GE MAC 800, Service Manual

Page: 58 / 122

4-8 MAC™ 800 2031504-159D
Maintenance
Replacing the Real-time Clock (RTC) Battery
The RTC4574 has an internal 32.768KHz crystal unit. Serial
communication between the CPU and RTC4574, through the I/O port of
the CPU, exchanges time and date information between the CPU and
RTC. The RTC will not drift by more than 320 seconds per year. When
the device is turned on with AC power, the RTC is powered by +3.3 V
supply. When the device is turned off, the RTC battery powers the RTC
to keep track of the time and date. The battery is a 3V Lithium Ion coin
battery with 1000mAH capacity, which can sufficiently supply the clock
for a minimum of 5 years (worst case calculation). In the normal case, the
functioning period is assumed to be more than 10 years.
NOTE
Always use an anti-static wrist strap while opening the MAC 800
unit to avoid possible damage due to static electricity.
1. Remove the Mainboard Assembly as instructed in “Removing the
Mainboard Assembly” on page 4-16.
2. With the display connector at the top and facing upwards, locate the
RTC battery BT on the right side of the Mainboard.
3. Remove the four translucent plastic droplets.
4. Pull up the battery and cut the visible leg of the battery, keeping
enough of the leg on the Mainboard so that you can desolder and pull
off the broken leg with pliers.
NOTE
The ground leg of the battery is connected to a huge ground path,
which makes desoldering this leg difficult.
5. Desolder the other leg and pull it off the battery with the leg from the
Mainboard.
6. Remove the battery.
7. Turn the Mainboard Assembly over and desolder the two battery
contact sites.
NOTE
Dispose of the battery according to local municipal waste
guidelines.
8. Remove the solder pin with a Solder tool.
9. Solder the new battery into position on the Mainboard.
Check the polarity before soldering.
10. Turn the Mainboard Assembly back and add the four translucent
plastic droplets on the battery.
11. Reassemble the Mainboard assembly as instructed in “Reassembling
the Mainboard Assembly” on page 4-18.
12. Adjust the time and date.