If you use an Apple ][ you've probably noticed that the clock setting and your Control Panel settings are lost whenever the power is turned off. That's because these settings are stored on a volatile SRAM chip, which requires power to retain data. When the computer is turned off this power is normally supplied by a lithium battery on the motherboard. The battery lasts a relatively long time, as the drain is small–on the order of microamps (µA) or less–but nevertheless, it does run down eventually, and after so many years it's more likely than not to be completely dead. This Instructable will show you how to replace it.
---IMPORTANT NOTE: This procedure is much more complicated than replacing the battery in a modern system. Please read through the entire Instructable before starting. Also, this repair is designed to meet the original factory specification for this computer. If you just want to change the battery–and don't mind slightly changing the appearance of a rarely-seen area inside the computer–then there are much simpler options. See "Alternatives" at the end of this Instructable.
Step 1: Supplies
–Your Apple IIGS (duh…)
–Replacement battery, 1/2AA, 3.6V, axial leads. (Tadiran TL-5101/P)–Digi-Key, www.digikey.com, P/N 439-1003-ND
–Soldering iron, 20-40 watts, fine tip–Radio Shack
–Solder, 60/40 tin-lead–Radio Shack
–Desoldering bulb, wick, or pump–Radio Shack
NOTE: DON'T substitute other battery types. Most seemingly similar batteries (even with the same nominal voltage) won't work properly, may damage your computer and could even pose a fire hazard.
Step 2: Getting Started
Shut down the computer, and disconnect all external cables (power, peripherals, etc.) If you use the internal game port or legacy interface cards this will mean opening the top. Place the unit on a table where you can work comfortably, and make sure you have good light.
The components are very sensitive to static electricity, so use an antistatic wrist strap or floor mat connected to a good ground.
Gather all your tools and materials.
Step 3: Disassembly
Remove the cover. You already know how to do this–just push in the locking buttons located on either side of the back of the case, and pull up gently on the cover. Take your cards out–yes, ALL of them. Write the slot number on each one so you can put them back later! Then disconnect all of the wires (power, the internal speaker, and the fan if one is installed) and take out the power supply. It is released by carefully pushing back the plastic snap tab and swinging the front of the power supply up. Some of the wire connectors have small plastic locking tabs–be sure to release these.
Now we need to remove the motherboard. (Phew. Remember what I said about complexity?) The battery is, as you can see, located beneath the power supply, but we need to access the underside of the board to remove it. Turn the machine over and detach the front panel by carefully pushing back the three large plastic tabs, marked with yellow arrows in the picture. Turn it right side up again, and unfasten the board by applying SLIGHT upward pressure and carefully pushing back the seven small plastic tabs shown with red arrows, starting at the front. The board simply swings up towards the back and slides out.
Step 4: Replace Battery
Desolder the old battery and remove it, being sure to note the polarity. (It should be marked on the board, but check first to make sure the print is legible.) Be careful not to apply too much heat to the board or you will damage it. Dispose of the battery properly.
Bend the leads of the new battery to match the spacing of the holes. Make sure the holes are clean, then insert the leads of the new battery. Make absolutely sure the polarity is correct BEFORE touching the leads to the holes, and do not allow them to brush against anything else while doing this. Remember that the battery is supplying voltage even during the installation process and an improper connection could burn out components on the motherboard.
Solder the new battery into place, again being careful not to overheat the board. Make certain you do not create any solder bridges, either. Trim the leads close to the solder, making sure the tool does not cause a short circuit to any other connection.
Step 5: Reassembly
This is fairly straightforward but it's easy to forget something along the way, so follow this procedure closely.
Snap the motherboard into the case by first aligning the connectors on the back edge with their respective holes, then hinging the board down and carefully snapping it into place. Avoid bending the board or using excessive force, and check to make sure all of the tabs are engaged. Then snap the front panel into place, making sure the speaker wires are properly routed under it. Snap the power supply into place, and reconnect the internal wires (power, speaker, and fan). Reinsert your cards in their respective slots. (You did number them, right?) Snap the cover back on.
You're almost done!
Step 6: Setup and Test
Reconnect the assembled unit to your workstation as it was before. Then power on with the OPTION key held down to run the system self test. If all is well a series of intriguing colors and patterns will flash on screen for a while, followed by a musical tone and the words "SYSTEM GOOD" displayed in the corner of the screen. Now you can restart and set your clock and Control Panel preferences. If everything goes well they'll still be there the next time you power up!
Step 7: Alternatives
If the preceding procedure seems too complicated there are two other practical options:
1. Instead of desoldering the original battery, simply cut the leads close to the battery, and twist the new leads onto them. It's best to solder the connections but not actually required as long as they are twisted securely. Just be careful not to put too much stress on the connection between lead stub and board. The advantage of this method is that the board need not be removed from the case–you need only take out the power supply, in order to access the battery. As a cautionary note, make sure the battery sits flat on the board and that the twisted connections do not protrude above the top of the battery. Otherwise they might short out against the metal case of the power supply.
2. Use either of the above procedures to install a 1/2AA battery holder, and buy the version of the cell without leads. This makes it easier to replace the battery in the future.
Other hacks, such as using a different battery or adding some other type of standby power supply and dispensing with the battery altogether are beyond the scope of this Instructable and are not recommended unless you are very familiar with this computer, your intended power source and electronics in general, but in that case you wouldn't need the Instructable in the first place, now would you?
Also, make no attempt to connect a new battery (or other power supply) without first removing the dead battery. Doing so will cause reverse charging and is hazardous.
Technically there is one more option, and that is to just live with it and not do anything. But as a perfectionist myself I wouldn't consider that much of an option :)
Hope you liked what you saw and feel free to comment!