Tektronix 2440, User Manual

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Maintenance— 2440 Service
Table 6-6 (cont)
7. If ZON not present, troubleshoot the Z-Axis Logic circuitry, U223C and input gates and signals
(schematic diagram 17).
8. If all ok in the crt and Z-Axis circuitry, go to the "No Display" troubleshooting tree at the back of
this manual. Also, check that the Power-on Self Test completes without hanging. (See “ System
m
P Halts in Power-up Test” following “ No Intensity Control.”)
No Intensity Control
1. Check signal output of U227 at pin 13. Is the waveform correct (see waveform 145 on schematic
diagram 19), and does its amplitude vary with the DISP INTENSITY control? If yes, then check the
signal path components to the junction of C R442 and R546 for continuity.
2. If the signal at U227 pin 13 does not vary with the DISP INTENSITY control, check CR135 for
open or short.
3. Check the 21RT signal on pin 2 of U227. Does it vary correctly with the DISP INTENSITY control?
If yes, suspect U227. If no, then use the FORCE DAC test to verify the INTENSITY pot and the
DAC SYSTEM .
4. If the INTENSITY pot changes the DAC settings in the FORCE DAC test, the pot and pot­
scanning circuitry are ok; if not, troubleshoot the Front Panel.
5. Check the suspected DAC outputs at the points indicated in the FORCE DAC test table. If DAC
outputs are ok, troubleshoot Intensity multiplexer A10U811 (schematic diagram 6) and its select
signals, and the Z-axis signal amplifiers (A10U810 and A10U812). Troubleshoot DAC circuit if the
DAC outputs are bad (see the DAC System troubleshooting procedure).
i
6. Check the DISDN signal at U414A pin 6 and the PRESTART + DISPLAY signal at U323A pin 3
for correct operation (schematic diagram 17). If not correct, troubleshoot the Readout State
Machine (see the "No Display" troubleshooting tree at the back of this manual).
SYSTEM
m
P Test 3000— TRIG and READY LEDs on or Test 6000— READY and ARM LEDs on, and the 2440 Self
HALTS IN Test has halted.
POW ER-UP
TE S T Problem is probably in the Display State Machine circuitry (schematic diagram 17) or the DISDN signal
path to the System
pP
Interrupt circuit. Check that the DISDN signal is correct at U414 pin 6
(waveform 126 on schematic diagram 17); if not, troubleshoot the Display State Machine (see NO
DISPLAY troubleshooting chart in the “ Diagrams” section for typical Display State Machine
waveforms). If the DISDN signal is ok, check the DISDN signal path to U580 pin 4 for continuity.
Test 8000— plus ( + ) LED on and Self Test has halted.
1. "Running Self Test” message is displayed, but nothing else is occurring.
Check the ACQDN signal at A 11U670 (Time Base Controller).
2. No display is seen.
Check operation of the Readout State Machine.
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