6-71
4. Check the data I/O pins U350 (pins 9, 10, 11, 13, 14, 15, 16, and 17) for activity when test 3400 is
selected. If no activity (stuck HI or LO) when output enable is LO, then suspect buffer U352; oth-
erwise suspect U350.
3. Check for activity on the output enable line to U350 (WRD, pin 22). If no activity, work backwards
and find the problem.
2. Check for activity on the write enable line to U350 (WRR, pin 27) and note that it is LO at the
same time as the chip select line. If no activity, work backwards and find the problem.
1. Check for activity on the pin 20 chip select line to U350, and trigger the scope on the signal if
active. If no chip select, work backwards through the Chipselect circuitry and find problem.
Using the CH 1 probe:
Select test 3410 and RUN CONTINUOUSLY.
If test
=
FAIL then look for failure and correct, using the following steps:
Troubleshooting Procedure:
SAVE RAM A12U350 (schematic diagram 2):
3400
A12U350
If the System RAM data bus, chip selects, or output enable lines are defective, the processor system
will not function and the Kernel tests will need to
be
executed to isolate the problem. Therefore if the
RAM test fails, the most likely problem is U668. See Procedure 8 for the Kernel test.
MAIN (SYSTEM) RAM A12U668:3300
A12U668
4. Check the data I/O pins U440 (pin 9, 10, 11, 13, 14, 15, 16, and 17) for activity when test 3210 is
selected. If no activity (stuck HI or LO) when output enable is LO, then suspect U314; otherwise
suspect U440.
3. Check for activity on the output enable line U440 pin 20. If none, work backwards and find the
problem.
2. Check for activity on the write enable line U440 pin 21, and note that it is LO at the same time as
the chip select line. If none, work backwards and find the problem.
Using the CH 2 probe:
Using the CH 1 probe:
1. Check for activity on the chip select line U440 (CSX, pin 18, and trigger the scope on the CH 1
signal. If none, work backwards and find problem.
Run test 3210 in CONTINUOUS mode.
If test
=
FAIL then look for failure and correct using the following steps:
Troubleshooting Procedure:
READOUT (HORIZONTAL) RAM A11U440 (schematic diagram 16):3200
A11U440
Table
6-6
(cont)
Maintenance-2430 Service
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