Through the Repair Cafe project I’ve been running I’ve been asked about all sorts of things which has led to some interesting projects. Just recently, a friend brought me a Honeywell CM927 central heating controller which had been causing trouble.
This appears to be a very commonly installed device, with a battery-powered wireless control unit linking back to a powered relay at the boiler. There do seem to be various issues with them, one of which is a problem with the connection with the screen resulting in a corrupted display. However, this was different – the screen was fine, but some of the keys were poorly responsive and the screen would regularly blank out for a few seconds when trying to set the time or date. This often happened when trying to get the ‘OK’ button to respond which needed several presses.
I found a useful Youtube video which describes a fix for the screen issue (which didn’t apply) but which does give useful instructions for opening the casing and getting the PCB out:
My first thought was that this was something to do with the power supply, so perhaps a problem with the contacts on the batteries. The faulty buttons were probably due to a poor contact between the button.
The internals are very simple – just a screen, a few chips and a relay and the buttons.
The square pads with the interlocking pattern are the contacts for the buttons. The rubber button in the top casing pushes down, and the back of the button has a conductive surface which bridges the two sides of the contact. Several of these – particularly where the ‘OK’ button connected – were dirty and so I cleaned them up with isopropyl alcohol to give the best chance of a good contact.
On the back of the rubber buttons there was a rough surface which is conductive, and on testing them the ‘OK’ button showed almost no conductivity at all. This is a common fault with TV remotes are other device which use this design, and the solution is to renew the surface using conductive paint. I found something suitable on Amazon and painted the back of the OK button with it.
The two large square contacts on the bottom left and right of the board are where spring connectors from the battery make contact. Looking closely at them, I could see two small holes on each pad where it appears that the springs have worn through the pad. I was pretty confident that this was responsible for the cutting out, due to the power momentarily being interrupted. I flowed some solder on to the pads to restore the connection, and also bent out the springs slightly.
On reassembling everything I was pleased to find that the buttons now worked correctly, needing only a gentle push and there was no more cutting out. So overall a great result for a relatively small effort!
At the most recent Repair Cafe a friend asked me about a wireless subwoofer for a soundbar which was not working. It was completely dead with no signs of life.
On closer inspection it proved to be a Sony HT-CT290 soundbar (which was working fine) and a separate SA-WCT290 subwoofer.
It’s common especially when things are completely dead that the fault lies in the power supply, which often relatively easy to repair (bad capacitors or similar issues). So I was hoping to find something similar here. A bit of quick searching around revealed this to be a relatively common fault with a voltage regulator which steps the 18V down to 3.3V for the control circuits.
Getting access to the circuit board is fairly easy, just a question of removing all the screws on the back of the unit. The PCB is fixed to the rear panel, and there are two cable connectors to unplug from the main board (one for the LEDs and one for the speaker). Then it’s quite easy to see what’ going on:
The large brown PCB is the main power supply board, and the green one has the rest of the supporting circuits. This board steps down the 240V AC to 18V DC. With the board powered up it was possible to check the voltages at various points as outlined in the service manual. The 18V seemed to be getting through OK which ruled out any problem with the brown board.
The chip circled in red on the green board is a TPS54334 step down voltage converter (sometimes called a DC:DC or buck converter) which is a general purpose device but in this case is set up to reduce the 18V input to 3.3V output for the low voltage circuits. The service manual suggests measuring the voltage at one of the connectors, but for some reason neglects to mention the two large ‘test pads’ just next to it (on the left of the red circle in the picture above). The service manual states that if the voltage is anything other than 3.3V to replace the board.
