Service manual

30
SYMPTOM 3
Corrupt video display or characters
a)
Cause of Trouble
- 5v absent
Check Point
1 If -5v is absent - check for short at J12
(monitor o/p) of video board - or repair open
circuit. The -5v is generally shorted to 0v at
this point.
b)
Cause of Trouble
Faulty Video Ram
Check Point
Check for pulse on pin 2 of Video Ram.
Check for signal on P14 of any Video Ram.
Repair Method
1 Systematically disable the Video Rams by
earthing pin 14. Continue with this process
until corruption has reduced. The IC
with the least corruption when earthing, is
likely to be faulty...replace. See warning on
page 31.
2 If the corruption is very bad scopeing pin 14
MTX Service Manual