6-53
PMISCOUT U760 pin 2 (bit DO)is set to 1 which should unmask the WPDN that is already set true.
INTREG (bit 0) is tested for 1. If test fails, the test result is set to FAIL.
INTREG U654 pin 18 (bit DO)is tested for 0 and the test result is set accordingly.
A BUSTAKE is executed (previously tested), Interrupt Latch bit D2 is set true (WPDN) and PMISCOUT
Register U760 pin 2 (the mask for WPDN), is set to O.
Testing Method:
Miscellaneous Register A12U760 (schematic diagram 1):2190
MWPDN
3. Test that U750 pin 2 (FLD2) has a LO-to-HI transition on the second strobe. If there is no LO-to-
HI transition, replace U750. If there is, then test U854 pin 17 (schematic diagram 1) for the same
signal as at U750 pin 2. If present, replace U854; if not, find the open.
2. Run test 2180 in CONTINUOUS mode and check the clock line to A12U750 TVREG, pin 11
(schematic diagram 20) for LO-to-HI transitions. There should be two clock pulses under the
trigger strobe. If not, troubleshoot the clock source back through Decoder A12U884 (schematic
diagram 1) to isolate the problem.
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:
TVREG U750 pin 2 (bit DO)is then set to 1 and PMISCIN (bit D7) is tested. If the test fails, the test
result is set to FAIL.
TVREG U750 is set
=
00000000 and PMISCIN A12U750 pin 3 (schematic diagram 1) is tested for O.
The test result is set accordingly.
Testing Method:
Video Option Mode Register A12U750 (schematic diagram 20):2180
FLD2
4. Test that U754 pin 19 has a LO-to-HI transition on the third strobe. If there is no LO-to-HI transi-
tion, replace U754. If there is, then test A12U854 pin 15 for the same signal as at U759 pin 19. If
present, replace U854; if not, find the open.
3. Run test 2170 in CONTINUOUS mode and check the clock line to A12U754 at pin 11 for LO-to-HI
transitions. Since this is the register that provides the strobe to WORD TRIG, there should be four
clock pulses, one at each end of the trigger strobe and two under it. If not, troubleshoot the clock
source to isolate the problem.
2. Check that U754 pin 1 RESET is HI.
Now using CH2 probe:
Table 6-6 (cont)
Maintenance-2430 Service
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