On the one I had, the voltage was 2.90V – so not much lower, but definitely not 3.3V and actually more than 10% out of tolerance. Other people have reported the output as being 0V, but given that the reading was clearly wrong it seemed logical to start there. This chip is a surface mount device and unfortunately I don’t (yet) have the kit or the skills to rework this. There’s a great video where someone does just this:
So I was contemplating doing this, but then I came across an interesting thread on iFixit which describes a similar problem and solution. However, further down the thread comes the genius idea to ignore the SMD work completely and replace the part with a separate buck converter board (which are widely available very cheaply) with the input 18V taken from the power connector (first three pins), and the output 3.3V fed into the test points described above. Rummaging around in my junk box I was delighted to find just such a module left over from an old project, in this particular case based on an MP1584 chip:
These converters all work in the same way, in that you feed an input voltage in one side and then adjust the small screw to set the output voltage. This particular one has a tiny and very sensitive screw, and after connecting it up to an 18V source it took quite a lot of very fine adjustment to get it to output exactly 3.30V.
It was then simply a matter of wiring the input to the 18V supply pin on the power connector (I used pin 1) and the output to the test pads (the positive one helpfully labelled ‘+’). The ground is all commoned together so I only wired in one negative lead. I stuck the module to a spare piece of board with a ‘sticky fixer‘ and secured the leads with tape. I also took the precaution of snipping off all the leads of the old IC although I didn’t actually remove it. This is hard to do as it has a big blob of solder on the back holding it to the board for heat dissipation.
With the board powered up, all the voltages looked good so it was a matter of putting everything back together and looking for signs of life:
I was very pleased to see a green light appear – and everything appeared to be working properly. Not having the actual bar I could not test it myself, but the owner later reported that it was back to full working order which was very pleasing.
Once again, a relatively complex piece of electronics was defeated by a simple power supply problem and the generous provision of test points made it very easy to replace. SMD devices are a pain for a casual hobbyist like myself, although it is now getting cheaper and easier to obtain the kit to work them it’s still a whole lot more difficult. Overall though, a great result and this does appear to be a very common problem with this model. There are also reports of the same thing happening in the soundbar itself.
Let me know in the comments how you get on if you attempt something similar
I’ve recently started a ‘Repair Cafe‘ in my local church. As hopefully is clear from other articles on here I love finding out about how things work, and fixing them when they break. This is good both for my own personal satisfaction, but also it’s good for society at large in terms of reducing waste and saving resources. I’ve also really enjoyed meeting people through it and being able to help them.
At the most recent event, someone brought in a Lakeland Dry:Soon clothes airer. These are quite expensive items, and it arrived looking brand new and still in its box:
However, in spite of the immaculate appearance, it didn’t work. When you plugged it in, the display flashed on and off and there was a constant beeping sound.
Having a quick look around the Internet it appears that this is a common problem – on various forums people were complaining about it, and whilst some were lucky and were able to get their items replaced by the supplier, many others were told that nothing could be done and they should buy a new one which feels like a bad deal for all concerned, and a real waste.
On closer examination these rails are very simple devices, with one small control panel which switches a heater in the rail itself. The behaviour of the panel was strongly suggestive of a problem in the power supply circuit – it is obviously starting up OK (showing ‘on’ on the display and beeping) but then something is going wrong and it’s resetting. I’ve seen this sort of thing before where the power supply is inadequate causing the circuit to reset over and over again.
Getting the control panel out was relatively easy. The first thing to do of course is disconnect everything from the mains. The panel is held in by two screws at the back of the panel, so remove these and you can pull the module out. Turning it over you’ll see three small screws which hold a plastic cover, so remove these too and take the cover off. You’ll then see the underside of the circuit board and you can pull the board out of the plastic housing.
The next thing to do is disconnect the three wires. The outer two are the mains power supply (live and neutral) and the middle one is the output to the heating elements. It’s important to label the wires before you disconnect them. They are ‘FASTON‘ or blade connectors and they have a metal retaining tab which makes them hard to pull off. The best way is to use a very small flat screwdriver to push into the connector and this will release it and then it should pull off easily.
