6-37
4. Check for a fast ramp that corresponds to RAMP and RAMP from U370. This ramp should rise
from the stabilization level to a maximum and start down at the same time that the ST ART1 (or
START2) pulse steps high, and that the STOP1 (or STOP2) pulse steps high when the descending
ramp crosses 0 V. If not, troubleshoot the circuitry to determine the problem. These ramps should
be linear both in rise and fall times.
3. Make sure that the signal at the collector of 0491 and 0390 stabilizes at about 800 mV. This is
the baseline stabilization circuit. The waveforms shown next to the schematic diagrams are useful
to make waveform comparisons.
With the test scope:
2. Set the test scope to 500 p_s/div.
1. Connect a probe from CH 1 of the 2430 under test to the 4C test point on its main board. Select
REPET, set the 2430 under test to 5 ns/div and obtain a stable trigger.
ANALOG SECTION TROUBLESHOOTING
Now connect the EXT1 to U752 pin 1 and EXT2 to U752 pin 19. The input-output pairs may now
be checked, and they should compare at the "T" of the trigger point.
EXT1 A-B
500 mV
- (minus)
NORMAL
EXT2
TRIG AFTER; EXT ClK OFF
TRIGGER
A TRIGGER SOURCE
A lEVEL
SLOPE
MODE
B TRIGGER SOURCE
MODE
CH 1 and CH 2
DC
2V
Traces to graticule center
VERTICAL
MODE
COUPLING
VOlTS/DIV
POSITION
500ns
B
HORIZONTAL
A and B SEC/DIV
MODE
5. Check that the inputs to U752 are gated to the outputs of U752. The only time they are the same
is if both pin 1 and 19 are low. If a WORD trigger probe is not available, the following setup may
be used making use of the A and B Trigger Mode to obtain coincident triggering.
4. While triggering on the ST ART1 pulse, check for activity (fast to slow) at the Jitter Counter (U852
and U853) outputs (pins 3, 4, 5, 6, 11, 10, 9, and 8). Observe that each output pin on the ICs
should be switching slower than the preceding one as the counters count down. Replace the
counter if found defective.
3. While triggering on the ST ART1 pulse, check for gated signal (by STOP1) at U852 pin 1. Check at
U853 pin 1 for gated signal while triggering on the START2 pulse. If either gated signal is missing,
check the gating components to locate the problem.
2. Check that STOP1 and STOP2 are present at U841 pin 12 and U841 pin 12. These signals are
not coincident and should be jittering with respect to one another.
If missing, backtrack to U490 and/or U390 (diagram 12) to locate the defective component.
Table
6-6
(cont)
Maintenance-2430 Service
To Next Page
Loading...
