Video (Signal) Only
If only the video information is incorrect, suspect A4 IF Section, A3A8, or A3A9. To
eliminate the IF, connect the rear-panel SWEEP and VIDEO RECORDER OUTPUTS to an
oscilloscope. If the video is correct, then either A3A8 or A3A9 is defective.
Remove cable 96 from
A3A9J1.
Then jumper A3A8TP1 to A3A9TP3 and push Instrument
Preset. This substitutes the sweep ramp for the video input. The CRT display is similar
to Figure 7 in the A3A8 tab. If the ramp is incorrect, remove A3A9, jumper A3A8TP1 to
A3A8TP6 and push Instrument Preset. The CRT display is the same as Figure 7 in the
A3A8 tab. If the display is correct, the problem is in the A3A9 assembly. Refer to A3A9
Troubleshooting procedure. If ramp is incorrect, suspect ADC on A3A8. See the A3A8
Troubleshooting notes to verify this.
Don’t rule out the sweep system, especially the ramp converter on A3A8, when
troubleshooting video failures. Some ramp converter failures produce CRT displays that are
similar to those caused by ADC failures.
All CRT Information Blank or Distorted
Check X, Y, and Z DISPLAY OUTPUTS on rear panel. If these are correct, the fault is most
likely with the X/Y Deflection Amplifiers or Z Axis Amplifier (or A1A2 XYZ Deflection
Amplifier). The following program, which places a dot at the center of the display, is helpful
when troubleshooting the Deflection Amplifiers. It balances the voltages in both halves of the
circuitry. Press Instrument Preset and key in the following:
Blank Trace A, fsHirT), Recorder Lower Left, 0 Hz DSPL ADRS
(SHIFT
K
Recorder Upper Right WRITE
1090 Hz Vector Command
512
Hz X coordinatesforcenter screen
512 Hz Y coordinates for center screen
If the X, Y, and Z DISPLAY OUTPUTS produce either distorted or no output, Digital
Storage must be tested. Connect a jumper from A3A6TP3 to A3A6TP6 and push A3A7S1.
The Digital Storage Test Pattern (Figure 1 of the A3 Digital Storage Troubleshooting tab)
results. Refer to the Digital Storage Troubleshooting procedures. If the test pattern is correct,
start with the system ROMs check.
If the test pattern is incorrect, verify operation of A3A3 Line Generator and A3A2 Intensity
Control. Refer to the troubleshooting information included with the schematics. If A3A3 and
A3A2 are working properly, then all of Digital Storage will have to be checked, starting with
A3A6.
Whenever the display is blank, and the left INSTR CHECK LED is off, check the A1A6
±15 V Regulator (or A1A6 High Voltage Power Supply) and A1A7 +100 V, +5.2 V
Regulator. The power supply LEDs indicate the presence of voltage but not regulation. Verify
operation of A3A2 Intensity Control and A1A2 Z Axis Amplifier. If these are all working
properly, carefully examine the A1A3 High Voltage Regulator assembly.
If the CRT is blank, check the CRT oscillator to see if it is turned off. Measure A1A6TP6
with a DVM. If TP6 is a digital high, the CRT will not operate since the oscillator is turned
off. Troubleshoot A1A6 to check for bad components, shorts, and so forth. If the A1A6 is
operating correctly, check the CRT disable line from A4A9U14. If the IC is damaged, it
2 Al
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