You can now get a good look at the circuit board:
It’s a pretty simple device – the main components are displayed above. On the other side of the board there is a microprocessor which runs the timer and controls, and some additional components to bring the voltage down from 240V and convert from AC to DC. The relay is marked ’24V DC’ and is clearly used to switch the heating elements on and off. I measured the voltage at the output of the rectifier, and it was showing only about 5V which is clearly not enough to switch the relay and confirmed the suspicion that something was wrong.
I did not know a huge amount about how these circuits worked as traditionally you’d have a transformer to reduce the voltage down (in this case from 240V to 24V). However after some reading I identified this as a ‘transformerless power supply’:
The link gives lots of detail, but in essence the key component is the ‘X2 capacitor’ which is the yellow rectangular component above. If this fails, then nothing will work properly. They often do fail, and when repairing vintage computer or audio equipment I have frequently found old ones to have exploded and generated a lot of smoke and a horrible smell.
I also found an article about a similar timer / control board where the X2 capacitor proved to be responsible:
I decided to try replacing it. Fortunately these are cheap and readily available. The original one is marked 0.39uF at 275V. It’s also important to note the physical dimensions when looking for a replacement to make sure it fits properly as there is not much additional space on the board. The pitch (ie distance between leads) is 15mm. I looked everywhere and I could not find a 0.39uF part which would fit, but plenty at other ratings. The exact rating of these components is not critical (especially voltage, which must not be any lower but can be higher) so I ended up buying a 0.47uf at 315V version instead on eBay, for the princely sum of about 31p each (when buying 10).
Replacing the part is a simple soldering job – desoldering and removing the old and replacing and resoldering the new one. I was pleased to find that the new one was absolutely identical in size and appearance to the original and it was easy to solder in to place.
So then it was simply a question of reassembling and testing. I connected the wires, switched on and…
Success! I could hear the relay engaging, and the display is clear and steady with no beeping to be heard. There a few odd things which on reading the manual are by design – the main ‘on / off’ switch lights up, but only when the heating element is off – apparently to remind you that you to press it. On fully reassembling the unit I was pleased to find that it now all works perfectly.
I shudder to think how many of these have been consigned to the tip because of such a simple and easily remedied fault. It’s likely either a design fault, or perhaps a bad batch of capacitors but either way I feel that the supplier could do better than telling people it’s not repairable and that they need to buy another one.
So if you have one of these with this problem – I’d definitely encourage you to consider attempting the repair (or finding someone to help you with it). If you have a local repair cafe or similar then the information in this post should allow them to help you with it too.
Please do let me know in the comments if you have experienced this or if you want any help.
So the next thing to do was the strip the unit down and look for the culprit. As stated above service manuals are readily available these days (I found mine here) and I was able to find the right one on archive.org. Service manuals are strange things – having seen quite a few now they are very variable in how much detail they give, and whilst obviously they are aimed at people who are supposed to know what they are doing the variation is quite puzzling. So this particular one is very helpful although does miss a few specific points which I’ll describe here.
It’s a complicated beast
The disassembly diagram shows a couple of ways to remove the mechanism – in view of the complexity of the device there are two separate circuit boards as well as the mechanism itself. You can either remove the main board, and then the mechanism, or else the whole ‘mechanism deck and main board block’ together. The latter of these is what you need to change the belts… but I didn’t realise this until too late and did the former. It doesn’t really matter but does mean removing more screws and connectors than you actually need.
Secondly and most importantly the manual does not tell you the whole story about the flexible ribbon cables of which there are two. The manual simply shows that they need to be removed (CN303):
So I just pulled them out, assuming that they were the variety that were held in by friction rather than any kind of locking mechanism. However, when I came to put it back together again I could not work out how to push them back in again. The cables were very floppy and despite a lot of effort I could not get them to engage in the sockets. I was beginning to get worried as I could see there was a high risk of damaging the cables and being left with a completely non-functional unit.
