6-70
4. Check the data I/O pins of U431 (pins 9,10,11,13,14,15,16, and 17) for activity when test 3100
is selected. If no activity when DEY (output enable) is LO (pin stuck HI or LO), then suspect U322;
otherwise suspect U431.
3. Check for activity on the output enable line to U431 (DEY, pin 20). If none, work backwards and
find the problem.
2. Check for activity on the write enable line to U431 (WE. pin 21) and note that it is LO at the same
time as the chip select line. If no signal present, work backwards and find the problem.
Using the CH 2 probe:
1. Run test 3110 in CONTINUOUS mode and check for activity on the chip select line to U431 (CSY,
pin 18). If active, trigger the test scope on the signal. If no chip select, work backwards and find
problem.
Using the CH 1 probe:
If test
=
FAIL then look for failure and correct using the following steps:
Troubleshooting Procedure:
DISPLAY (VERTICAL) RAM A11U431 (schematic diagram 16):
3100
A11U431
The four tests may
be
executed from this level (3000) or from any of the nine sublevels (3100 through
3900), or any individual test may
be
executed by entering test number 3x10 through 3x40 (x
=
1
through 9).
Zero shifted right through a field of ones with decrementing address.
Zero shifted left through a field of ones with incrementing address.
One shifted right through a field of zeros with decrementing address.
One shifted left through a field of zeros with incrementing address.
3100 DISPLAY (VERTICAL)
2K U431
3200 READOUT (HORIZONTAL) 2K U440
3300 MAIN (SYSTEM) 2K
U668
3400 SAVE
2K
U350
3500 ATTRIBUTE
4K X 1 U430
3600 ACQUIRE
2K
U600
3700 CMD/TEMP
2K U440
3800 COEFF
2K U432
3900 NV (NONVOLATILE) 2K
U664
The RAM test is in four parts:
From this level, all nine RAMs are selected in turn. An individual RAM test may be run by selecting test
numbers 3100 to 3900.
All RAM tests are non-destructive. The first RAM tested is the Display RAM. It is then used, if good,
as a storage location for the contents of the other RAMs while they are being tested. The contents are
returned after the test is completed.
3000
SYS-RAM
Table
6-6
(cont)
Maintenance-2430 Service
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