6-56
If marked FAIL in the Extended Diagnostic menu, go to the next lower level of diagnostics and run
those tests to determine the problem register.
The remaining two tests use initialized data in U441 and U440 (display and readout memory will be
written with our standard four patterns in the first four bites of each memory).
The next three tests deal with the
"Q"
bus of the display state machine and require strobing of data
and shifting of bits for readout.
Running this test will test all the Display bus registers. There are seven tests in this section. The first
two write a pattern to one register and read back from another as in the previous section.
Display Memory Bus Registers:2300
TB-DSP
4. If 2 and 3 above are ok, then select a pattern test and check that the data lines are the same
states as the pattern; i.e., 10100101 would have the 07 pin
=
1, 06 pin
=
0, etc. If ok, replace
U531.
3. Check U530 pin 11 for clock pulse activity (WR strobe from System ILP).
2. Run test 2230 in CONTINUOUS mode and check U530 pin 1 for DISCON
=
LO during the time of
the trigger strobe. If not, troubleshoot the Register Select circuit (U550 and U450D) for proper
operation.
Using the CH 2 probe:
1. Set up the test scope as per Step 1 of the 2110 troubleshooting procedure.
If test
=
FAIL for all test then look for failure using the following steps:
Troubleshooting Procedure:
NOTE
The readback bit (bit 0) is the main board diagnostic bit and will not be tested.
If run from this level, all four tests are selected in turn, or one may execute anyone test by selecting
2231 to 2234. The test involves writing four unique patterns (see test 2200) to U530 and reading them
back from U531. The four patterns test for all stuck-at(s) and for lines shorted to other lines. By know-
ing which test fails and the bit pattern, one may easily determine a bus problem by observing which
bits are the same in the failed tests.
The DISCON (display control) register is two components, latch U530 and read-back buffer U531. The
test result is set to PASS, any failure sets it to FAIL.
Testing Method:
Display Control Register A11U530 and A11U531 (schematic diagram 17):
2230
DISCON
Table 6-6 (cont)
Maintenance-2430 Service
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