After a lot of messing around and getting nowhere I finally had an insight when I realised that the ends of the ribbons were completely floppy and not rigid at all – so were obviously designed to work with a locking connector. Looking closely at the connector I realised there were two black tabs, and these could be eased forward which released the clamp. Once this was done it was simple to slide the cable back in and close the clamps again. I really did have a lucky escape here, both when removing the cables and fruitlessly trying to push them in again. Other Sony service manuals clearly explain how the connectors work so it’s frustrating that this one did not do so.
So I ended up with the ‘mechanism deck’ and the main board separated out which allowed me to get to the source of the problem.
In all the excitement it seems that I did not get pictures of the crucial part of the mechanism, which lies under the large metal plate in the picture. You can see the floppy ribbon cables and hopefully appreciate how delicate they are.
The diagram in the service manual is quite helpful though:
It was apparent on getting a look at it that the belt ‘FR-A’ was extremely loose, and in fact had a very obvious flat spot on it where it had sat probably for 20 years. This flat spot accounted for the strange ‘pulsing’ effect I was getting. It was a simple matter to replace it with a suitable modern equivalent.
I had a good look at belt FR-B but it appeared springy and in good condition. Replacing it was a bit more involved, with the counter mechanism needing to be removed. I had a good look at this and did in fact remove everything but I didn’t have quite the right belt, and in any case it looked good.
So it was now simply a matter of putting it all back together again – as above this led to some nasty moments, but eventually I had it all together and on testing was pleased to find the fast winding in both directions worked smoothly.
So overall I’m very pleased with this item and with the result. I’d love to get it on a wow and flutter meter but I don’t have one (or the right tape) but there are apparently some ways of doing it on the computer that I’ll need to have a look at. Still I’m very happy to have a rare bit of Sony history to look after.
I was at the ‘Retro Tech UK’ fair recently (which I would highly recommend) and on my third time round the room my eye was caught by what appeared to another variant on the ‘slimline’ design but was a little more expensive than the usual few pounds, and also had some odd looking controls. The seller immediately sprang into action, and told me that it was the “very unusual” Sony TCS-2000. I had never heard of this before, but he explained that the capstan (ie the thin metal rod which is used to drive the roller which feeds the tape through) was driven directly by the motor (rather than connected by the usual rubber belt – an universal point of failure in old devices) and that as a result it had lots of clever tricks.
First of all it mean that the tape transport was extremely accurate and reliable with the minimum of the dreaded ‘wow and flutter’ (being variations in speed which often result from slack or slipping drive belts). Secondly though it made some very special functions possible – such as running the tape at four times its normal speed, reading the high speed audio in and through digital processing playing it back at normal speed in 8s chunks. This means that you can scan through a tape much more quickly than usual but yet listen to snatches of audio played at normal speed helping you to work out where you are in the recording. You can also record index marks as you record and can skip between these again with high accuracy. The seller told me that the main market for these had been ‘the security services’ where they had been used to record interviews, and sure enough it came in a sinister-looking black vinyl case. That clinched it… although as I told the seller “you had me at ‘very unusual’”.
When I got it home, I did look around on the Internet but could find very little about it. There is one article on ‘Walkman Review’ which gives a good (if rather brief) summary of it, but beyond that – nothing. I did find the service manual, and a couple of mentions in catalogues from the time but little else and sadly nothing to corroborate the ‘security services’ story although it does sound plausible. What was interesting was that no other portable Sony cassette – not even the famous WM-D6 range – used this direct drive approach and this must make it one of the most technically advanced and accurate portable cassette players ever made.
I was very impressed by the sheer quality of the build. The controls are largely mechanical (rather than the ‘full logic’ electronic controls more commonly seen on high-end gear) but the keys are brushed metal and feel extremely solid. There are lots of interest looking buttons and switches on it, and very unusually for a unit like this it has two built in microphones providing for a stereo recording. One irritating – and important – thing is that like a lot of modern slimline units (but unlike the ‘classic’ ones from the 80s and before) it does not have a built in power supply and so you need to use either batteries or a 6V supply via a barrel connector. This is a ‘centre negative’ polarity – for some odd reason, as most are ‘centre positive’. I have found some audio gear (including synths, effects units etc) which have the same polarity. So if you don’t have the original Sony power supply (which unfortunately I don’t) then you have to be careful as most power supplies with this connector are wired the other way around.
