Wavetek 143 - Page 31

6.1 FACTORY REPAIR
Wavetek maintains a factory repair department for those
customers not possessing the necessary personnel or test
equipment to maintain the instrument. If an instrument is
returned to the factory for calibration or repair, a detailed
description of the specific problem should be attached to
minimize turnaround time.
6.2 TROUBLESHOOTING CHARTS
Troubleshooting charts are given in figures 6-1 thru 6-9.
The charts do not cover every possible trouble, but will be
an aid in systematically isolating faulty components.
Figure 6-1. Initial Checks, Generator Board
Figure 6-2. Generator Loop Checks, Generator Board
Figure 6-3. VCG Checks, Generator Board
Figure 6-4. Generator Output Checks
Figure 6-5. Trigger and Gate Mode Checks, Trig/Pulse Board
Figure 6-6. Power Supply Checks, Trig/Pulse Board
Figure 6-7. Generator Input and Output Checks
6.3 TROUBLESHOOTING INDIVIDUAL COMPONENTS
6.3.1 Transistor
ΠΕ A transistor is defective if more than one volt is mea-
sured across its base emitter junction in the forward
direction.
2: A transistor when used as a switch may have a few
volts reverse bias voltage across base-emitter junction.
3. If the collector and emitter voltages are the same, but
the base emitter voltage is less than 500 mV forward
voltage (or reversed bias), the transistor is defective.
4. A transistor is defective if its base current is larger
than 10% of its emitter current (calculate currents from
voltage across the base and emitter series resistors).
SECTION
TROUBLESHOOTING
5. In a transistor differential pair (common emitter
stages), either their base voltages are the same in
normal operating condition, or the one with less
forward voltage across its base emitter junction
should be off (no collector current); otherwise, one
of the transistors is defective.
6.3.2 Diode
% A diode is defective if there is greater than one volt
(typically 0.7 volt) forward voltage across it.
6.3.3 Operational Amplifier (e.g., 741, 1458)
12 The “+” and “—” inputs of an operational amplifier
will have less than 15 mV voltage difference when
operating under normal conditions.
2: When the output of the amplifier is connected to the
“ input (voltage follower connection), the output
should be the same voltage as the “+” input voltage;
otherwise, the operational amplifier is defective.
6.3.4 Capacitor
1; Shorted capacitors have zero volts across their termi-
nals.
2: Opened capacitor can be located (but not always) by
using a good capacitor connected in parallel with the
capacitor under test and observing the resulting effect.
6.3.5 Digital TTL IC's (e.g. 7400 Series)
1. The device is operating correctly if the output high
state is > +2.4V and low state is < +0.5V.
2. The input must show the same two levels as in step 1.
If the levels are between +0.8V and +2.0V, the con-
nection to the driving circuit output is open.
6-1