Troubleshooting Equipment; Troubleshooting Techniques - Tektronix 7B70 Time Base Instruction Manual

Maintenance-7B7O (SN B205000 and Up)
stripes, the color code also indicates the type of diode or
identifies the Tektronix Part Number using the resistor
color code system (e.g., a diode colorcoded blue- or pink-
brown-gray-green indicates Tektrorlix Part Number 152-
0185-00). The cathode and anode ends of metal-encased
diodes can be identified by the diode symbol marked on
the body.
Troubleshooting Equipment
The following equipment i s useful for troubleshooting
the 7B70:
1. Transistor Tester
Description: Tektronix Type 576 Transistor-Curve
Tracer or equivalent.
Purpose: To test the simiconductors used in this
instrument.
Description: 20,000 ohms/volt. 0-500 volts DC.
Accurate within 3%. Test probes must be well insulated.
Purpose: To measure voltages and resistances.
3. Test Oscilloscope
Description: DC to 200 MHz frequency response, 5
millivolts to 5 volts/division deflection factor. Use a 10X
probe.
Purpose: To check waveforms in the instrument.
4. Plug-In Extender
Description: Rigid plug-in extender, Tektronix Part
number 067-0589-00.
Purpose: Permits operation of the unit outside the
plug-in compartment for better accessibility during
troubleshooting.
Troubleshooting Techniques
This troubleshooting procedure is arranged in an order
which checks the simple trouble possibilities before pro-
ceeding with extensive troubleshooting. The first few
checks ensure proper connection, operation and calibration.
I f the trouble is not located by these checks, the remaining
steps aid in locating the defective component. When the
defective component i s located, i t should be replaced fol-
lowing the replacement procedures given under Corrective
Maintenance.
1. Check Control Settings. Incorrect control settings
can indicate a trouble that does not exist. If there is any
question about the correct function or operation of any
control, see the Operating Instructions section.
2. Check Associated Equipment. Before proceeding
with troubleshooting of the 7B70, check that the equip-
ment used with this instrument i s operating correctly.
Check that the signal is properly connected and that the
probe cable is not defective. The indicator oscilloscope and
vertical plug-in unit can be checked for proper operation by
substituting another time-base unit which is known to be
operating properly (perferably another 7B70 or similar
unit). I f the trouble persists after substitution, the indicator
oscilloscope and/or vertical plug-in unit is defective.
3. Check Instrument Calibration. Check the calibration
of this instrument, or the affected circuit if the trouble
exists in one circuit. The apparent trouble may only be a
result of misadjustment and may be corrected by calibra-
tion. Complete calibration instructions are given in the Cali-
bration section.
4. Visual Check. Visually check the portion of the in-
strument in which the trouble is located. Many troubles can
be located by visual indications such a s unsoldered connec-
tions, broken wires, damaged components, etc.
5. Isolate Trouble to a Circuit. To isolate a trouble to a
circuit, note the trouble symptom. The symptom often
indicates the circuit in which the trouble is located. For
example, if normal triggering can be obtained in the INT
mode but carlnot be obtained in the EXT mode, the exter-
nal trigger amplifier or the SOURCE switch is probably at
fault. When trouble symptoms appear, use the front-panel
controls and the CRT display to try to isolate the trouble
to one circuit. When the trouble appears in more than one
circuit, check all affected circuits by taking voltage and
waveform readings.
Fig. 4-2 provides a guide to aid in locating a defective
circuit. This chart does not include checks for all possible
defects; use steps 6 and 7 for further troubleshooting. 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 is not
correct. Further checks and/or the circuit in which the
trouble is probably located are listed to the right of this
step.
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
components can be located by checking for the correct
Scans by ArtekMedia O 2006