Leader LTC-905 User manual

LEADER
CURVE TRACER
INSTRUCTION MANUAL

TABLE OF CONTENTS
Page
1. DESCRIPTION . 1
2. SPECIFICATIONS . 1
3. CONTROLS AND CONNECTORS . 1
4. OPERATION
4.1 Preliminary Notes . 3
4.2 Preparation . 5
4.3 Transistor Measurements .. 5
4.3.1 NPN, low level . 5
4.3.2 NPN, power type . 6
4.3.3 PNP, low level . 6
4.3.4 PNP, power type . 6
4.3.5 Measurement of hpg .. 7
4.4 Measurement of FET’s.. .. 8
4.4.1 N-cEannel FET, and N-channel MOS FET.. 8
4.4.2 P-channel FET, and P-channel MOS FET . 8
4.4.3 Mutual conductance, gm, measurement .. 8
4.4.4 Enhancement type FET measurement . 9
4.5 Diode Measurements
4.5.1 Standard test condition . 9
4.5.2 General purpose: Power rectifiers, detectors .10
4.5.3 Zener diodes .....10
4.5.4 Tunnel diodes ...10
4.5.5 Quantitative diode measurements ...10
4.6 SCR (Thyristor) Measurements.H
4.7 UJT (Unijunction transistor) Measurements. j j
5. Measurements with External Bias
5.1 General... 12
5.2 Transistor Measurements .... 12
5.2.1 Bias supplies . 12
5.2.2 hpg measurements.
5.2.3 IcEO measurements . jg

5.3 F ET Measurements.. . . . .. 2 3
5.3.1 Bias supplies .13
5.3.2 gm' measurements . 1 4
5.3.3 Pinch-off Voltage, Vp, measurement .-.14
5.3.4 Drain current, measurement.15
6. In-Circuit Testing...j 5
6.1 General..
6.1.1 Application .15
6.1.2 Use of In-Circuit Probe, LP-11 .15
6.2 Display of Defective Transistors, FET .16
6.3 Notes on In-Circuit Testing .17
7. MAINTENANCE.18
7.1 Removing the Panel from Case.18
7.2 Fuse Renewal.18
7.3 AC Input Connections.18

1.
DESCRIPTION
Curve tracing on a scope is made easy with the LTC-905. Characteristic curves of all types of
semiconductors can be accurately displayed. This is far superior to the conventional ohmmeter
checks for quality. In-circuit testing is possible for quick checks.
Two inputs are provided which enable comparison of two similar units.
LTC-905 is designed to test the following:
1. Transistors - NPN, PNP, FET and MOS FET.
2. SCR’s (Thyristors) and Triacs.
3. Diodes - rectifier, detector, zener and tunnel.
2. SPECIFICATIONS
Collector/Drain Sweep
Frequency
Voltage
Sweep Waveform
Current
Current Limiter
Step Generator
No. of Steps
Current per Step
Volt per Step
External Bias
Power Requirements
Size and Weight
Accessories
120Hz, or 100Hz (2 x line frequency).
8 steps: 10, 20, 30, 40, 50, 60, 80 and 100V; accuracy, ±10%.
(Rated voltage)
Fullwave rectified.
100mA, maximum.
100012 for low level transistors;
100S2 for power transistors.
7.
10, 20, 50/iA; 0.1, 0.2, 0.5, 1, 2mA; accuracy, ±5%.
0.1, 0.2, 0.5V; accuracy, ±5%.
One curve display.
100, 120, 200, 220, or 240V, 50/60Hz,
25VA maximum operating, and 6VA at standby.
240(W)X 90(H)X 170(D) mm, 2kg, (9^”X 3>f X 6K”; 4.5 lbs.)
Instruction manual . 1
3-lead cable (banana plugs/clips) . 2
Scope leads, 2 red and 1 black .1 set
In-circuit test probe, LP-11 . 1
3. CONTROLS AND CONNECTORS
®
POWER switch
Turns on the AC power.
(D
Pilot lamp
Indicates when AC power is on.
(D
POLARITY switch
Selects the mode of operation.
©
VERTICAL jacks Connections to vertical scope input.
©
EXT. BIAS jack
Connection to an external source to apply base or gate bias
for a one curve display.
i

