6-63
Set up the 2430 test scope as in Step 1 of the 2110 troubleshooting procedure.
Troubleshooting Procedure:
If contents of 2803h not equal to 00101101, then test result
=
FAIL
If contents of 2802h not equal to 10010110, then test result
=
FAIL
If contents of 2801h not equal to 01001011, then test result
=
FAIL
If contents of 2800h not equal to 10100101, then test result
=
FAIL
Set test result
=
PASS.
If run from this level, a" four tests are selected in turn, or one may execute anyone test by selecting
2371 to 2374. The contents of the first four bytes of U314 have been written and wi" now be tested
against the values that were thought to be written, any failure to match will cause that test to fail.
U314 is decoded by reading address 2800h.
Testing Method:
Horizontal Buffer (diagram 16):
2370
U314
7. Replace U431.
6. Check that pin 21 of U431 (WE) is HI during the HI portion of the trigger strobe (displayed on
CH 1 of the test scope). The data writes of the test pattern's occur during the LO portion of the
trigger strobe, and that activity can be seen. If the WE signal is not correct, troubleshoot U422
and the input signals to it.
5. Check pin 20 (DEY) and pin 18 (CSY) of U431 for a negative strobe coincident with the YSEL
strobe. If either is not present, troubleshoot U421 and the input signals to it.
4. If the input and output data patterns of U322 do not match, replace U322. If they match each
other, but are not correct, suspect a problem with Vertical RAM U431. Run test 2361 through
test 2364 to see if a" patterns fail. If a" do not fail, troubleshoot for a bad bit of the failing test or
tests.
3. Check that the data pattern for the test is correct at the input and output pins of U322. The data
is stable during the YSEL strobe on pin 19, and the data bit level must be read in coincidence with
it as other activity is also taking place on the WD bus. A Word Recognizer probe would be useful
to make these checks, but it is not necessary.
2. Check for activity on the WRD signal line of U322 (pin 1); if no activity, check for open back to
A12U564 (schematic diagram 2).
Using the CH 2 probe:
1. Run test 2360 in CONTINUOUS mode and check U322 pin 19 for a negative strobe YSEL at
10
IlS
from the LO-to-HI transition of the trigger pulse. If not present, troubleshoot U323 and the
inputs to it.
Set up the 2430 test scope as in Step 1 of the 2110 troubleshooting procedure.
Troubleshooting Procedure:
Table
6-6
(cont)
Maintenance-2430 Service
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