NEC PC-8201a Adventures – Part Two: Rebuilding the NiCad Battery Pack

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!

NEC PC-8201a Adventures – Part One: It’s here, now what?

Back in the early-to-mid ’80s, personal computing was finding it’s way. Desktop computers were becoming more visible in smaller businesses, but the work of computing still had to be done at the workplace. Portable computers were really just shrunken down desktops — they were called luggables at the time. Then came the revolution, as they say.

My first glimpse of the new wave of portable computers was not the Radio Shack (Tandy) TRS-80 Model 100, but rather the NEC PC-8201a – a sibling to the Model 100 (and the Olivetti M-10). All were made by Kyocera of Japan and based on the Kyocera Kyotronics KC-85. But the 8201a was the first portable I used that was actually a reasonably competent computer for it’s time.

Radio Shack TRS-80 Model 100
Kyocera Keytronic-85

Olivetti M-10

Costing about $1,000 ($2,600 in 2021) USD for a 24K model (yes, K as in kilobyte), it was a solid mobile computing platform with simple text editing, built-in telecommunications, and the BASIC programming language; supposedly the last iteration of BASIC that Bill Gates worked on before he went on to do other things.

Add a cassette recorder to your ensemble, and you could save your documents to tape, or load in other financial analysis and calculation programs. Plug it into a modem and you could dial in to CompuServe or GEnie, or a BBS (Bulletin Board System) and be charged by the minute for your online social media (we didn’t call it that back then) or gaming activity.

Fast Forward — about 40 years

Perhaps I’m getting to that age where the past begins to develop a rich, warm glow. I discovered that you could still find these portable computing pioneers available for a modest sum on Ebay. And with my recent interest in IoT (Internet of Things) devices, and microcontrollers (Arduino, Raspberry Pi), it seemed like this could be an interesting way to pass some Pandemic time.

I found one for a reasonable price and a few weeks later was the happy owner of the little unit in the image at the top of this story.

They’re really simple (by today’s standards) little devices. After unwrapping it and waiting for it to warm up — it was delivered on a -15c day so I thought I’d give the electronics time to clear any condensation — I flipped the power switch. And nothing happened.

To be expected actually. The Ebay seller had used an external power supply to test it, so I had to cobble one together myself to actually get it running. 5xAA alkaline batteries and a salvaged battery holder from one of my Arduino projects got me the power I needed to turn it on. Instant gratification! It worked, no smoke leaked out.

Testing and next steps

I put it through a quick test, loaded basic, ran a ‘Hello World’ program, made it beep, typed on all the keys, and gave it a good visual inspection.

Since the unit didn’t power up without an external power source, I knew I’d be taking apart the removable, rechargeable NiCad battery pack. So I did that next.

As expected, the pack was shot. Corrosion had crept across the circuit board and the battery pack didn’t look good. I was going to have to rebuild that pack and circuit board if I wanted to use rechargeable in it. Excellent, an excuse to research!

After determining the state of the battery pack, I built a list of things to do, and started checking them off. I’ll leave the list below, but the details, well those are words for another blog post.