© BASE CURRENT/
GATE VOLTAGE
switch
(7) Banana plug jacks
® TO-5 socket
© SELECTOR, lower
© SELECTOR, upper
© TO-5 socket
@ Banana plug jacks
@ COLLECTOR/DRAIN
SWEEP VOLTAGE
switch
@ CURRENT LIMIT
switch
© H. LENGTH control
@ HORIZONTAL jacks
Sets the bias current in eight steps and gate voltage in three
steps; provided with position for external bias.
One group for test lead connections:
Color ; Transistor
FET
Blue C - Collector D- Drain
Green
B - Base
G - Gate
Yellow
! E - Emitter
S - Source
For insertion of transistor under test.
Selects input at “A” or “B” side. At OFF, both sides are
disconnected.
Setting depends on type of transistor, NPN or PNP at
TRANS; MOS FET and FET at FET.
Same as ® .
Same as (7) .
With eight positions for setting the sweep voltage.
Set at SIGNAL for low level types and at POWER for power
types.
Adjusts the amplitude of the horizontal sweep on the scope.
Connections to horizontal scope input.
o

4. OPERATION
4.1 Preliminary Notes
A. A C Line Voltage.
The AC voltage for operation should be kept within ±10% of the rated value, see
CHART 1. When low, the performance will be affected; when high, damage may result
to circuit, components in the instrument.
CHART 1
Rating, V Range, V
Fuse
100
90 - 110
120
108 - 132
200
180 - 220
0.5A
220
198 - 242
240
216 - 264
The line fuse is 0.5A for all voltages.
Refer to Sect. 7.3 for primary connections when different voltages are used.
B. A C Input Phasing.
Unless the phase of the AC voltage to the LTC-905 and scope
are in proper relation, “double curves” will be displayed, see
Fig. 4-1. This can be corrected by reversing the AC plug connection
on the scope or LTC-905.
NOTE: When the scope is not provided with the DC input
to the horizontal amplifier, the proper display may not
be obtained.
Fig. 4-1 Double curve effect,
AC phasing not proper.
C. Collector or Drain Sweep Application.
In order to protect the transistors and diodes against damage, care must be taken in
application of the sweep voltage.
Voltages over 10V should not be used unless specially noted.
D. Scope Characteristics
The scope for curve tracing is used as an X-Y scope. It is necessary that the scope
satisfies the conditions in CHART 2.
3

CHART 2
i
Amplifier
Bandwidth '
i
Sensitivity,
minimum
Vertical
DC - 1kHz or higher
0.1V/cm, or /div.
Horizontal
DC, or AC - 1kHz or higher
lV/cm, or /div.
In quantitative measurements, particularly for hpp and g m , a scope with the vertical
gain calibrated in V/cm should be used. For ease in readouts, the V/cm sensitivities
converted to the most used mA/cm calibration at two settings of the CURRENT LIMIT
switch are listed in CHART 3.
CHART 3
Vertical
Sensitivity
CURRENT LIMIT Setting
SIGNAL
POWER
i
50mV/cm
0.5mA/cm
5mA/cm
0.1 V/cm
1 mA/cm
10m A/cm
0.2V/cm
! 2mA/cm
i 20mA/cm
0.5V/cm
! 5mA/cm
! 50mA/cm
By adjusting the H. LENGTH control for the trace to cover 10cm, the V/cm unit
horizontally can be correlated with the sweep voltage setting.
E.
Scope Connections and Settings.
Connections between the scope and LTC-905 are made with the three leads as
indicated in Fig. 4-2, red leads to vertical and horizontal inputs and black lead to
common ground.
Set the vertical gain initially at lOOmV/cm and the AC-DC
switch at DC.
Set the horizontal gain at maximum and the AC-DC
switch at DC (use AC coupling if DC is not provided).
4

