PowerBook 520c Restoration - Battery Rebuild
I recently purchased a used PowerBook 520c at an auction. It was described as "powers on", so I had no idea if that meant it would boot up or the power light works. Fortunately, it booted up and appeared to be fully functional.
The PowerBook 500 series introduced several new features. It had the first touch pad, replacing the track ball. It had a 68040 processor but lacked an FPU. The 520c had a color passive matrix display. Not as clear as an active matrix display, but for the time, not shabby. It also came with two battery ports so you could double your battery life.
The NiMH cells in the battery had long given up and probably contained nothing but potassium hydroxide powder. You can find refurbished batteries online. But the company I checked out did not have good reviews and the cost was prohibitive. I decided to rebuild it myself after reading this thread.
Materials
I used the Tenergy 9.6V Flat NiMH Battery Packs for RC Cars found here at Amazon (https://www.amazon.com/gp/product/B001BA292A/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1). My thought was that it would be easier than having to solder tabbed cells together myself. It contains eight AA size cells with tabs soldered together.
You'll also need solder, a soldering iron, X-acto knife, insulating tape, nerves of steel...
Teardown and Rebuild
Sorry, I don't have photographs. I will probably be doing this again so I have another battery to double my untethered time.
I stripped the shrink wrapped plastic shell from the batteries. It was obvious to me they wouldn't fit still wrapped in the plastic. And the Tamiya connector was useless.
The outer end cap of the battery pulls off if you pull up along one of the long sides. It will feel as if you are about to break it when it comes free. I also carefully removed the battery contact cover from the opposite end. This will slide off if you lift the tab slightly.
I cut the battery housing apart using an X-acto knife to score the plastic along the seam between the housing halves. I took my time and made small cuts in an effort to avoid cutting any cells or the EMM board.
If you place the battery with the EMM board facing away from you with the battery contacts to the right (image above), the cells in the battery are arranged in series, starting at the top left negative end soldered to one end of the ribbon cable with six cells until you reach one end of the fuse. The other end of the fuse then connects to the remaining two cells that are flipped around from the orientation of the first six cells. I cut the ribbon cable from the cells by cutting the tabs off the cells leaving them soldered to the ribbon cable.
To use the Tenergy cells, I was required to clip the last two cells free, turn them end over end, and solder the fuse on so it had the same orientation as the original cells. Then I soldered the ribbon cable to the new cells using the tabs still attached to the ribbon cable.
Once I had the cells and fuse together, I attempted to drop them into the battery housing and found that they were slightly longer (1 or 2 mm) and of a smaller diameter than the original cells. I was able to cut away enough of the internal supporting structure from both halves of the housing to make room for them to fit - but just barely.
Reassembly was pretty tight. The Tenergy cells had carboard insulating on the ends of the cells that I had to remove and replace with insulating tape. The end cap goes on straight instead of rotating off. You need to use a fine point (I used a paper clip) to compress the spring in the battery latch while you push the end cap back on. The battery contact cover just slides back on.
I used freeware software package named EMMpathy. The software was designed specifically to recondition batteries on PowerBook 500 series It reported the EMM memory as corrupt and the battery would not charge. What little charge it had started to dissipate. However, someone suggested that I check the power adapter. I hadn't realized it had two lines, one for the laptop main power and a second for charging the battery. Sure enough, my power adapter had a bad battery line. I found a tested replacement on Ebay, the batteries charged and discharged just fine. I was able to get nearly 2 hours of charge from the one battery I have.
Here's a time lapse video of it discharging.
