Tektronix 2440, User Manual

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Maintenance— 2440 Service
Table 6-6 (cont)
Using the CH 2 probe:
1. Run test 2370 in C O N TINUO US mode and check U314 pin 19 for a negative strobe XSEL at
10
ns
from the LO-to-HI transition of the trigger pulse. If not present, troubleshoot U323 and the
inputs to it.
2. Check for activity on the W RD signal line of U314 (pin 1); if no activity, check for open back to
A 12U 564 (schematic diagram 2).
3. Check that the data pattern for the test is correct at the input and output pins of U 314. 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 W D bus.
4. If the input and output data patterns of U 314 do not m atch, replace U 314. If they match each
other, but are not correct, suspect a problem with Horizontal RAM U 431. 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 W ord Recognizer probe would be useful for making these checks but is not necessary.
5. Check pin 20 (DEX) and pin 18 (C S X) of U 440 for a negative strobe coincident with the XSEL
strobe. If either is not present, troubleshoot U421 and the input signals to it.
6 . Check that pin 21 of U 440 (W E) 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 W E signal is not correct, troubleshoot U422
and the input signals to it.
7. Replace U440.
2400 Running the test at this level will execute the Tim e Base Controller (U 670) tests for Short-Pipe (SISO )
TB-DSP and FISO modes.
The test causes Tim e Base Controller U 670 to sim ulate all the necessary states to get an acquisition
in Short-Pipe and FISO modes.
2410 Time Base Controller A 11U 670 (schematic diagram 8):
U670 FISO
Running the test executes the Tim e Base Controller in FISO mode.
Troubleshooting Procedure:
S et up the test scope as in Step 1 of the 2110 troubleshooting procedure.
Now using the CH 2 probe:
1. Run test 2410 in the CO N TINU O U S mode. Set the Sec/Div setting of the test scope to 1 ps and
connect the CH 2 probe to pin 19 of bidirectional buffer U641 (TBSEL); save CH 2 into REF1 and
Display R EF1.
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 R EF2. The LO TBSEL pulse should be coincident to a HI RD pulse; if not, then
troubleshoot the TBSEL or the R O signal line.
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