Tektronix 7623, Instruction Manual

Page: 112 / 266

Maintenance —7623/R7623 Service
Check that the signal is properly connected and that the
interconnecting cables are not defective. Also, check the
power source. The associated plug-in units can be checked
for proper operation by substituting other units which are
known to be operating properly (preferably of the same
types). If the trouble persists after substitution, the 7623 is
probably at fault.
3. Visual Check.
Visually check the portion of the
instrument in which the trouble is located. Many troubles
can be located by visual indications such as unsoldered
connections, broken wires, damaged circuit boards,
damaged components, etc.
4. Check Instrument Calibration.
Check the calibration
of this instrument, or the affected circuit if the trouble
appears in one circuit. The apparent trouble may only be a
result of misadjustment, or may be corrected by calibra­
tion. Complete calibration instructions are given in the
Calibration section.
5. Isolate Trouble To a Circuit. To isolate trouble to a
particular circuit, note the trouble symptom. The symptom
often identifies the circuit in which the trouble is located.
For example, poor focus indicates that the CRT circuit
(includes high-voltage supplies) is probably at fault. When
trouble symptoms appear in more than one circuit, check
affected circuits by taking voltage and waveform readings.
Typical voltages and waveforms are given on the schematics
in the Diagrams section.
TABLE 4-2
Power Supply Tolerance and Ripple
Power
Supply Test Point
Output
Voltage
Tolerance
Maximum
ripple
(peak-to-peak)
-50 Volt TP -50 (back of
Main Interface
board) on
P1170-Pin 1
±0.1 volt 5 mV
-15 Volt P1170-Pin8 ±0.3 volt 2 mV
+5 Volt P1170-Pin 6 ±0.15 volt
2 mV
+ 15 Volt
P1170-Pin 5 ±0.3 volt 2 mV
+50 Volt
P1170-Pin4 ±0.6 volt 5 mV
+ 130 Volt P1170-Pin 3 ±5.2 volts 300 mV
If incorrect operation of the power supplies is suspected,
connect the 7623 to a variable autotransformer. Then,
check for correct regulation with a DC voltmeter (0.1%
accuracy) and correct ripple with a test oscilloscope while
varying the autotransformer throughout the regulating
range of this instrument.
After the defective circuit has been located, proceed
with steps 6 and 7 to locate the defective component(s).
6. Check Voltages and Waveforms. Often the defective
component can be located by checking for the correct
voltage
or waveform in the circuit. Typical voltages and
waveforms are given on the diagrams.
Incorrect operation of all circuits often indicates trouble
in the power supply. Check first for correct voltage of the
individual supplies. A defective component elsewhere in the
instrument can appear as a power-supply trouble and may
also affect the operation of other circuits. Table 4-2 lists
the tolerances of the power supplies in this instrument.
These voltages are measured between the power-supply test
points (see Section 2 for test-point location) and ground. If
a power-supply voltage is within the listed tolerance, the
supply can be assumed to be working correctly. If outside
the tolerance, the supply may be misadjusted or operating
incorrectly. Use the procedure given in the Calibration
section to adjust the power supplies.
Fig. 4-6 provides a guide for locating a defective circuit.
This chart does not include checks for all possible defects;
use steps 6 and 7 in such cases. Start from the top of the
chart and perform the given checks on the left side of the
page until a step is found which does not produce the
indicated results. Further checks and/or the circuit in which
the trouble is probably located are listed to the right of this
step.
NOTE
Voltages and waveforms given on the diagrams are
not absolute and may vary slightly between instru­
ments. To obtain operating conditions similar to
those used to take these readings, see the first
diagram page.
7. Check Individual Components.
The following
procedures describe methods of checking individual
components in the 7623. Components which are soldered
in place are best checked by first disconnecting one end.
This isolates the measurement from the effects of
surrounding circuitry.
A. SEMICONDUCTORS.
Power switch must be turned off before removing or
replacing semiconductors.
4-8