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Troubleshooting
6–68
TDS 684A, TDS 744A, & TDS 784A Service Manual
Do all
the channels
display defective
waveforms?
Attach a probe to the PROBE COMPENSATION
signal located on the front of the oscilloscope.
Connect the probe to a channel’s BNC on the
front, select the channel and view the output on
the display. Do this for all the channels.
For all
the channels, is the
signal on the display a
1 kHz ±0.250 V
square wave?
Yes
No
No
Yes
The Acquisition/Attenuator Interface is ok.
Yes
No
Attach the PROBE COMPENSATION signal to
the CH 1 BNC on the front of the oscilloscope.
Remove the coax connector from J1400 on the
A10 Acquisition module.
Probe J700 but DO NOT
REMOVE the cable from the
connector. The voltages will
change if the A10 Acquisition
module is not connected to
the power supply.
Probe
J700 pins 10, 36,
16, and 8. Are these
pins +15 V, +5 V,
–5.1 V, and –15 V
respectively?
Perform the Low Voltage
Power Supply
troubleshooting
procedure.
Replace the A15
Attenuator module.
Replace the A10
Acquisition module.
Is a 1 kHz
±0.250 V square
wave displayed
now?
Set all the channels to the same vertical scale
and select a channel that works correctly. Attach
the PROBE COMPENSATION signal to a
defective channel’s BNC on the front of the
oscilloscope and swap these two channels’
coaxes to the A10 Acquisition module.
No
Yes
Replace the A15
Attenuator module.
While
turning the
vertical SCALE knob
again, does J1153 pin 26
swing between +5 V
and 0 V?
No
Yes
While
turning the vertical
SCALE knob, does J1153
pin 24 pulse low
swinging between
+5 V and
0 V?
No
Yes
Probe
the detached end
of the coax. Is there a 1 kHz
±0.250 V square wave on
the coax?
No
Yes
Power the oscilloscope off and disconnect the cable
attached to J1153 on the A10 Acquisition module.
Power on and probe J1153 pins 14, 16, 18, and 20.
Are these
pins +15 V, +5 V,
–5.1 V, and –15 V
respectively?
No
Yes
While
turning the
vertical SCALE
knob, does J1153 pin 22
pulse swing between
+5 V and 0 V.
Yes
No
Figure 6–35: Attenuator/Acquisition Troubleshooting Procedure