These were great batteries, 40 years ago.
This was a good task to start on. It’d been years since I’ve done any serious electronics work, and my previous Arduino project, while successful, reminded me just how much I’d forgotten about electronics over the years. And my skills had mostly vanished too. So a nice easy project was just the thing.
About those batteries. They were amazing things back in the day. But when I opened the battery pack, it was revealed that they’ve done what all batteries do over time. Run out of charge and leak. The corrosion wasn’t as bad as it could have been and the plastic package was in great shape — but the circuit board in the battery pack was beyond hope.
First step was to remove the resistor and the connector. A few minutes with a hot soldering iron and some desoldering braid did the trick. Then clean the contacts and leads with some CLR, followed by a good rinse and they’re ready to be used on the new board.
I had some old perfboard / prototyping board available so it was a rather simple thing to carve out a new one with a Dremel tool cutting disk. *PROTIP – CUT PERFBOARD OUTSIDE. THIS STUFF STINKS!!*
Then, rebuild the simple circuit to match what was on the original board. The power connections (Left (-), Right (+)) will be made when I solder the battery pads to the board.
If you look closely at the resistor, you’ll notice that I cracked the ceramic(?) coating and some chipped off. Since I had some replacements on order (though not the exact value so I’d be linking three in series) I figured ‘what the hell? If it doesn’t work, I’ll just do the series thing’.
But before soldering it on, I did test it and the value matched what it should be according to the NEC PC-8201a Service Manual. So maybe I won’t have to do the ‘series thing’.
The batteries in the NiCad pack weren’t meant to be replaced, so they were soldered together in series to form the 4.8V package. My goal was to make the batteries replaceable, which means I needed to fabricate the connections.
Rather than ordering the parts from eBay or wherever, and them taking 30-60 days to arrive, I managed to salvage the springs and plates from some dead solar-powered sidewalk lighting units.
They were a bit big, but I had some tin snips and they were soon cut down to size. Then run the Positive and Negative leads, a little solder and some stripped solid-core cat5 strands to make the serial connections, and the battery pack circuit was complete.
Having the resistor in the circuit makes our 4.8V pack into a 5.5v pack, which is within the input voltage range of the PC-8201a. The standard, non-rechargable, AA battery pack that was available for the unit didn’t have the resistor, and regular AA cells are 1.5V so that x4 gets you a nice, tidy 6V input voltage.
Next up, a good wash up to clean off 40 years of grime!