So with it powered up properly, I was pleased to find everything working. I couldn’t resist hooking it up to my Spectrum and loading a few tapes and as expected the signal was rock solid and the games loaded perfectly. So whilst playback worked perfectly I did notice that on fast forward or rewind the tape wasn’t winding smoothly, and instead was moving in bursts suggestive of a worn or slipping belt. The motor for the winding mechanism is separate from the drive motor, which is again one of the unique features as usually it is the same motor for all functions.
So the next thing to do was strip it down and look for the problem… but this article is long enough so the story continues in Part 2.
Over the last year or so I have really got into cassette players. It started with my interest in 8 bit computers many of which needed a domestic cassette player to get started. The fancier ones (eg the BBC Micro, Atari 400 / 800 etc) had officially branded (and no doubt very expensive) units but the more affordable ones (like my first computer, the Sinclair Spectrum) did not. For this and other reasons there was a huge market for low cost ‘compact cassette’ players, quite different from that for the enthusiasts ‘high fidelity deck’ designs. There is a whole separate history about the rise of the ‘compact cassette’ itself which has been extensively covered elsewhere so I won’t go into that here.
What is evident is that there was also a clear interest in self-contained units with a microphone and loudspeaker built in which were reasonably portable and could be run from batteries (in many ways the fore-runner of the ‘Walkman’). I’ve not really done enough research on this yet, and so I’m not sure quite when it started but the form factor which emerged was a small rectangular unit, similar in width to the cassette with the speaker above and a series of mechanical controls below. These often were referred to as ‘slimline’ designs.
I began picking these up for a few pounds here or there initially because I wanted something to for loading cassette games into my Spectrum, but after a while I became fascinated by the sheer range and variety of these devices, and their longevity. The earliest one I have found dates I think from the late 1960s and is a Philips model. I actually have 2 of these, bought on successive weeks from different sellers for the local car boot. On a recent visit to the official Philips museum in Eindhoven I was very pleased to see an identical (although much cleaner!) model.
They were certainly still popular in the mid to late 1980s fuelled no doubt by the home computer boom and possibly beyond that. I’ve lost count of exactly how many I have – probably 20 or so – and every one is different. Some are clearly bargain basement designs (such as those sold by Dixons in the 80s) whereas others are heavyweight and clearly serious pieces of kit with multiple controls, or else ‘ruggedised’ with bomb-proof thick plastic cases which were probably for educational purposes. I have some others too of different designs including the hifi style decks, and whilst I do like those too I think the slimline units are actually more interesting, more varied but yet much less regarded or documented.
As I’ve written about before I am interested in old technology, primarily computers from the 8-bit era but also other things more generally. Lately I’ve rekindled an interest in old audio gear as well, particularly cassette recorders but also other things too. Cassettes seem to have experienced something of a renaissance lately, not on the scale of vinyl of course but definitely more than previously. I grew up with cassettes, never owning a record player (well not really… I did have a 1960s ‘picnic basket’ one for a while which I bought for 10p at a jumble sale) and relied on them well into the CD era for music on the move. So I do have a real affection for them.
I’ve always enjoyed car boot sales and I’ve been going to these more lately as well, and I’ve managed to pick up a whole range of interesting stuff, most of it in various stages of disrepair. What has been interested is how little documentation there is on this stuff out there – you can often find service manuals, but rarely anything else.
