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11. Install the Control/Display Unit by reversing the steps followed in Section 3.2.1. Gently slide the CDU onto the
two Main Board connectors (J100 and J102), observing proper pin alignment during the process.
12. Connect the battery pack wiring harness to the 3-pin locking connector (J800) on the Main Board (see figure12).
13. Install the top and bottom covers by reversing the steps followed in Section 3.1.
SECTION 4
SERVICE AND TESTING
4.1 MEMORY BATTERY REPLACEMENT
The GPS 155 utilizes a built-in lithium battery to maintain user waypoints/settings stored in RAM.
This battery has an operational life of up to five years. Should the battery require replacement, as indi-
cated by the “Memory battery low” message, disassembly of the unit will be required to access the bat-
tery clip.
When replacing the memory battery, all user waypoints/settings may be lost. If this occurs the message
“Stored Data Lost” will be displayed. The unit must then be attached to an antenna, allowed to search the
sky and collect new almanac data before it will be usable again. This process may take 20-30 minutes.
1. Remove the covers as described in Section 3.1.
2. Remove the Control/Display Unit as described in Section 3.2.1.
3. Remove the four screws (211-50202-15) and spacers (233-00012-00) which secure the RF/IF Assembly to the
Main Board.
4. Carefully pull the RF/IF Assembly upward, disengaging it from the Main Board Connector (J803) Place the RF/IF
Assembly to the side of the unit. (NOTE: With the mounting screws removed, the cover for the RF/IF Assembly
will be loose. Grip the RF/IF Assembly firmly by the sides, instead of by its cover, when lifting upward.)
5. Remove the old battery by gently pushing it toward the back of the unit and out of the battery clip. A tuning tool,
or similar flat-tipped instrument, may be used to aid removal of the battery, but EXTREME CAUTION should be
exercised to prevent damage to the Main Board.
6. Immediately install a new battery (positive side up) into the battery clip.
7. Secure the RF/IF Assembly to the Main Board using the four screws (211-50202-15) and spacers (233-00012-00).
8. Install the Control/Display Unit by reversing the steps followed in Section 3.2.1. Gently slide the CDU onto the
two Main Board connectors (P501 and P502), observing proper pin alignment during the process.
9. Turn the GPS 155 on.
10. Press ENT to accept “NORMAL” mode operation.
11. Press ENT again to accept the Database Page.
12. Verify that the “Memory battery low” message does not appear on the Message Page by pressing the MSG key.
13. Turn the GPS 155 off and carefully turn the unit over.
14. Verify that the memory battery voltage (from test point to ground, see Figure 6) is at least 2.9 VDC.
15. Install the top and bottom covers by reversing the steps followed in Section 3.1.
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