152 Chapter 7
Troubleshooting the Processor, Power Supply, and Display
Verifying the A26 CPU Assembly
CPU Assembly Detailed Troubleshooting
There are a few items that should be checked before suspecting a
defective CPU assembly. The CPU must have all the DC power supplies
coming from the motherboard. Carefully measure the DC supplies on
the motherboard at the N12 and P12 test point pads. The test points
are located near the digital IF connector. These two supplies come from
a regulator circuit on the A25 Motherboard.
Also measure the VCC and VDL supplies by inserting the E4406-60021
extender board into option slot 2, next to the digital IF assembly.
Measure VCC (+5.2 V) and VDL (+3.4 V) using DCOM for the ground
connection. VCC and VDL voltages come from the A5 Power Supply.
If the power supplies measure correctly, and the CPU does not boot
properly, the I/O lines could be loaded down by another assembly, or a
clock signal could be missing. Remove the A7 Digital IF assembly and
try rebooting. The A8 Analog IF assembly must be installed and
providing the 30 MHz sample clock before the CPU will boot. See page
150 for troubleshooting hints.
If the instrument will still not boot, suspect the A26 CPU assembly is
faulty.
Battery Information
The analyzer uses a Lithium Polycarbon Monofloride battery to power
the instrument clock/calendar and to backup the NVRAM on the CPU
assembly. If the power cord has been disconnected for several hours,
and then the power cord re-connected and the instrument powered up,
the first sign of a depleted battery is the on-screen time and date read
out are incorrect. The date reverts to 1970. Also, you may see the
message “Restoration of NVRAM” on the display status line. This
message occurs when the contents of NVRAM do not match data stored
on other assemblies, and this results in the NVRAM being updated.
The battery is located on the CPU assembly. See A26BT1 in the
Replacement Parts section of this manual. To replace the battery, it is
necessary to remove the CPU assembly. Refer to Chapter 11 for removal
procedures.
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