6-65
There is one diagnostic bit for readout off the main board and that is the logic-AND of the MSB of all
the shift registers. The shift registers are preset to 10100101, or 1010010110100101 and the diagnos-
tic bit is tested to see if a "1" is being read out for the MSB. If the diagnostic bit is not
=
1, then
either one of the registers is not loading or the diagnostic bit is stuck. In any event, no further mean-
ingful data is possible, so the test stops. If initialization is successful, each bit is shifted out, register by
register, and compared against what it should be by shifting the initial pattern and comparing the MSB.
After any register is tested, it is reinitialized so the next register may be tested. Discon (input
=
U531
pin 18, output
=
U531 pin 17) is the diagnostic bit from the main board.
From this level, the initialization and all five tests are selected in turn. An individual test may be run by
selecting test numbers 2510 to 2560.
The MAIN board has five Shift-register tests. These are in two groups. The first group includes Gate
Array U270, Peak-Detector U530, Attenuators U511 and U221 (acting as one 16-bit register), Trig
U140. The second group has the System-DAC U850 and U851 (acting as one 16-bit register).
2500
MAIN
6. If all checks were ok, suspect A12U542 (schematic diagram 2).
5. If present, test for the square wave at U680 pin 16 and replace U680 if missing.
4. Test the output of U670 at pin 26 for a square wave signal (TIMER) with a period of about 200
"'s; if not present, replace U670.
3. Position the CH 2 display down to allow room and probe U641 pin 11 through 18 while REFl sig-
nal is LO and REF2 signal is HI. Compare the results to 01000000 where U641 pin 11 is D7 and
U641 pin 18 is DO.If they do not compare, replace U641.
2. Position the CH 2 display down to allow room and connect the CH 2 probe to U641 pin 1. Save
CH 2 into REF2 and display REF2. The TBSEL pulse should be coincident to a HI RD pulse; if
not, then troubleshoot the chip select or RD signal line.
1. Position the trigger strobe (CH1) near the top of the crt and connect the CH 2 probe to pin 19,
TBSEL, of U641. Adjust the Sec/Div setting of the test scope to 1 us. Verify that there is a nega-
tive TBSEL pulse during the positive trigger strobe. Save the CH 2 waveform in REFl and display
REF1.
Now using the CH 2 probe:
Set up the 2430 test scope as in Step 1 of the 2110 troubleshooting procedure and run test 2420 in
the CONTINUOUS mode on the 2430 under test.
Troubleshooting Procedure:
Time Base Controller All U670 (schematic diagram 8):2420
U670 SISO
6. If all checks were ok, suspect A12U542 (schematic diagram 2).
5. If present, test for the square wave at U680 pin 16; replace U680 if TIMER signal is missing.
4. Test the output of U670 pin 26 for a square wave with a period of about 200
",S.
If not correct,
replace U670.
3. Position CH 2 down to allow room to display the signal and probe U641 pin 11 through 18. While
the REFl signal TBSEL is LO and REF2 signal RD is HI, compare the results to 01100101 where
U641 pin 11 is D7 and U641 pin 18 is DO.If they do not compare, replace U641.
Table 6-6
(cont)
Maintenance-2430 Service
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