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Try replacing
U20
and U42
PALS
first, then try replacing U39 and
U40
ROMs. If I/O
failure still occurs, probe I/O lines with oscilloscope.
Level
2
Manual
Tests
If the Self Test doesn’t lead to a failed component, it will be necessary to use a DVM or an
oscilloscope. The following procedure may help locate the failed component:
a. Check all power supply voltages that supply power to the Al5 Controller.
b. Check processor clock by connecting oscilloscope to
A15TP2-4
(CK). The clock frequency
should be approximately 7.36 MHz. The amplitude should be approximately
+5
V (HIGH)
and 0 V (LOW).
Al
so
check for LCLK at pin 7 of A15U27B.
c. Check HP-IB clock at pin 5 of A15U27A. The HP-IB clock frequency should be
approximately 3.68 MHz. The amplitude should be approximately
+5
V (HIGH) and 0 V
(LOW).
d. Some intermittent failures may require the use of heat (hair dryer) or cold (freeze mist) to
isolate the failure.
Caution
Care should be exercised to avoid getting components too hot. Excessive heat
may cause permanent damage of good components. Also, avoid spraying freeze
mist directly on PC boards. Failures due to high-resistance paths between
traces on PC boards have been caused by spraying the boards with freeze
mist.
6 Al5