4.2 Preparation
Switch settings:
POWER
CURRENT LIMIT
COLLECTOR/DRAIN
SWEEP VOLTAGE
BASE . GATE
CURRENT'VOLTAGE
SELECTOR: upper
lower
OFF.
SIGNAL.
10 V.
EXT BIAS
Type under test, TRANSistor or FET.
OFF.
Connections:
With proper attention to the terminals, the transistor is connected to the socket or
leads from the three jacks at “A” or “B” side. When comparing two units, use the
sockets and lead connections at both sides.
4.3 Transistor Measurements
4.3.1 NPN, low level.
Switch settings:
BASE CURRENT
COLLECTOR SWEEP
POLARITY
CURRENT LIMIT
SELECTOR: upper
lower
10 (lA.
10V.
NPN.
SIGNAL.
TRANS.
A or B, as connected.
The scope controls are adjusted for suitable display and proper positioning, see Fig. 4-3
and Fig. 4-4. Seven curves will be observed with Si transistors and eight curves with Ge
transistors. This serves as a check.
When the BASE CURRENT is set at 20juA, the height will be doubled.
The transistor can be said to be satisfactory when the curves are displayed as shown in the
figures.
5

4.3.2 NPN, power type.
For NPN power transistors, under the same conditions as in Sect. 4.3.1, set the CURRENT
LIMIT at POWER and BASE CURRENT at 0.1 up to 1mA.
As the COLLECTOR SWEEP VOLTAGE is gradually raised from 10V upward.
Do not increase the sweep voltage beyond the point where
the curves start to bend, the curves will be as shown in Fig. 4-5.
The region of the breakdown voltage can be read off.
For example, with the sweep voltage at 50V, adjust the H.
LENGTH control for the sweep to cover 10cm horizontally,
Fig. 4-5 Power transistor ° r 5V/cm ’ in this case - The collector-emitter voltage, V CE ,
„> can be read easily,
curves. The curves 1
start to bend.
By adjusting the H. LENGTH control for the trace to cover 10cm (or div.), the V/cm unit
can be correlated with the voltage settings.
NOTES. 1. When the sweep voltage and/or base current are increased, the transistor
will become heated.
2. Power transistors should be tested within as short a time as possible. This
will prevent overheating when the sweep voltage is over 10V and/or
when a large base current is flowing.
4.3.3 PNP, low level.
Switch settings:
BASE CURRENT
COLLECTOR SWEEP
POLARITY
CURRENT LIMIT
SELECTOR: upper
lower
10/uA.
10V.
PNP.
SIGNAL.
TRANS.
A or B, as connected.
The curve tracing procedure is the same as given in Sect. 4.3.1.
The curve display will be as shown in Fig. 4-6.
Fig. 4-6 PNP transistor
curves.
4.3.4 P NP, power type.
Set the switches as in Sect. 4.3.2 above with the following exception:
POLARITY at PNP.
The curve tracing procedure is the same as described for NPN power transistors. The same
care must be exercised to prevent overheating with high sweep voltages and base currents.
6

4.3.5 Measurement of hpg.
Measurement of h FE for an NPN transistor will be given; for the PNP type, the only
changes will be in the setting of the POLARITY switch at PNP instead of NPN Ind in the
direction of the curves.
The DC current amplification of a transistor is given by the relation -
Collector current, Ip
h FE = ---
Base current, Ig
For this measurement, a calibrated scope is required.
Referring to CHART 3 (Sect. 4.1, Parag. D) under SIGNAL of CURRENT LIMIT, the
vertical gain is set at O.lV/cm. Under this condition, the collector current is read off at ImA/cm.
With the Si transistor, seven typical curves for Ig in lOfiA steps from 0 to 60/iA are shown
in Fig. 4-7. On the 60/tA curve, I c = 4.2mA. By calculation,
h FE = 4.2 x 10' 3 / 60 x 10* 6 = 70.
In Fig. 4-8, curves for a typical Ge transistor are shown. From the I fi = 70/1 A, I c = 2.1mA
and hpg = 30.
Fig. 4-8 hp E measurement,
Ge transistor.
In the two examples given above, hpg measurements are collector-emitter voltage, V^g =
10V. Other measurements can be made when required with the sweep voltage at 20, 30V,
etc.
For hpg of power transistors, set the CURRENT LIMIT switch at POWER and the
POLARITY switch at NPN or PNP as required.
The scope sensitivity is set by reference to the POWER column of CURRENT LIMIT in
CHART 3.
For example, with the sensitivity at 0.2V/cm, the calibration will be 20mA/cm. By setting
the BASE CURRENT at 0.2mA, and SWEEP VOLTAGE at 50V (10cm length), curves in
Fig. 4-9 will be displayed. From the figure, Ig = 1.2mA and I c = 50mA.
Thus, hpg is approximately 41.7. Measurements of hpg
in this manner will be accurate within +10%.
For higher accuracy, use an external bias supply; details are
given in Sect. 5.
Fig, 4-9 hpg measurement,
power transistor.
7

