Category Archives: Retro Computers

Epson PX-8 Battery Rebuild

After checking and rebuilding the battery for the Epson HX-20 (see the link at the bottom of this post), I then decided to check the battery packs in the two Epson PX-8 computers that I have.

These were both in poor condition and needed to be replaced. This got me thinking of all the old retro computers out there that are slowly getting destroyed by leaky batteries. So if you have one of these computers buried in a wardrobe, garage or attic; please take it out and check its battery, as if you leave it too late, the battery acid just may corrode the main PCB to a state that makes it beyond repair.

Neither end of these batteries are in useable condition. I’m not going to open them, I am just going to bin them responsibly (local shops take in old batteries) and build new battery packs. If you don’t want to build them, you can purchase from several online suppliers.

After about an hour of repeating the same process that was used when making the new battery pack for the HX-20, I now have a new battery pack for the PX-8. Only one more battery pack to build, but I need to get a couple more of the 2/3 C Cell rechargeable batteries, to complete the last pack.

At least the connector was not as damaged as the connector on  the HX-20 battery pack. So now I have a good battery pack that can be used when I start the repair process on the PX-8 computer.

HX-20 Battery Pack Rebuild 

HX-20 Battery Refit

After searching through my part bins, I was able to find a contact that I fitted into the connector for the battery pack, to replace the contact that was corroded. I fitted some spacers between each of the cell, then wrapped the battery pack in some tape to seal it.

Once the pack was assembled, it was fitted back into the HX-20. While reassembling the computer, I spotted a dry joint on the DC jack. So once again I disassembled the computer to remove the main PCB.

Once the PCB was out, I removed the DC jack, cleaned the contact for the DC jack, cleaned the pads on the PCB, reassembled the computer and tested it. The computer beeped when it was powered on, but I got no text on the LCD. So scratching my head, I disassembled the computer and checked the connectors. They all looked good. Then I remembered that the computer may need to be reset, as the battery had been out of the laptop for a few days.

So while the LCD was not showing anything when powered on, I remembered that you need to press “CTRL & @” to initialise the computer. After entering in a dummy date time of “01010101101” and pressing “Enter”, the computer reset and the LCD became active.

Yeah, the battery has been replaced and the computer is working again. 👍

Replacement Battery Pack for Epson HX-20

After disassembling the HX-20 the other day, and discovering that the Ni-Cad battery pack is leaking after 35 years,  I purchased some 2/3 C size cell rechargeable batteries. I purchased a total of 10 of these cells, as I plan to make a new battery pack for the HX-20 and one for a Epson PX-8’s that I also have. I suspect that if the batteries in the HX-20 are in this state then the ones in the PX-8 are not far behind.

Blog Post showing the teardown of HX-20.

Here is a link to these batteries on Amazon for those of you who want to replace their batteries in the computer.

After verifying that they were the correct size, I started to break apart the old battery pack to see how far gone  the batteries were. If you’re doing this at home, lay out some newspaper and wear gloves, as battery acid is nasty stuff.

Once I removed the yellow plastic shrink wrap from the battery pack, it was very clear that the protective foam on the negative side of the battery pack terminal was saturated (battery acid) and the terminal was corroded.

When the protective foam was released the lead to the negative side of the battery pack just fell off. It obviously hadn’t had a solid connection to the negative battery terminal for a long while.

Just to see how far the corrosion had gone, I cut into the wires going to the connector for the main PCB. I was unable to find any good clean tinned or copper wire – it was tarnished all the way to the connector. This means that I need make up a new connection going to the main PCB (I may just replace the headder  to the main PCB with PCB molex headder and replace the connection on the battery pack).

Curiosity got the better of me and I removed the last of the red shrink wrap on the old battery pack, just to see how bad the batteries were. The walls of two of the batteries were paper thin and were corroded in places completely. In fact I found two holes in the battery shells which are visible above. Can you spot them?  These batteries had seen better days and I was very happy that there were getting replaced.

It was very easy to wire up the new batteries. I just had to tack solder the positive lead of one cell to the negative lead of the other cell in series. Next step is to organise some spacers for in-between the cell, so the casings don’t short together, then to wrap the cells and install back in the computer.

– [Batt1] +  – [Batt 2] + – [Batt 3] + – [Batt4] +

We just have 4 x 1.2V Cells in series giving 4.8V. Once I get the new connectors for the battery pack and the main PCB. I’ll re-fiit the battery pack back in the HX-20, charge it up  and start testing.


Tandy TRS80-4P

Just over a year ago my brother-in-law came across a Tandy TRS-80 Model 4P computer with some floppy disks (5.25″). After a quick check, it was determined that the power supply was faulty. It’s since been removed from the computer and is currently sitting on my workbench, waiting to be repaired (yet another retro computer project that I haven’t started).

Epson PX-8 Repair (very soon)

A while ago I got two EPSON PX-8 portable computers, and over the  next while I’m going to attempt to get both of these machines operating, as neither of them are at the moment (for one reason or another).


After the recent post for the HX-20 Battery pack, I have organise to build a new battery pack of one of these two PX-8 computers.