So I’m going to use the blog to document what I’m finding, what I’ve needed to do to bring it back to life and any lessons learned, and also what I think about them. Given the level of interest in retro these days, there is still a huge amount preservation to be done and I’m hoping to play a small part in doing that. I’ve not been very active on the blog lately but I have a lot of stuff to talk about so let’s begin!
With the new battery in place it was time to test the main peripherals – being the cassette and the printer. The cassette drive is actually a plug in module – it could be replaced with a ROM cartridge, and as originally shipped with a simple blanking plate. The quality of the engineering is superb – it feels very solidly made and slots into place with a very positive action. I have a cassette supplied which contains the original logging program for the data logger complete with instructions.
As described above, the tape transport is entirely under computer control including winding, and there is even a digital tape counter accessible from BASIC. The ‘WIND’ command rewinds the tape, and I was pleased to find that sure enough it rewound to the beginning. The ‘LOAD’ command (as expected!) searches the tape for something to load so I typed ‘LOAD’… and nothing happened. No sign of life from the drive at all, and the computer reported a ‘IO error’.
It is very common for old cassette machines to have problems with their drivebelts as the rubber stiffens and perishes over time. However the belt was likely intact to some extent because the winding mechanism seemed to work. It clearly did need the drive stripping down and servicing, and this proved to be quite a task.
Looking round the ‘net it is possible to find some information on how to do this. Given the small scale it is unsurprisingly quite a fiddly job. I’ll make a list of useful HX-20 sites but I’d start with this excellent resource from Martin Hepperle, and specifically the ‘Tips and Tricks for the HX-20‘ PDF:
There’s loads of useful stuff in here, including some advice on replacing the drive belt. There is also a huge stack of other manuals – including a massively detailed technical reference manual – here:
The technical manual gives a very nice exploded diagram of the tape drive, and in conjunction with Martin’s guide tells you everything you need to know. However it is extremely fiddly. The drive itself is a modular unit which slides out (and I understand it originally shipped as an optional extra). There are a few screws to remove the outer shell, and then several more which hold the PCB to the back of the drive mechanism. Some of them have brass standoffs, and all of them are really small so great care is needed not to lose any.
One of the hardest things to do is separate the mechanism from the top shell – it’s not clear how to do it, and takes a lot of wiggling around with the door open to do it. The technical manual talks about removing the front of the tape door but I couldn’t see how to do it and after a lot of fiddling around it eventually came off. So I can’t really offer any advice other than to persevere!
One thing I did learn – do not under any circumstances remove the screw which forms part of the door release latch assembly. I did this thinking it would make things easier, and in doing so the tiny spring which reset the eject switch popped out. I spent a very long time trying to get it back in again… which was incredibly difficult to do. After countless unsuccessful attempts I was eventually able to do it although the spring ended up rather buckled in the attempt.
Once you have the mechanism out you need to unsolder a few wires from the motor, remove the tachometer cap and then finally you can unfold the mechanism and reveal the belt. I had got so absorbed in the process that I didn’t take many photos unfortunately but there are details in the guide linked to above.
To get the belt out, you have to remove another metal bar which sits across the mechanism. The one on mine was intact but had clearly hardened up and was very slack and clearly would not do a good job. However it did not explain why the drive was not working at all, as even a missing belt should still allow the mechanism and motor to start. The belt itself is 50mm in diameter (so about 160mm circumference) with a square cross section. I have a bag of belts of varying sizes so tried a few until I found one which fitted. They do need to be thin enough to pass underneath the tachometer cap so a bit of experimentation may be needed. The cross section should be anything between 0.8mm and 1.2mm square – mine was 1mm.
I then roughly reassembled the module and slotted it back in to see what else was wrong. It was clearly obvious that the real problem was that the tape head was not engaging, and so the computer was behaving as if no tape were loaded. The mechanism is circled on this picture, although here it is in the engaged position.
