Elenco Deluxe Digital / Analog Trainer with Tools - Manual (Page 11)

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FUSE REPLACEMENT
1. Turn the trainer off and unplug it from 120VAC power source.
2. Unscrew fuse holder cap and remove fuse.
3. Use only a 1.25A fuse. Larger fuses or other fuse bypass will void the
warranty of the trainer.
4. Place the new fuse into the fuse holder cap and screw it back into the holder.
5. Plug trainer into 120VAC power source and turn the unit on.
The XR-2206 is comprised of four functional blocks,
a voltage controlled oscillator (VCO), an analog
multiplier & sine shaper, a unity gain buffer amplifier
and a set of current switches.
The VCO actually produces an output frequency
proportional to an input current. Across pins 5 and
6, a timing capacitor, is switched on to give 5
different ranges of frequencies via COARSE FREQ.
switch. On pin 7, the FINE FREQ. ADJ. variable
resistor controls the actual frequency output. These
two components form the RC time constants for the
oscillator frequency.
The VCO produces a squarewave signal. This
squarewave is sent to a shaper and converted into
a sine wave.
THE LOGIC INDICATORS
There are eight logic indicators. Figure 9 shows the
circuit. It consists of a 74HC04 IC. When the input
is over 2.8V, the output of the IC will be low, drawing
current through the LED indicator. The 120 ohm
resistor limits the current in the LED to about 30mA.
100k Ω
100k Ω 120 Ω
74HC04
LED
5V
Figure 9