Main CPU firmware replacement
Changing the firmware may be necessary as upgrades become available. The firmware revi-
sion level for the main CPU is displayed during the power-on sequence. The firmware for the
main CPU is located in the EPROMs U156 (EVEN) and U157 (ODD), leadless ICs that resides
in chip carriers on the PC board.
To replace the CPU firmware, do 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 the paragraph entitled “Static sensitive
devices.”
3. Using an appropriate chip extractor, remove U156 and U157 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.
5. With the EPROM properly positioned, push down on the chip until it completely seats
into the chip carrier.
6. Repeat steps 4 and 5 for EPROM U157.
Disassembly 3-9
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