Elenco Electronics XK-550, Instruction Manual

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TESTING THE XK-550 DIGITAL ANALOG TRAINER
The following paragraphs give detailed instructions
on testing the digital / analog trainer.
Note that in the XK-550 trainer there are five major
functions, (1) Power Supply (2) Logic Indicators (3)
Function Generator (4) Logic Switches and (5) Data
Switches.
We shall proceed in testing out each
section. If any test fails, refer to the schematic
diagram and check the wiring and soldering of the
section involved.
POWER SUPPLY TESTING
Plug the trainer into a 120VAC outlet and switch to
the “
ON ” position (the power switch should light).
With a digital voltmeter, measure the voltage
outputs at the power blocks.
The +12V should
measure between 11.4 and 12.6 volts. The 5V
supply should read between 4.75 and 5.25 volts.
The –12V supply should read between –11.4 and
12.6 volts.
Do not short the 15VAC output to ground.
Short the +12V, –12V and +5V supply to ground.
They should turn off and recover when the short is
removed. If you have a 25
Ω
10 watt resistor, place
it across the output terminal (2 watt resistor will
work, but use it only for a few seconds). The output
of the 12V supply should not change more than 0.20
volts. Do the same on the 5V supply using a 10
Ω
5
watt resistor. Again, the output should not change
more than 0.20 volts.
In making this test, the
voltmeter leads should be clipped to the terminal
directly and no to the load leads. This is to prevent
errors due to voltage drop from contact resistance of
the load.
Check the variable voltage supplies in the same
manner.
Set the output voltage between 10-15
volts. Place the 25
Ω
10 watt resistor across the
output terminal. The voltage should stay within 0.20
volts of the no load voltage.
TESTING THE FUNCTION GENERATOR
To test the function generator, you will need an
oscilloscope.
Connect the scope to the terminal
marked FREQ., and the ground clip to the terminal
marked GND. Adjust the waveform switch to sine,
the coarse frequency switch to 1k and the amplitude
control to maximum. Your scope should show a sine
wave with an output of about 15Vpp. If the sinewave
is clipped on top or bottom, adjust the DC offset
control for the most linear reading. Turn the FINE
ADJ control and the frequency should vary between
100 and 1000 hertz.
Check the other coarse
frequency positions.
Now, check the CLK output terminal. You should
see a square wave of about 5Vpp. If the scope is a
dual trace, connect one input to the CLK and the
other FREQ terminal. Set the waveform switch to
squarewave. You will note the two frequencies are
180
O out of phase. If no scope is available, connect
a wire to the CLK terminal and input to “A” of the
logic indicators. Connect another wire to the FREQ
terminal and input “B”. Set the coarse frequency
switch to 10 hertz and the fine freq control to
minimum position.
The two LEDs should blink
alternately.
TESTING THE LOGIC INDICATOR FUNCTION
There are eight logic indicators which you will be
checking out. Place a wire to the 5V power supply
and touch the “A” logic indicator test pin. The “A”
LED should light up. Remove the wire and the LED
should go out. Do the same for the B, C, D, E, F, G
and H test pins.