The first job then was to see what I’d got and what state it was in. Like many portable computers the HX-20 has an internal battery pack and these are prone to failure and if the cells leak they can make a complete mess of the internals. It’s clear that the previous owner was very far sighted, as the original cells had all been removed. They were in the case though and showed clear evidence of leakage – I shudder to think what would have happened if they had been left inside:
An oddity of the HX-20 is that whilst it has an external power socket (and my examples comes with the original Epson branded power supply) this is actually for a battery charger. So whilst it will power up if connected, it doesn’t work properly (neither the printer nor the tape drive function) and the voltages are all over the place. If you use it like this for any period of time it’s not going to do it any good at all and would probably cause some damage eventually. The battery forms a vital part of the power system and therefore a new pack is needed for everything to work.
The original pack is made up of ‘sub-C’ cells, which I’d not come across before but which are commonly used in rechargable battery packs. The original pack had a capacity of about 1000mAh. It is fortunately very easy now to get hold of cells of all sizes from various online retailers.
The battery connects to a two pin header on the main board, and fortunately the original connector was still intact. The original pack was a sealed unit, but I made a replacement by buying tagged cells. The positive and negative wires were soldered to tags on two of the cells, and the other two arranged in series to make a complete battery. There was just enough room for everything to fit snugly:
The new pack has a much larger capacity and I imagine it would run for a very long time, even with the printer and the cassette in use. It’s definitely more than enough for my needs. The charging circuit is also very rudimentary, and the manual suggests various formulae for calculating the charging time. There is no automatic shutoff or anything clever like that, so you do need to be careful about how long you charge it for.
So now we have power, and the computer boots up fine and is perfectly usable. So the next thing was to look at the tape drive. After the battery pack, this should be easy…
Universal Discovery Methodology 