Diagnostic Testing and Troubleshooting
Calibration Failures
5
5-19
1. Check the three power supplies with respect to GND (A2TP3 or A2U1-42) on the
Display Assembly.
• VCC (A2U1-6) 4.85 to 5.35 V dc
• VEE (A2U1-19)-5.0 to -6.0 V dc
• VLOAD (A2U1-18)-28.5 to -32.0 V dc
2. Check the filament drive signals FIL1 and FIL2; these connect to the last two pins
on each end of A2DS1. These signals should be 5.0 V ac centered on a -25 V dc
level. FIL1 and FIL2 should be 180 degrees out of phase. If the dc bias of the
filament signals is not at about -25 V dc, the display segments that should be "off"
will show a shadowing (or speckling) effect.
Note
It may be necessary to disable the watchdog reset by jumpering A2TP1
(A1U5-3, A1U5-11) to GND (A2TP3) to verify the following items.
3. Check the clock signal at A2TP2. This signal should be 4.19 MHz
(.238 µs per cycle).
If the signal is not 4.19 MHz, the ceramic resonator, U2 is probably defective.
4. Check the state of the RESET signal (A2U1-1). This signal should be low once the
reset time is completed (after power-up).
5. Verify that the DISRX signal (A2U1-39) goes low after RESET (A2U1-1) goes low.
If this sequence does not occur, communication to the Main Processor is held off
with the DISRX signal high. If DISRX stays high but is not shorted to VCC, A2U1
must be faulty.
6. Verify activity for both the DISTX and DSCLK signals. These signals are driven by
the Main Processor and must be transitioning for the Display Controller to receive
commands from the Main Processor.
7. If all segments of a particular digit do not turn on at power-up, the grid drive from
A2U1 may not be connected properly to A2DS1. Grids are numbered from 0 to 10
(left to right as the display is viewed). For a digit to be enabled, the respective grid
drive signals (GRID(0:10)) must be at approximately VCC (4.85 to 5.35 V dc.) For a
digit to be disabled, the drive must be at VLOAD (-28.5 to -32.0 V dc.)
8. If a segment under each of several (or all) grids fails to be turned on (or off)
properly, one of the anode drive signals may not be connected properly from A2U1
to A2DS1. When an anode signal is at VCC, and a grid signal is at VCC, then the
corresponding segment on the display is illuminated.
9. If the Main Processor has difficulty recognizing front-panel button presses, the
switch scanning signals (SWR1 through SWR6, A1U6-21 through -26, respectively)
should be checked. When no switch contacts are being closed, the switch scanning
lines should have about 20 kΩ of resistance between each other (through two 10 kΩ
pullup resistors to VCC). None of the switch scanning lines should be shorted
directly to GND at any time, unless one of the switches is closed.
5-16. Calibration Failures
5-17. Introduction
Calibration processes for both front panel and computer interface operation are described
in Chapter 4 of this manual. Generally, a calibration failure is noted with an error beep
To Next Page
Loading...
