Oki ML490 Maintenance Manual page 133

A
Yes Are ALE, PSEN, RD, WR, signals as specified in Figure C-6?
Yes Are (T1) SELECT and (INTO) BUSY signals low level?
Yes Are +9V and -9V input to Q1?
Yes Is pin 1 SSD signal of Q3 High level?
Yes Is pin 11 SSD of Q1 low level?
Yes Is the RxD of Q3 as specified in Figure C-7?
Yes Replace the Q3.
42114101 Rev.1
180ns
ALE
PSEN
271ns
RD/WR
No Replace the Q3.
No Check Q3 on the Control Board.
No Replace defective component in +9/–9 volt control circuit.
No Replace the Q3.
No Replace the Q1 or the CN1?
RxD
ST bit
SSD
No Replace the Q2.
542ns
542ns
Figure C-6
Figure C-7
5V
0V
5V
0V
5V
0V
5V
0V
SP bit
5V
0V
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