Elenco Electronics DT-100 User manual

TRANSISTOR/DIODE TESTER
MODEL DT-100
Lesson Manual
ELENCO®
Copyright © 2012, 1988 REV-G 753115
Elenco®Electronics, Inc. Revised 2012

-1-
FEATURES
Diode Mode:
1. Checks all types of diodes - germanium, silicon, power, light
emitting (LEDs), and zener.
2. Indicates the cathode or anode leads of the diode.
3. Operates in circuit with resistors as low as 5kΩ.
Transistor Mode:
1. Checks all types of transistors - germanium, silicon, power, RF,
audio, switching, and FETs.
2. Identifies NPN and PNP types, PN or NP junctions.
3. High gain circuit, can test transistors in circuits with base or
collector resistors as low as 100Ω.
4. Measures relative beta of two transistors.

-2-
OPERATING INSTRUCTIONS
The DT-100 is a dynamic transistor and diode tester. It features in-
circuit testing and polarity indicators for both transistors and diodes.
To activate the DT-100, remove the four mounting screws from the
bottom and install a fresh 9V battery.
Diode Testing
1. Place the switch in the diode position.
2. Connect the diode to the red and black leads.
3.
Push in the test switch. One diode LED should blink and identify
whether the cathode or anode is connected to the diode (red) lead.
4. If both LED lamps blink, then the diode is shorted.
5. If neither LED lamps light, then the diode is open.
Transistor Mode:
The DT-100 can measure transistors in or out of circuit. It will identify
NPN or PNP by a simple adjustment.
Transistor Testing - Out of Circuit
1. Place the switch in the transistor position.
2. Place the transistor in the socket or attach it to the C, B, and E
leads.
3. Push in the test button. Adjust the base current control so that
the OK LED lights up. This indicates a good transistor.
4. If the OK lamp doesn’t light, adjust the base current control so
that either the NPN or PNP LED lights up. This happens at the
minimum or maximum position of the control setting. This will
indicate transistor type. Place the switch to the NPN position if
the NPN lamp lights up, or place the switch to the PNP position
if the PNP lamp is lit.
5. If no lamps light up, then the transistor is open or we have not
identified the base lead. Repeat assuming another lead at the
base.

-3-
6. When the transistor is shown to be OK, the base current control
gives an indication of transistor beta. The lower the setting
relative to another transistor, the higher the beta. Lamps NPN
and PNP measure base current. Higher base current results in a
brighter LED. It also indicates if current is entering or leaving the
base, thus, NPN or PNP respectively will light.
Transistor Testing - In Circuit
The DT-100 will test transistors in circuit, provided the base biasing
resistance is greater than 100Ω. Simply follow the previous
procedure for testing out of circuit transistors. Do not apply power
to the circuit of the transistor or diode under test. The DT-100 will
supply the necessary power.
CHECKING OUT YOUR TRANSISTOR/DIODE TESTER
The following is a simple procedure for testing your DT-100.
Diode Operation:
1. Place the switch in the diode position. Short the black and red
leads together and push in the test button. The diode test LEDs
should alternately go on at about a 1Hz rate.
2.
Connect the red and black leads to any good diode. Only one LED
should flash, identifying the red lead connection (anode or cathode).
Reversing the leads should cause the other LED to flash.
Transistor Operation:
1. Place the switch in the transistor position. Short the yellow (B)
and black (E) leads together. Press the test button.Vary the base
current control. The NPN lamp should light with the switch in the
NPN position and the PNP lamp when the switch is in the PNP
position.
2. Place a known good transistor in the test socket with the Emitter
in E, Base in B and Collector in C pins. Be sure none of the leads
are shorting. Vary the base current control. The OK LED should
light up. Note that on the NPN transistor, the NPN lamp also will
glow very slightly. This indicates the base current, and thus lower
intensity. The base current control should be adjusted for the
lowest setting with the OK lamp glowing.

