Omron 8025G Maintenance Manual page 129

MAINTENANCE AND REPAIR
SECTION 6
In such cases, you can often narrow a problem down to one or two possibili-
ties by thoroughly analyzing the symptom.
For example, assume there is no beep response. Table 6-1 indicates that
the Cursor Control, Refresh Buffer, Keyboard or Speaker could be at fault. Your
aim should be to eliminate as many choices as possible by determining which cards
are probably not at fault. Here is a typical elimination procedure:
1. Two audio indicators--beep and click--are used in the terminal. Is the
click response operating?
2. (Assume click is operative) The "Click response inoperati vet. entry in
Table 6-1 potentially eliminates the Timing Control, Refresh Memory, and
Processor Cards and brackets the problem to the Cursor Control and Re-
fresh Buffer cards. (Note that the Refresh Buffer is not related to the
click response.)
3. Before replacing either the Cursor Control or Refresh Buffer, however,·
determine the probable operating status of the other three cards. Re-
view the Theory of Operation and schematics in this manual to establish
which signals on the three cards are directly or indirectly related to
both the click and the beep circuits. Such a review will reveal that
both audio indicators are related in some manner to
TJiD,
WAIT and MAS-
13.
4. In the absence of other symptoms that might relate to
TJiD,
WAIT, and
MAS-13 (e.g., input/output problems), Step 3 established a high proba-
bility
t~at
the Timing Control, Refresh "temory, and Processor Cards are
not at fault.
S. The choice is now narrowed to two: Cursor Control and Refresh Buffer.
Since the Refresh Buffer is the easier card to replace (no interconnect
cable to disconnect), it is the logical first choice for replacement.
If you need to take fault isolation beyond a field replaceable part, bench
maintenance is recommended (see paragraph 6.3).
6-6