3. Using a thin-bladed screw driver, pry the plastic PC board stop (located at the bottom of
the display board) until the bar separates from the casing. Pull the display board from the
front panel.
4. Remove the switch pad by pulling it from the front panel.
Main CPU firmware replacement
Changing the firmware may be necessary as upgrades become available. The firmware
revision levels for the main and front panel CPUs are displayed during the power-on sequence.
(The main firmware revision level is displayed on the left; the front panel firmware revision level
is displayed on the right.) For example, REV: A01 A02 indicates a main firmware revision level
of A01 and a front panel firmware revision level of A02.
The firmware for the main CPU is located in the EPROMs U156 (EVEN) and U157 (ODD),
leadless ICs that reside in chip carriers on the PC board. To replace the CPU firmware, perform
the following:
WARNING Disconnect the instrument from the power lines, and remove the test leads
before changing the firmware.
1. Remove the case cover as described earlier in this section.
2. Locate U156 EVEN and U157 ODD (EPROMs) on the main PC board. They are the
only devices installed in chip carriers (sockets).
CAUTION EPROMs U156 and U157 are static-sensitive devices. Be sure to follow the
handling precautions explained in Static sensitive devices.
3. Using an appropriate chip extractor, remove U156 from its chip carrier.
4. Position the new U156 EPROM on the appropriate chip carrier. Make sure the notched
corner of the chip is aligned with the notch in the chip carrier.
NOTE Be sure to install the correct EPROMs at the ODD and EVEN locations. The
instrument will not function if the EPROMs are installed in the wrong sockets.
5. With the EPROM properly positioned, push down on the chip until it completely seats
into the chip carrier.
6. Repeat steps 3 through 5 for EPROM U157.
7. After installation, make sure the instrument powers up normally before replacing the
cover.
Disassembly 5-7
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