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Maintenance— 2440 Service
Table 6-6 (cont)
2. Check that Q 107’s collector switches LO at the end of a step (should stay LO at end of
PAUSE'd step 1) and back HI when the sequence is restarted (push PRGM).
If the collector switches properly, the problem is an open component in the R107-
J125/P125-Flex Cable-J1904 path.
3. If collector doesn’t switch, either the transistor, its collector supply, or its base drive is bad
(CR107 may also be shorted). Isolate base drive to Q107 via R108 to determine whether the
drive or output circuitry is bad.
The drive signal comes from I/O register block of schematic diagram 1.
5
GPIB CAPABILITY AVAILABLE FOR EXTENDED DIAGNOSTICS
Extended Diagnostics test may be run via the GPIB interface to track down failed devices when the
Front Panel is locked up due to a front-panel failure or when there is no display visible. The importance
of this is that the initial step of locating all problem areas is simplified when the 2440 can do it itself.
1.
If the hardware and software are available to interface a 2440 to a GPIB controller, then run the
Extended Diagnostics test. Troubleshoot any failed diagnostics test as indicated in Procedure 7.
2.
If GPIB interface is not available, go to Procedure 6 to troubleshoot the display problem.
6
DISPLAY TROUBLESHOOTING
INTENSITY
No Intensity (HV Supply and CRT, schematic diagram 19):
If there is no GPIB capability, troubleshooting is going to be more difficult if no display is available. The
steps in this table address the analog problems not detectable by the Extended Diagnostics in any
case. Digital failures of the Display System are covered in the troubleshooting tables in the "Diagrams’’
section at the back of this manual.
1.
Press STATUS to set READOUT level.
2.
If no display is present, check the crt intensity grid voltage ( V I 000 pin 3), the grid bias adjust, the
crt cathode and heater circuits, and the crt anode HV.
W A R M I N G
A High Voltage probe is required to measure the grid, cathode, and anode voltage of
the crt.
3.
If no voltages are present, troubleshoot the HV power supply. The - 1 5 V Unreg supply is fused
by F961 (schematic diagram 23) which will be open if a component failure in the HV power supply
caused excessive loading.
4.
If crt voltages are good, and still no intensity, turn off the 2440 and check the crt heater for con
tinuity from pins 1 to 14. If open, change the crt.
5.
Does intensity vary with the Grid Bias Adjust? If not, troubleshoot the DC Restorer circuit. If it
does, check the signal from U227 at pin 13.
6.
Check input to U227 ZON on pin 3. If input ok, check supply voltages to U227. If all ok, change
U227.
6-47
Summary of Contents for 2440
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Page 136: ...Theory of Operation 2440 Service Figure 3 15 PWM Regulator and Inverter 3 94 ...
Page 138: ...Theory of Operation 2440 Service Figure 3 16 PWM switching waveforms 3 96 ...
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Page 423: ...2440 Service Figure 9 4b 2440 Block diagram part 2 6330 27 BLOCK DIAGRAM PART 2 ...
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Page 428: ...2440 Service WAVEFORMS FOR DIAGRAM 1 6 2 8 5 3 2 ...
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Page 432: ...2440 Service WAVEFORMS FOR DIAGRAM 2 BUS ISOLATED 6 6 0 3 4 9 ...
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Page 450: ...2440 Service WAVEFORMS FOR DIAGRAM 8 6603 27 ...
Page 455: ...W A V EFO R M S FOR D IAG RAM 11 WAVEFORMS FOR DIAGRAM 11 6603 29 ...
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Page 517: ...10 16 R E V J U L 1993 Replaceable Mechanical Parts ...
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