Tektronix 1L20, Инструкция по эксплуатации

Страница: 30 / 117

Maintenance— Type 1L20
Check Individual Components. The follow ing procedures
describe methods of checking individual components in the
Type 1L20.
Transistors. The best check o f transistor operation is actual
performance under operating conditions. To check tran­
sistors using a voltmeter, measure the emitter-to-base and
emitter-to-collector voltage and determine if the voltages
are consistent with the normal circuit voltages given on the
schematic diagrams.
TABLE 4 -5
PI 1 Connector (Mounted on Rear Plate)
Meter
Pin Resistance in Ohms1
(Reversed Polarity)
1 70 k a 84 k a
2 0
0
3 5.4 k a 5.4 k a
4 - 8
NC
9 5.4 k a 5.6 k a
10 4.6 k a
3.4 k a
11 50 k a 200 kO
1 2 - 1 4 NC
15
2.4 k a 2.3 k a
16
NC
NOTE
The shielded chassis of the Type 1L20 make it very
difficult to reach much of the socket wiring for
waveform and voltage checking. In many cases, it
is easier to take these measurements from the top
of the chassis by touching the probe to the tran­
sistor lead between the transistor body and the
socket pin. This is especially true of the black
epoxy-cased transistors. (See Fig. 4 -5 .)
If there is some doubt about whether a transistor is good,
substitute a new transistor; but first, be certain a defect in
the circuit did not cause the first transistor to fail. Other­
wise the new transistor may be damaged as soon as it is
subject to the same conditions. If the original transistor is
good, return it to the same socket. Unnecessary replace­
ment of transistors is not only expensive but may also result
in needless recalibration of the instrument.
If substitute transistors are not available, a dynamic tester
such as a Tektronix Type 575 may be used. Static-type
testers are not as meaningful since they do not check opera­
tion under operating conditions.
Diodes. A diode can be checked for an open or shorted
condition by measuring the resistance between terminals.
W ith an ohmmeter scale having an internal source of about
1.5 volts, the resistance should be very high in one direction
and very low when the leads are reversed.
CAUTION
Do not use an ohmmeter scale that has a high
internal current, and do not use this technique to
check tunnel diodes.
TABLE 4 -6
IF Chassis Square-Pin Connectors Meter.
Resistance in Ohms1
Pin
Cable Connected Cable Disconnected
A 0 0
B 1 k
00
C
00
oo
D 5.6 k a
90 k a
E 3 k a 4 k a
F 2 k a
Reverse Polarity
2.7 k a
Reverse Polarity
1.8 k a 3.5 k a
G n k a 2.5 k a 00 2.7 k a
H 3 k a
2.4 k a 00 4.2 k a
1
i i k a 2.8 k a
00 2.9 k a
J 850
850 280 k a 2.7 k a
K 27 k a
6 k a 220 k a 14 k a
L 90 k a
3.7 k a
00
4 k a
M 5 k a
250 k a i i k a
oo
N
lo o k a 2.7 k a
00 2.7 k a
O
lo o k a 2.7 k a 00 2.8 k a
P
lo o k a
6 k a 150 k a 00
Resistances printed in the tables were measured with a Simpson Electric Co. Model 262 Multimeter.
0 £2 — 40 kfi readings were taken on the R X 1 k range.
50 kfi—
CO
readings were taken on the R X 100 k range.
4 -8