4.4 Measurement of FET’s
4.4.1 N -channel FET, and N-channel MOS FET.
Switch settings:
GATE VOLTAGE
DRAIN SWEEP
POLARITY
CURRENT LIMIT
SELECTOR: upper
lower
0.1V.
10 V.
N-CHAN.
SIGNAL.
FET.
A or B, as connected.
Eight curves will be displayed as shown in Fig. 4-10. As the sweep voltage is increased, the
upper operating limits will be approached, see Fig. 4-11.
4.4.2 P -channel FET, and P-channel MOS FET.
Set the POLARITY switch at P-CHAN. Other switch settings are the same as in Sect. 4.4.1
above. Fig. 4-12 shows the curve display.
Fig. 4.-12 Curves for P-channel FET
and P-channel MOS FET.
4.4.3 M utual conductance, gm, measurement.
The gm measurement for the N-channel FET will be described; for the P-channel FET, the
only changes will be in the setting of the POLARITY switch at P-CHAN instead of N-CHAN,
and the curve direction.
8

In the FET, mutual conductance defined by the relation -
_ AI D
g m _ — a t constant Vjyc.
AV GS
The switch settings are the same as given in Sect. 4.4.1.
The CURRENT LIMIT switch is set at SIGNAL; the scope is set at O.lV/cm sensitivity.
Under this condition, the drain current will be calibrated at ImA/cm. The GATE VOLTAGE
is set at 0.1V and trace length at 10cm.
In Fig. 4-13, eight curves are shown between V GS = 0 to 0.7V. On the graticule, the drain
current between these two voltages are read off. From the figure, the change in Iq is 2.1mA,
and
gm
2.1 x 10~ 3
0.7
- 3 x 10 3 , or- 3 millimhos.
Fig. 4-13 gm measurement in FET.
4.4.4 Enhancement type FET measurement.
There are two types of the MOS FET, depletion and enhancement. Measurements hitherto
described relate to the N-channel FET of the depletion type wherein the drain current, Ip,
decreases when the gate-source voltage, V G g, is increased. In the enhancement type, there is
practically no drain current when V G g is zero but will increase when VG g is applied in the
positive direction.
Consequently, when testing the enhancement type, the upper SELECTOR switch must be
set at TRANS. This will provide bias with the correct polarity. Other switch settings are the
same as given in Sect. 4.4.1.
4.5 Diode Measurements
4.5.1 Standard test condition.
Switch settings:
COLLECTOR/DRAIN SWEEP
POLARITY
CURRENT LIMIT
SELECTOR: upper
lower
10V.
DIODE FORWARD.
SIGNAL.
Any setting.
A or B, as connected.
9

/
GATE
VOLTAGE
Any setting.
BASE
CURRENT
Connections:
The diode under test is connected to the tracer as follows: anode to collector jack
and cathode to emitter jack, as shown on the panel marking at the A or B side.
4.5.2 G eneral purpose: Power rectifiers and detectors.
Curves are shown in Fig. 4-14 for two characteristics, depending on the POLARITY switch
settings, namely, DIODE FORWARD and DIODE BACKWARD. For the diode in good
condition, the forward characteristic will be as shown.
Fig. 4-14 Diode characteristics.
4.5.3 Z ener diodes.
Under the standard test condition, set the POLARITY switch at DIODE BACKWARD.
The curve displayed will be as shown in Fig. 4-15.
Depending on the
characteristic, the sweep voltage can be increased to 20V or higher as
required. By setting the POLARITY switch at DIODE FORWARD,
the trace indicated with the dashed line will be displayed.
Fig. 4-15 Zener diode characteristics.
4.5.4 T unnel diodes
Under the standard test condition, Sect. 4.5.1 above, the curve will be displayed as shown
in Fig. 4-16.
Fig. 4-16 Tunnel diode
characteristics.
The curve at the right of the 0V axis with the polarity switch
at DIODE FORWARD. There will be a blank in the curve
(dashed part.) which is the negative resistance characteristic.
The curve at the left of 0V axis will be displayed when the
switch is set at DIODE BACKWARD.
4.5.5 Q uantitative diode measurements
By calibrating the horizontal axis in V/cm, the current/voltage characteristic can be
determined.
Set the trace length horizontally at 10cm. This will calibrate the sweep voltage at 1/10
(one-tenth) of the switch setting. For example, if set at 10V, then 1cm is equivalent to IV.
With use of the calibrated vertical scale, the forward “rise” in diodes, zener breakdown
voltage, etc., can be determined readily.
10

