Circuit Description - Elenco Electronics XK-150 Instruction Manual

TESTING THE LOGIC INDICATOR FUNCTION
There are eight logic indicators which you will be testing. Place a wire to the 5V terminal and touch the "0" LED
logic indicator terminal. The "0" LED should light up. Remove the wire and the LED should go out. Do the same
for the 1, 2, 3, 4, 5, 6 and 7 logic terminals.
TESTING THE LOGIC SWITCHES
There are two logic switches and four conditions to be tested. Connect a wire from the "A" terminal to the "7" LED
logic indicator terminal. Connect another from the "A" terminal to the "6" LED logic indicator terminal.
Note that the "7" LED logic indicator should be lit when the logic switch is in the "A" positions and the "6" LED
is not lit. Moving the logic switch to "A" should reverse the indicator LEDs, that is the "6" LED should light and
the "7" LED not light. Check the B logic switch in the same manner.
TESTING THE DATA SWITCHES
There are eight data switches to be tested. When the switch is in the up position, the output is at 5V. When the
switch is in the down position, the output is at ground. Place all the switches in the down position. Connect a
wire from the SW0 terminal and the "0" LED terminal. The "0" LED should light when the switch is placed toward
the top case. Repeat the same test on SW1, SW2, SW3, SW4, SW5, SW6 and SW7.
This completes the testing of the trainer.

CIRCUIT DESCRIPTION

The XK-150 Power Supply features two variable output voltages and a fixed 5V. The variable voltages are 1.25V
to 15V and --1.25 to --15V at up to .25 ampere maximum current. All supplies are regulated to better than .2V when
going from no load to full load. Varying the input AC voltage from 105 to 135V will have practically no effect on the
output voltages. This is because of the specially designed IC circuits used in the XK-150 circuits. Severe
overloading or even shorting the output circuits will not damage the supplies. Special turn-off circuits in the IC
sense the overload and turn off the output.
THE POSITIVE 1.25 TO 15V POWER SUPPLY
Figure 1 shows a simplified circuit diagram of the positive supply. It consists of a power transformer, a DC
rectifier stage and the regulator stage.
120VAC
Input
TRANSFORMER
The transformer T1 serves two purposes. First, it reduces the 120VAC input to 34VAC to allow the proper
voltage to enter the rectifier stages. Second, it isolates the power supply output from the 120VAC line. This
prevents the user from dangerous voltage shock should he or she be standing in a grounded area.
17VAC
Transformer
120V to 17V
Simplified diagram of positive power supply
20VDC
AC to DC
Converter
Figure 1
-6-
1.25 - 15V
Voltage
Regulator
Regulated
Output