6-64
2. Position CH 2 down to allow room and connect the CH 2 probe to U641 pin 1; save CH 2 into
REF2 and Display REF2. The LO TBSEL pulse should be coincident to a HI RD pulse; if not, then
troubleshoot the TBSEL or the RD signal line.
1. Run test 2410 in the CONTINUOUS mode. Set the Sec/Div setting of the test scope to 1
JLS
and
connect the CH 2 probe to pin 19 of bidirectional buffer U641 (TBSEL); save CH 2 into REF1 and
Display REF1.
Now using the CH 2 probe:
Set up the 2430 test scope as in Step 1 of the 2110 troubleshooting procedure.
Troubleshooting Procedure:
Running the test executes the Time Base Controller in FISO mode.
Time Base Controller A11U670 (schematic diagram 8):2410
U670 FISO
The test causes Time Base Controller U670 to simulate all the necessary states to get an acquisition
in Short-Pipe and FISO modes.
Running the test at this level will execute the Time Base Controller (U670) tests for Short-Pipe (SISO)
and FISO modes.
2400
TB-DSP
7. Replace U440.
6. Check that pin 21 of U440 (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 patterns 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 (DEX) and pin 18 (CSX) of U440 for a negative strobe coincident with the XSEL
strobe. If either is not present, troubleshoot U421 and the input signals to it.
4. If the input and output data patterns of U314 do not match, replace U314. If they match each
other, but are not correct, suspect a problem with Horizontal RAM U431. Run test 2371 through
test 2374 to see if all patterns fail. If all do not fail, troubleshoot for a bad bit of the failing test or
tests. A Word Recognizer probe would be useful for making these checks but is not necessary.
3. Check that the data pattern for the test is correct at the input and output pins of U314. The data
is stable during the XSEL 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.
2. Check for activity on the WRD signal line of U314 (pin 1); if no activity, check for open back to
A12U564 (schematic diagram 2).
Using the CH 2 probe:
1. Run test 2370 in CONTINUOUS mode and check U314 pin 19 for a negative strobe XSEL at
10
JLS
from the LO-to-HI transition of the trigger pulse. If not present, troubleshoot U323 and the
inputs to it.
Table 6-6 (cont)
Maintenance-2430 Service
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