-4-
THEORY OF OPERATION
Note the schematic diagram on page 6. The test transistor in this
circuit is an NPN. Adjusting the variable resistor will cause the NPN
LED to light up indicating that the base current is flowing.The output
of the test transistor is fed to amplifiers Q2 and Q3. The output of
Q2 is feedback in phase to the base of the test transistor causing
the circuit to oscillate. Part of the oscillations are fed to a power
rectifier, Q5, which switches on the OK LED indicator.
The design configuration is such that in-circuit transistors can be
measured, provided that the base and collector resistors are greater
than 100Ω.
When measuring PNP transistors, the power supplied to the test
transistor is reversed via the NPN/PNP switch. Therefore, the PNP
LED will light up.
Varying the base current control will reduce the base current. The
lower the base current, the higher the gain of the transistor under
test. Comparative tests of two transistors’ gain (beta), can be made
by observing the dial setting or the intensity of the base LED diode.
The lower the setting with the PNP LED lit, the higher the beta of
that transistor.
On diode operation, power is applied to IC1. This causes the circuit
to oscillate at about a 1Hz rate. Placing a diode in series with the
LED indicators will cause a current to flow, depending on the
direction of the diode.Thus, the red test lead will identify the cathode
or anode of the diode via the LED readout. Transistor Q4 reverses
the current flow in this circuit.
All types of diodes may be tested: Silicon, germanium, LEDs or
zeners over 6 volts. Zener diodes under 6V causes the second LED
to glow at lower intensity, indicating that zener breakdown has
occurred.

-5-
DT-100 PARTS LIST
Resistors 5% 1/4W
Qty. Symbol Value Color Code Part #
r1 R14 100Ωbrown-black-brown-gold 131000
r2 R5, R6 220Ωred-red-brown-gold 132200
r2 R1, R10 330Ωorange-orange-brown-gold 133300
r1 R13 1kΩbrown-black-red-gold 141000
r1 R7 5.6kΩgreen-blue-red-gold 145600
r1 R12 10kΩbrown-black-orange-gold 151000
r1 R8 18kΩbrown-gray-orange-gold 151800
r2 R2, R3 33kΩorange-orange-orange-gold 153300
r1 R9 47kΩyellow-violet-orange-gold 154700
r1 R11 100kΩbrown-black-yellow-gold 161000
r1 R4 330kΩorange-orange-yellow-gold 163300
r1 R15 100kΩVariable Potentiometer 192611
Capacitors
Qty. Symbol Value Description Part #
r1 C6 0.001μF (102) Discap 231036
r3 C2, C3, C5 0.01μF (103) Discap 241031
r2 C1, C4 10μF Lytic 271045
Semiconductors
Qty. Symbol Value Description Part #
r1 D1 1N4001 Diode 314001
r1 Q5 MPS A70 Transistor 320070
r4 Q1 - Q4 2N3904 Transistor 323904
r1 IC1 555 Integrated Circuit 330555
r5 L1 - L5 Light Emitting Diode 350002
Miscellaneous
Qty. Description Part #
r1 PC board 511100
r1 Switch push button 540001
r2 Switch DPDT 541111
r1 Battery snap 590098
r1 Knob 622009
r1 Case top 623061
r1 Case bottom 623062
r5 Spacer LED 624111
r4 Screw M3 x 5mm 640300
r4 Screw 2.8 x 8mm 641102
r1 Nut pot 7mm 644101
r1 Flat washer 645101
r1 Lockwasher 5/16” int. 646101
Qty. Description Part #
r4 Rubber feet 662015
r1 Socket 8-Pin IC 664008
r1 Transistor socket 664500
r1 Clip black 680001
r1 Clip red 680002
r1 Clip green 680003
r1 Clip yellow 680004
r1 Label top 724100
r1 Wire black 20 ga. 813110
r1 Wire red 20 ga. 813210
r1 Wire yellow 20 ga. 813410
r1 Wire green 20 ga. 813510
r1 Wire blue solid 22 ga. 814620

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SCHEMATIC DIAGRAM

ELENCO®
150 Carpenter Avenue
Wheeling, IL 60090
[phone]
Website: www.elenco.com
e-mail: [e-mail]
TWO YEAR WARRANTY
All ELENCO®models are guaranteed for two full
years on all parts and service. For the first 3
months, your transistor/diode tester is covered at
absolutely no charge. For the remaining 21 months,
a nominal service charge is required to cover
shipping and handling.
When returning merchandise for repair, please
include proof of purchase, a brief letter of
explanation of problem, and sufficient packing
material. Before returning any merchandise
please call our service department at (847)
541-3800 to obtain a return authorization
number (RMA).