Elenco DataCom Tester Kit - Manual (Page 2)

GENERAL DISCUSSION
You can see a block diagram of the TCT-255 in Figure 1 below.
The TCT-255 Cable Tester has five basic blocks:
1. Power Supply
It powers all of the circuits of the tester (not including the terminator). The power supply has a low battery
indicator (less than 7.5V) and a circuit to disconnect power 30 - 50 seconds after the last push on the
test switch.
2. Oscillator
Uses a 555 timer IC with two resistors and one capacitor. They control the free running frequency and
duty cycle.
3. Step Pulses with Counter
The outputs change by the positive pulses from the test button switch.
4. Switches and LED Indicator
It includes eight electronic switches for operating the indicators (16 LEDs).
5. Terminator
Connected to cable under test. Identifies the polarity signals.
Cable Tester TCT-200 Terminator LD-100
Figure 1
COUNTER SWITCHES
INPUT & OUTPUT
CONNECTORS
INPUT & OUTPUT
CONNECTORS
STEP PULSES
OSCILLATOR
LED
INDICATOR
CIRCUIT
IDENTIFY
POLARITY
POWER
SUPPLY
-1-
The TCT-255 Cable Tester is a convenient
instrument for testing different unshielded wiring
schemed communication cable with RJ-11 and RJ-
45 connectors and coax cable. This tester can be
used for testing cables before and/or after they are
installed. The tester offers easy operation by having
to push only one button. Testing status is indicated by
multiple LEDs and an auto power-off function
maximizes battery life.
The unique design of the TCT-255 allows you to
place the parts over their corresponding symbol in
the schematic drawing on the surface of the PC
board during assembly. This technique maximizes
the learning process while keeping the chances of
an assembly error at a minimum. It is very
important, however, that good soldering practices
are used to prevent bad connections.
The actual assembly is broken into SEVEN
SECTIONS. After each assembly, you will be
instructed to make certain tests and measurements
to prove that each section is functioning properly.
The theory for each section, or stage, should be
read before the test is started. This will provide the
student with an understanding of what that stage
has been designed to accomplish, and how it
actually works. If a test fails to produce the proper
results, a troubleshooting guide is provided to help
you correct the problem. For testing you need to
have only a voltmeter for measuring DC and AC.
INTRODUCTION