Troubleshooting Individual Components; Operational Amplifier; Logic Levels; 6.4.2 Diode - Wavetek 75 Instruction Manual

10 DIM A$*60
20 SET @5:HVAL ("8E4F") !SET UP INTERFACE
30 WRITE @5:"!" !GO TO REMOTE
40 DO
50 WRITE @5:"XT3 I?"
60 READ @5:A$
70 LOOP
80 END
Figure 6-7. RS-2324 Sample Check Out Program
6.4 TROUBLESHOOTING INDIVIDUAL COMPONENTS
6.4.1 Transistor
1. A transistor is defective if more than 1 Vdc is
measured across its base emitter junction in the for-
ward direction.
2. A transistor, when used asa switch, may have afew
volts reverse bias voltage across the base emitter
junction.
3. If the collector and emitter voltages are the same,
but the base emitter voltage is less than 500 mV for-
ward voltage or reverse biased, the transistor is
defective.
4. In a transistor differential pair (common emitter
stages), either their base voltages are the same in
normal operating condition, or the one with less for-
ward voltage across its base emitter junction should
be off (no collector current); otherwise one of the
transistors is defective.
6.4.2 Diode
A diode (except a zener) is defective if there is greater
than 1 Vdc (typically 0.7 Vdc) forward voltage across it.
6.4.4 Field Effect Transistor (FET)
No measurable gate current should be drawn by the gate
of an FETtransistor. If so, the transistor isdefective. Gate
to source voltage is always reverse biased under a
normal operating condition; e.g., the source voltage is
more positive than the gate voltage for 2N5485 and the
source voltage is more negative than gate voltage for
a 2N5462. Otherwise, the FET is defective.
6.4.5 Capacitor
1. Shorted capacitors have OVacross their terminals.
2. Open capacitors can be located (but not always) by
using a good capacitor connected in parallel with
the capacitor under test and observing the resulting
effect.
3. Leaky capacitors will often have a decreased
voltage across their terminals.
6.4.6 Logic Levels
Table 6-30. Logic Levels by Family
(Except Where Otherwise Noted)
6.4.3 Operational Amplifier
1. Generally the
"
+
"
and
"
-
"
inputsof anoperational
amplifier will have less than 15 mvvoltagedifference
when operating under normal conditions.
2. When theoutput of theamplifier isconnected tothe
I '
-
l l input (voltage follower connection), the output
should be the same voltage as the
"
+ "
input
voltage; otherwise, the operational amplifier is
defective.
3. If theoutput voltage staysat maximum positive, the
"
+
"
input voltage should be more positive than
6 ' - , I input voltage, or vice versa; otherwise, the
*Inputs match 74LSxxx levels and outputs match
operational amplifier is defective. 74HCxxx levels.
6-20
Scans by ArtekMedia O 2006
Min Low
0.9V
0.9V
0.8V
0.8V
0.8V
1 .5v
0.8V
Logic Family
74HCxxx
74HCTxxx'
74ASxxx
74LSxxx
74Fxxx
4xxx
Microprocessor and
Memories
Min High
3.1 5V
3.1 5V
2.0V
2.0V
2.0V
3.5v
2.0V