Elenco Digital / Analog Trainer Kit Version - Manual (Page 46)

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TESTING THE DIGITAL SECTION
TESTING THE LOGIC INDICATOR FUNCTION
There are eight logic indicators which you will be checking out. Put 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 pins.
TESTING THE LOGIC SWITCHES
There are two logic switches and four conditions to be checked out. Connect a wire from the “X” test pin to the
“A” logic indicator test pin. Connect another wire to the “X” test pin to the “B” test pin.
Apply power and note that the “A” LED indicator should be lit when the logic switch is in the “X” position and the
“B” LED should light and the “A” LED not light. Check the “Y” logic switch in the same manner.
TESTING THE DATA SWITCHES
There are eight data switches to be checked. The output of the switches are 5V or ground depending on the
position. Connect a wire to the SW1 test pin and the “A” test pin. The “A” LED should light when the switch is
placed toward the top of the case. Repeat the same test on SW2, SW3, SW4, SW5, SW6, SW7 and SW8.
Unplug the unit from the AC outlet.
DIGITAL TROUBLESHOOTING CHART
PROBLEM POSSIBLE CAUSE
No +5V on data switch terminals. 1. Measure for a DC voltage of +5V across R15.
A. Check R15, J19, J23 and J13.
B. Switch shorted to ground.
LED doesn’t light 1. Check that the LED is in correctly.
2. Check the input and output resistors.
3. Measure input for +5V and output at ground.
A. Short to ground or defective IC.
LED always on 1. Measure for zero voltage voltage at input pin.
A. Pin shorted or defective IC
2. Measure voltage to output pin for +5V.
A. Pin shorted or defective IC.
Logic switch terminal always high 1. Check that input resistor is grounded.
A. Bad ground connection or switch.
2. Measure for +5V on R16 - R19.
A. Check resistor.
3. Defective IC.