Tektronix 7A19 Instruction Manual page 14

Maintenance-7A19
4. Plug-in Extender--A fixture that permits operation of
the unit outside of the plug-in compartment for better
accessibility during troubleshooting. Order TEKTRONIX
Part No . 067-0616-00 .
Troubleshooting Procedure
This troubleshooting procedure is arranged in an order
which checks the simple trouble possibilities before pro-
ceeding with extensive troubleshooting .
1 . Check Control Settings . An incorrect setting of the
7A19 controls can indicate a trouble that does not exist. If
there is any question about the correct function or
operation of a control or front-panel connector, see
Section 2.
2 . Check Associated Equipment. Before proceeding
with troubleshooting of the 7A19 check that the equip-
ment used with this instrument is operating correctly . If
possible, substitute an amplifier unit known to be operating
correctly into the indicator unit and see if the problem
persists . Check that the input signals are properly con-
nected and that the
interconnecting cables are not
defective.
3. Visual Check . Visually check the portion of the
instrument in which the trouble is suspected. Many troubles
can be located by visual indications, such as unsoldered
connections, broken wires, damaged circuit boards, dam-
aged components, etc .
4 . Check Instrument Performance . Check the calibration
of the unit, or the affected circuit by performing Perfor-
mance Checks of Section 5. The apparent trouble may only
be a result of mis-adjustment and may be corrected by
calibration .
5 . Check Voltages . Often the defective component or
stage can be located by checking for the correct voltage in
the circuit. Typical voltages are given on the diagrams;
however, these are not absolute and may vary slightly
between instruments . To obtain operating conditions
similar to those used to take these readings, see the
instructions in the Diagrams section.
6 . Check Individual Components . The following
methods are provided for checking the individual com-
ponents in the 7A19 . Components which are soldered in
place are best checked by disconnecting one end to isolate
the measurement from the effects of surrounding circuitry.
4-2
A. TRANSISTORS AND INTEGRATED CIRCUITS .
The best check of transistor operation is actual perfor-
mance under operating conditions . If a semiconductor is
suspected of being defective, it can best be checked by
substituting a component known to be good ; however, be
sure that circuit conditions are not such that a replacement
might also be damaged . If substitute transistors are not
available, use a dynamic tester (such as TEKTRONIX Type
576) . Static-type testers may be used, but since they do not
check operation under simulated operating conditions,
some defects may go unnoticed . The schematic shows base
pin and socket arrangements of semiconductor devices. Be
sure the power is off before attempating to remove or
replace any semiconductor component.
Integrated circuits can be checked with a voltmeter, test
oscilloscope, or by direct substitution . A good under-
standing of the circuit description is essential to trouble-
shooting circuits using integrated circuits . Use care when
checking voltages and waveforms around the integrated
circuits so that adjacent leads are not shorted together .
B . DIODES . A diode can be checked for an open or for
a short circuit by measuring the resistance between termi-
nals with an ohmmeter set to the R X 1 k scale . The diode
resistance should be very high in one direction and very low
when the meter leads are reversed . Do not check tunnel
diodes or back diodes with an ohmmeter .
Do not use an ohmmeter scale that has a high internal
current. High currents may damage the diodes .
C. RESISTORS . Check resistors with an ohmmeter .
Resistor tolerance is given in the Electrical Parts List .
Resistors normally do not need to be replaced unless the
measured value varies widely from the specified value.
D . CAPACITORS . A leaky or shorted capacitor can be
detected by checking resistance with an ohmmeter on the
highest scale. Use an ohmmeter which will not exceed the
voltage rating of the capacitor. The resistance reading
should be high after initial charge of the capacitor. An open
capacitor can best be detected with a capacitance meter, or
by checking whether the capacitor passes AC signals.
7. Repair and Readout the Circuit. Special techniques
required to replace components in this unit are given under
Component Replacement. Be sure to check the perfor-
mance of any circuit that has been repaired or that has had
any electrical components replaced . Recalibration of the
affected circuit may be necessary .