Wavetek 180 - Troubleshooting Chart; Troubleshooting Individual Components

6
SECTION
TROUBLESHGOTiNG
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 inistrument 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 CHART
Troubleshooting charts are given in figure 6-1. The charts do
not cover every possible trouble, but will be an aid In
systematically isolating faulty components.
6.3 TROUBLESHOOTING INDIVIDUAL COMPONENTS
6.3.1 Transistor
1. 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.
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).
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
1. 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., UA741C, LM318)
1. The "+" and " inputs of an operational amplifier
will have less than 15 mV voltage difference when
operating under normal conditions.
2. If the output voltage stays at maximum positive, its
"+" input voltage should be more positive than its
" input voltage, or vice versa; 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.