6-59
The test is to load a pattern into the display counters, U220 and U211, with the LDCOUNT strobe. The
counter outputs are switched to the a bus through U221, U212, U210 by holding U414A in the reset
mode (PRESTART + DISPLAY is LO). The inputs to U140 (lower half) are the bits 06 through 08
where 01 through 03
=
O.04 and 05 are the bOand bt data of the pattern. To read back properly,
one shifts the pattern left 3 bits and use bits 4, 5, and 6 of XDIAG (U243); the test result is set to FAIL
if the test fails.
The test result
=
PASS.
MISC
=
00100000. Significant bit is b5 (ZAXIS OFF).
MODECON
=
00001000. Significant bit is b3 (U140 lower half).
DISCON
=
01100000. Significant bits are b2, b5, b6, and b7 (STOPDIS, enable "a" bus, not
ENVELOPE mode).
Initialization:
This test requires the display state machine to be operative. There is no "good" way to insure that it is
functional and there have been no previous tests. Therefore, if this test fails, it could be for several rea-
sons other than U140.
If run from this level, all four tests are selected in turn, or one may execute anyone test by selecting
2341 to 2344.
Testing Method:
Readout Buffer U140 (diagram 16):
2340
U140
5. Verify the chip enable to U130 pins 1 and 15 is LO. If ok to here, replace U130.
4. Verify the outputs of U221, U212, and U210 are stable and correct after the LDCOUNT strobe to
the previous bus.
3. Verify that U323 pin 3 is LO.
2. Verify that after LDCOUNT strobe, that the outputs of U222, U220, and U211 are stable and of
the correct level for the test selected.
1. Run test 2230 in CONTINUOUS mode and verify the LDCOUNT strobe pulse at pin 11 of U222,
U220, and U211.
Now using the CH 2 probe:
Set up the 2430 test scope as in Step 1 of the 2110 troubleshooting procedure.
4. Ramp Buffer U130 (schematic diagram 16) may be defective.
3. Address Multiplexers U221, U212, and U210 may not be operating properly.
2. U414A may not be resetting, or U323 pin 3 might be HI due to a failure.
1. LDCOUNT might not be strobing the data into Display Counters U220 and/or U211 (schematic
diagram 17).
Table 6-6
(cont)
Maintenance-2430 Service
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