6-54
It run tram this level, all tour tests are selected in turn. One may execute any single test by selecting
2211 to 2214. The test involves writing tour unique patterns (see test 2200) to U532 and reading them
back trom U540. The tour patterns test tor all stuck-at(s) and tor lines shorted to other lines. By know-
ing which test tails and the bit pattern, one may easily determine a bus problem by observing which
bits are the same in the tailed tests.
The MISC register is two components; latch U532 and read-back buffer U540. The test result is set to
PASS and the test is done; any tailure sets it to FAIL.
Testing Method:
Misc Registers A11U532 and A11U540 (schematic diagram 17):
2210
MISC
NOTE
DISCON (bit 0) will not change, as it has the main board diagnostics as its input.
Test 4-00101101 is sent and read back. Test result is set to fail it not a match.
Test 3-10010110 is sent read back. Test result is set to fail if not a match.
Test 2-01001011 is sent and read back. Test result is set to fail if not a match.
Test 1-10100101 is sent to the input latch and read back via the output buffer. Test result is set to
fail if not a match.
Running the test from this level will test all the Display Control registers. These tests will utilize four bit
patterns to detect faults. If marked FAIL at this level, go to the lower levels in the menu to test for the
failed register. The four bit patterns sent in each of the register tests are as follows:
Testing Method:
Display Control Registers (schematic diagram 17):2200
TB-DSP
3. Check that U550 pin 2 has a LO-to-HI transition on the second clock pulse. If bad, change U550.
If ok, store in REF1 and display it while testing output of A12U880 pin 6 (schematic diagram 1). If
ok then replace U654; if not, check the inputs to U880 on pins 4 and 5, and if those are ok,
replace U880.
2. Run test 2190 in CONTINUOUS mode and check that A12U550 pin 1 COMREG (schematic
diagram 2) is set LO during the period that the clock line U550 pin 9 has a LO-to-HI transition.
This may
be
done by saving the COMREG signal in REF1 (if using a 2430 as the test scope) and
displaying it while acquiring the clock pulse on U550 pin 9. If these signals are not coincident, then
troubleshoot the cause.
Now using the CH 2 probe:
1. Set up the test scope as per Step 1 of the 2110 troubleshooting procedure.
If test
=
FAIL then look for failure using the following steps:
Troubleshooting Procedure:
Table 6-6 (cont)
Maintenance-2430 Service
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