Troubleshooting Epson HX-20s

[James Harland]

Hello everyone,

I bought my first Epson HX-20 about 20 years ago on a flea market in Berlin, and it has been in a cupboard since it stopped working in January 2020. Recently I bought another HX-20 on the local equivalent of eBay, and now have the project to get one or both of them up and running, possibly mixing and matching parts from each to end up with one working model.

So far I ascertained that HX-20 #1 had leaking batteries, so I took them out and wired up 5V via a USB adapter to the 4.2 V input off the batteries, and got some reasonable results - I was able to get to the "garbage menu" fix it with CTRL + @ (in fact CTRL + § as #1 is localized to German), and even get into BASIC, but I could not actually write any BASIC, as only half the keys worked. So I started trying to clean and reseat the keyboard ribbon cables, though I found them to be in a terrible state. I think I might have broken something when I wanted to clean the plastic ribbon connectors with contact solution, as after doing that I got very strange display output, and after that the unit has not responded to power on. That might be due to a dodgy power swtich though, I need to look into that.

HX-20 #2 has had different issues. The batteries (which seem to be the original ones) charged OK, again I got the garbage menu. I was able to reset it with CTRL+@ (UK model this time), but only by hitting enter at an opportune moment, as when I pressed 1 I got an endless stream of 1s. However, I was not able to choose BASIC or Monitor from the menu, as the keyboard seemed unresponsive after this. When I dismantled it, the keyboard ribbon cables seemed in much better condition than in #1, but I cleaned them anyway (not attempting to clean the plastic connectors until I have a more precision way of applying contact cleaner). The inside of the computer was very dusty though, so I physically cleaned the inside with a static-free cloth, took apart the keyboard, washed the keys and function key membrane, and cleaned under the keys with a soft tootbrush and some spirit. I did use contact cleaner on the inside of the keys, which incidentally have a different mechanical structure to the #1. The next step is to reconstruct the keyboard once everything is thoroughly dry, and reconnect all the ribbon connectors, and see if I can get into the BASIC or Monitor.

So that's where I am at the momnent. I am very much a beginner to computer repair, and to electronics generally. I have built an RC 2014, and replaced a ZX Spectrum keyboard membrane, those are my only achievements so far.

I wonder if I might find people in this group who can advise as I go ahead with this project? I am in touch with Fred Jan who made this HX-20 website but I don't want to bother him too much with my beginner questions.

Thanks and all the best,

James

[James Harland]

So an update: HX-20 #1 is still displaying random lines of screen display if it even switches on. That's OK though as HX-20 #2 is working great after the keyboard overhaul. I've run a program on BASIC, and the first routine in Leventhal's 6800 book (though I had to change the addressing mode, and so the commands as addresses 40 and 41 are not available). It's very convenient how the HX-20 automatically displays the contents of all registers when it returns from a routine.

Neither cassette drive is working - no big surprise there. I think the printer on #1 might still work, and it is certainly cleaner than the one in #2, so I might swap them out. 

I think both machines might have an issue with the on/off switch, #1 when switching on, and #2 when switching off.