circuit draws such low current, long battery life can be
expected.
Figure I shows the schematic diagram of the signal tracer. R1 determines
the gain of the amplifier stage and can be altered to get better performance
depending on the transistors used.
Figure 2 shows the signal tracer mounted on a terminal strip, which is used
as a chassis.liake care with the transistors; one is an NPN and the other is a
PNP. lf you switch one with the other the circuit will not work.
This project can be housed in a small plastic box. The size of the plastic box
is determined by the speaker size. Position of the polarized pieces should be
observed.
Parts List - Signal Tracer
Ql - 8C548 general-purpose NPN silicon transistor
Q2 - 8C558 general-purpose PNP silicon transistor
D1 - 1N34 or equivalent - any germanium transistor
R1 - 1,500,000 ohm, 114W,5% resistor
C1 - 0.1 uF ceramic or metal film capacitor
C2 - 100 uF, 6 WVDC electrolytic capacitor
SPKR - 4/8 ohms - 2 or 4 in. smalloudspeaker
S1 - SPST slide or toggle switch
B1 - 3V - two AA cells
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