This mechanism is driven by a separate motor with a worm drive which moves the head in an out of position in a continuous loop. A sensor detects when it is in place which stops the motor. On initial inspection I could not see anything wrong. With long nose pliers I could turn the motor shaft and the mechanism worked smoothly. So the problem either lay with the motor itself or the logic driving it. To test this further I desoldered the wires from the motor (circled on the picture below) and used an external battery pack to see if I could get any life out it:
Initially it appeared completely dead, which was not good news. However, after a bit of fiddling around and without seemingly having done anything, it suddenly burst into life! I spent quite a few minutes watching the motor run smoothly and engaging and disengaging… quite hypnotic. I’m still not quite sure what made the difference, but I think the most likely thing is that the motor had seized through lack of use and a combination of moving the shaft manually and the external power source was enough to kick it into life.
It was then simply a matter of further testing. I reassembled the unit without the case, took a deep breath and…
Success!
It was then a matter of reassembling properly and testing with an actual tape. My unit was was used with a data logger and came with the logging program on tape. It’s not been touched for many years, but I put the tape in typed the ‘LOAD’ command and to my great satisfaction it found and loaded the program:
The final piece of the puzzle was the printer. It was clearly working although the ribbon in it had completely disintegrated. Amazingly you can still buy brand new replacements as a similar mechanism is still used in some cash registers:
You can easily find these – either originals or cheap knock-offs – online very cheaply. On installing it, I was pleased to find that the printer did work but I had a lot of trouble with it apparently jamming. The paper would advance very slowly with constant beeping from the computer. This turned out to be simply due to the plastic gears binding due to a lack of lubrication, and a quick spray with a silicone lubricant (designed for plumbing, but great also for plastic gearing) left everything working smoothly. You can ‘screen dump’ direct to the printer or output to it in BASIC.
The quality is surprisingly good, and I have a box full of original branded Epson paper rolls although these also are widely available.
So after quite an interesting journey I now have a fully working HX-20. There is plenty of other stuff to explore – although the HX-20 scene is quite limited, it is still possible to find software from various sources which can be loaded through an external tape port. I would also really like to see what the data logger can do, will have to think up a suitable retro project for it. Also need to clean up the case a bit. It remains one of a very small group of computers which have printer, display and storage in a single unit. In fact the only other one I can think of is the much later Canon NoteJet / BubbleNote series of laptops
This whole thing has given me a taste for these quirky early portable computers, and I know I would have absolutely loved something like this back in the 80s. Watch this space for more adventures…
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…
I’ve recently got hold of a very interesting retro-tech bundle. I browse the auctions (both traditional and on ebay) from time to time and picked up this bundle. It ticks all the boxes for me – interesting item, with lots of original accessories and manuals, and a bit of a project into the bargain:
If you haven’t recognised it by now, this is an Epson HX-20 which is generally regarded as “the world’s first laptop” and which dates back to around 1980. It is quite a famous machine (although not particularly rare) and there’s a lot of information out there about it. However what’s interesting is that although it clearly was groundbreaking, a few shortcomings (notably the small screen) and the fact that it was probably slightly ahead of its time meant that outside some specialist applications (more later) it didn’t really ultimately succeed as a general purpose computer. The TRS-100 / Tandy 102 ended up as the clear winner in this regard.
I’ve got a lot of time for the Tandy machines and I did actually have one for a period many years ago. However what I really liked about the HX-20 was the clear quality of the design and build and also the fact that it has all the key aspects of a 1980s computer – screen, keyboard, storage and printer – in one very small and integrated package. There are also some very neat touches, such as the micro-cassette drive which is controlled entirely by the CPU.
The one I have came complete with the original carrying case, manuals, two boxes of printer rolls and various other documentation. It also came with a data logger also in its case with all the original documents, even the original invoice. I’ve got some more work to do to research it’s origin but it looks like it was used for something to do with testing and monitoring industrial heating systems. I’ll cover this aspect in another post. I’ll also continue the story in a separate post to keep things manageable. So without further ado…
Universal Discovery Methodology 