11

Curves for the UJT are shown Fig. 4-20. Since the curves will
be close together, set the H. LENGTH control to full clockwise
for spreading.
Fig. 4-20 UJT characteristics.
5. MEASUREMENTS WITH EXTERNAL BIAS
5.1 General
A single curve will be displayed when an external bias is applied to the transistor under test.
Accurate measurements of hpg and g m are possible.
The bias current or voltage source is connected to the EXT BIAS jacks. The BASE
CURRENT/GATE VOLTAGE switch is set at EXT BIAS.
5.2 Transistor Measurements
5.2.1 Bias supplies.
Circuits for supplying the external bias to the NPN and PNP transistors are shown in
Fig. 5-1 and Fig. 5-2.
The source, battery or regulated, should be in the 1 to 5V range; in most measurements,
a 1.5V cell is sufficient.
The variable resistor VR, about 50kf2, is used to adjust the current. A DC microammeter,
100 to 500/rA, will be suitable in most measurements. For power transistors, the range should
be 1 to 5mA.
5.2.2 hpp measurements.
Switch settings:
BASE CURRENT
SWEEP VOLTAGE
CURRENT LIMIT
SELECTOR: upper
lower
POLARITY
EXT. BIAS.
10V.
SIGNAL.
TRANS.
A or B, as connected.
NPN or PNP, depending on the transistor.
The scope sensitivity is set at O.lV/cm for calibration at ImA/cm.
Adjust the bias current with VR.
12

The curve for an NPN transistor will be as shown in Fig. 5-3.
For example, if the bias current, Ig, is set at 50/lA and collector
current, Iq, is 4mA (see curve), then
AI C 4mA 4 x 10' 3
"FE ~ ' , T = - = - = 80.
ai B 50 /uA 50 x 10" 6
The hpg can be measured at different values of Ig with
adjustment of VR.
For power transistors, set the CURRENT LIMIT switch at
POWER and follow the same procedure.
For PNP transistors, set the POLARITY switch at PNP; the
curve will inverted.
Disconnect the EXT BIAS connection, the I^go is
measured.
(External bias is not used.)
Fig. 5-4 shows the curve for a Ge type transistor where
the lego * s relatively high.
Fig. 5-4 IcEO measurement,
Ge transistor.
5.3 FET Measurements
5.3.1 Bias Supplies.
The bias voltage, Vq^, supplies for N-channel and P-channel FET’s are shown in Fig. 5-5
and Fig. 5-6. The output is connected to the EXT BIAS jacks as indicated. The source, battery
or regulated, should be in the 3 to 6V range. A lk£2 potentiometer, VR, and a suitable
voltmeter are required.
13

5.3.2 gm measurements.
Switch settings:
POLARITY N-CHAN or P-CHAN, depending on FET.
GATE VOLTAGE EXT BIAS.
SWEEP VOLTAGE 10V.
CURRENT LIMIT SIGNAL.
SELECTOR: upper FET
lower A or B, as connected.
The scope sensitivity is set at O.lV/cm for calibration at ImA/cm to read I D and for
V DS at IV/cm with the H. LENGTH control.
Procedure:
1. Note the Id( 0 ) reading at OV bias on the Vq§ = OV curve; the reading is taken where the
curve flattens out, see Fig. 5-7.
2. Next, set the bias at —0.5V and read Id(— 0.5V) on t ^ ie ^GS = — 1 0.5V curve.
3. The gm is defined as follows:
ai d
8m = AV GS
where Al D = I D ^ 0 j - I D (-0.5V), and
AV gs = OV - (—0.5V) = 0.5V
Then
gm
^(0) - lD(-0.5V) mA
05V
in millimhos.
In the above explanation, steps were given for gm measurement
at ^GS = an d —0.5V. Other measurements can be made
with different values of Vqj.
For the P-channel transistors, the curves will be inverted.
Fig. 5-7
hpE measurement
N-channel FET.
5.3.3 Pinch-off voltage, Vp, measurement.
Fig. 5-8 princh- off voltage
measurement.
An example will be given for the N-channel FET.
The switches and scope controls are set as given in Sect. 5.3.2.
Using the bias source, Fig. 5-5, the voltage from 0V is increased
in the minus direction. Curves will appear in the direction
indicated by the arrow in Fig. 5-8.
As more negative voltage is applied, the curve becomes
straight. The bias voltage measured at this point is the Pinch-off
voltage, Vp.
14

