Texas Instruments 990 Manual page 129

N
I
N
........
0
<9:
-
Q )
-
( /)
~
-
< b
3
en
0
~-
c;;·
er
::s
Step
2
Symptom
Fails part 1 measure-
ment of video Full,
Blank, or H-Sync
pattern
Fails part 2; passes
part 3. Program
unable to write a
particular pattern
at location(s) with-
in a bank of networks
Table 2-10. Fault :Isolation Procedures for Apparent Memory Failure
Probable Cause
Defective memory
network(s). Read
data multiplexer.
Read data latches
memory control
logic
Trou~leshooting
Procedure
Perform parts 2 and 3 to
obtain more information.
Use CU verb to move
cursor to failing loca-
tion( s). Use CD-S to
verify failure mode.
Use CD-SL to estab-
lish scoping loop.
Normal Indication
See example.
If Abnormal
Proceed as in example.
Example:
1.
2.
3.
4.
5.
6.
7.
8.
Part 1 (El) failed. Video values not 0 (suggests memory picking up bits).
Part 2 (E2) failed. EXPECTED DATA ACTUAL DATA ACTUAL ADDRESS
30 32 17F
75 77 27F
(suggests picking up bit at lower memory addresses)
EXPECTED ADDRESS
17F
27F
Part 3 (E3) passed. Memory errors probably not caused by cursor address malfunctions.
Select verb CU-A. Set address to 17F
16 .
Select verb CD-S. Set data to 30
16
(ASCII 0).
Use CD-SL verb to establish scoping loop as symptoms indicate and data set to 301
6
(ASCII O).
If data read (30
16
)
and display is character 0 at cursor location, memory/CPU input register (figure 1-24) is probable cause. Sync on CURDQ
(Ul00-19) (U6-15 for 2nd controller). Check MlDlQ at U87-14 (U14-14 for 2nd controller).
If data read (30
16 )
and display is 2 at cursor location, check memory output MDOlQ at Ul06-S (U36-5 for 2nd controller). Data read
by program is data written to memory. Data on screen at current cursor location is data read from suspect location. MID, 0-7,
Q
contains
write data until cursor is moved, at which time it contains read data.