Chapter 4 Assembly Level Troubleshooting 75
3. If after replacement of the (A5) Outguard Controller assembly the
instrument is still inoperative, the logic circuitry on the Outguard
Power Supply (A6) assembly may be causing the failure. Go to the
Assemblies Removal/Installation Procedures in Chapter 3 of this
manual to replace the Outguard Power Supply (A6) assembly.
Isolator Failure
For isolation logic failures, the message "ISOLATOR FAILURE' will be
displayed after the power-on self-test is completed. The instrument then
locks up and no front panel/remote control is possible. Either the inguard or
outguard isolation logic can cause the failure. Do the following:
1. Use the Covers Removal/Installation procedures in Chapter 3 of this
manual to remove the instrument's bottom cover and bottom shield.
2. Turn the instrument on. Go to the Power Supplies troubleshooting
procedures in this chapter of the manual to check both the inguard and
outguard power supplies.
3. If the power supplies check good, the failure can either be on the
Outguard Power Supply (A6)assembly or the A/D Converter and
Inguard Logic (A3) assembly. These assemblies can cause the failure
since the isolation logic circuitry is on both assemblies and the
self-test is unable to differentiate between the failures on the two
assemblies. ln addition to these, the (A5) Outguard Controller
assembly could also cause the failure. However, most failures will
most be caused by the A3 or A6 assemblies.
4. Try replacing the Outguard Power Supply (A6) assembly first. Go to
the Assemblies Removal/Installation Procedures in Chapter 3 of this
manual to replace the assembly.
5. If after replacing the Outguard Power Supply (A6) assembly the test
still fails, try replacing the A/D Converter and Inguard Logic (A3)
assembly. Go to the Assemblies Removal/Installation Procedures in
Chapter 3 of this manual to replace the assembly.
6. If after replacing the Outguard Power Supply (A6) assembly the test
still fails, try replacing the (A5) Outguard Controller assembly. Go to
the Assemblies Removal/Installation Procedures in Chapter 3 of this
manual to replace the assembly.
RAM Failures
These failures show up when the checksum of either the RAM or the
Calibration RAM is incorrect. If a failure occurs, a message indicating that
the checksum is incorrect will be displayed. Since both RAMs are located
on the Outguard Controller (A5) assembly, replace that assembly for any
RAM failure. Use the Assemblies Removal/Installation Procedures in
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