5.3.4 Drain current, Ijygg, measurements.
An N-channel FET will be used in the following example.
Disconnect the EXT BIAS connection and short the jack to ground. (External bias is not
used.)
The switches and scope controls are set as given in Sect. 5.3.2.
The curve for I DSS is shown in Fig. 5-9. I DS § is read off
at the point indicated with the arrow in the figure.
In general, the current is measured with V DS at 10V and
so the sweep voltage is set at 20V.
For FET’s with high current, set the scope sensitivity at 0.2V/cm
for the 2mA/cm calibration.
Fig. 5-9 ^DSS measurement.
6. IN-CIRCUIT TESTING
6.1 General
6.1.1 Application.
A valuable feature of the LTC-905 lies in its ability to test and/or compare transistors which
are wired in TV receivers, radios and other electronic equipment.
Tests for quality are made by reference to the instructions given for transistors in the
relevant sections on operation,
PRECAUTIONS:
1. For in-circuit testing, always turn off the operating power, AC or battery, to the
equipment.
2. Confirm the type of transistor before testing by reference to the schematic or a
handbook.
3. To prevent possible damage to the transistor and other circuit components, do not use
more than 10V for the sweep voltage.
6.1.2 Use of In-Circuit Probe, LP-11
Instead of clips used in testing transistors and FET’s which are mounted on circuit boards,'
the LP-11 Probe will be found very handy. The banana plugs are inserted in the panel jacks
according to the color.
There are three sharp prods equipped with swivel joints on the probe head. It will be noted
that two prods, blue for collector (drain) and yellow for emitter (source) are slightly longer
than the green prod for base (gate).
In use, after checking the proper terminals on the circuit board, the two longer prods are
connected first and the shorter prod is “bridged” for the connection. Sharp prods are used
to pierce the insulation on the solder.
For safety, always put the cover over the prods after use.
15

6.2 Display of Defective Transistors, FET’s
The conditions and typical displays of defective transistors and FET’s will be given in this
section.
1. Base-collector shorted in transistors.
Two displays are shown for the NPN type with base currents at 10/t A and 0.2mA in
Fig. 6 1 and Fig. 6-2. For the PNP type, the curves will be reversed in each figure.
Fig. 6-1
Fig. 6-2
2. Drain-gate shorted in FET’s.
In Fig. 6-3 and Fig. 6-4, two conditions, with eight curves, are shown for the N-
channel FET with gates voltages are 0.1V and 0.5V.
3.
Fi S- 6-3 Fig. 6-4
Collector-emitter, or Drain-source, shorted, or total short.
Only a vertical line will be displayed, above (PNPj or below (NPN) the
see Fig. 6-5.
zero axis,
16

4.
Base-emitter, or Gate-source, Shorted or total open.
This condition is shown in Fig. 6-6 where there is no indication
of the base current, or gate voltage.
Fig. 6-6
6.3 Notes on In-Circuit Testing
The shape of the displayed curves will be affected by presence of associated circuit
components. However, it may be assumed that the transistor or FET is satisfactory when a
plurality of curves is displayed.
For example, typical curves for an NPN transistor in circuit are shown in Fig. 6-7. It will
be seen that when the base current is increased, there will be considerable distortion in
the curves.
Fig. 6-7 In-circuit curves for NPN transistor.
In testing transistors, when only one curve is displayed, increase the base current from
10/tA to 20(1 A or 50(xA. Typical curves for different base currents are shown in Fig. 6-8.
Fig. 6-8 Effect of increasing the base current.
For FET’s, increase the gate voltage from 0.1V to 0.2V. When it is difficult to ascertain
whether the unit defective, it should be tested after removal from the circuit board.
17