I spotted this on the BVWS stall at the NVCF, its an MTV1B which is the UK version of the second series Microvision. It looked a bit sad, with dried-on sticky tape marks and holes drilled in the cabinet, but I’ve not seen one for ages so I thought I’d give it a go. This model was introduced in 1978 and at the time was the smallest TV set you could buy in the UK. It runs from four ‘AA’ sized cells and has a 2” electrostatically deflected picture tube. It was really quite an achievement; remember the first Sony Watchman was still five years at this stage.
At home I tried the set and it didn’t work. Thinking about that, I stripped the cabinet away and sprayed it in label remover. After that a long soak in hot soapy water removed the worst of the tape marks. I filled the holes in the cabinet by first covering them with electrical tape on the outside and then back filling them from the inside with epoxy resin (rapid type). Heating this gently with a hair dryer while it cures makes it less viscous, so it runs better into the features of the void it has to fill. Once the resin was hard, the tape was removed and the surface touched in with black paint. Its not perfect, but it looks pretty good.
Back to the tiny chassis. Applying 6V across the battery snap showed no current drain so I checked the switch – open circuit. Shorting it out made the screen light up instantly (the tube is directly heated) so I scraped the contacts clean and tried again, this time it worked. There were a few issues to attend to to deal with the effects of battery leakage in the past and a bit of suspect soldering, but after that a picture could be tuned in. There was also sound but it wasn’t very good.
If you are used to normal sets then the Microvision can be a bit baffling. A lot of it is built on three purpose designed ICs – they are not replaceable so if you damage one you can’t repair the set. A fourth IC does the intercarrier sound, that is a standard part from Hitachi. The tuner is also special, it uses a negative tuning voltage for its variactor diodes and is largely hand made – something else to be careful with. The electrostatically deflected tube means that there are high voltages everywhere, sometimes where you’ve least expect. The line and frame shift controls for example have a cool 2kV on them, and any flashovers are likely to ruin the ICs. Some of the holes I filled allowed access to these controls, so the set wasn’t really safe like it was.
I found a circuit diagram for the set but it was a different issue to mine and differed in some details. The scan was also hard to read, but it gave the general idea. The various preset controls are not marked and with such a strange set it seemed a good idea to work out what each one does and see which was not having the desired effect. A combination of clues on the diagram and in the set allowed me to work it all out, looking from the front and working back the functions are:
Right Hand Side (under the tube):
front: height
front middle: focus*
rear middle: frame shift*
rear: line shift*
Centre:
front: width
middle: set -45V
rear: contrast
Left Hand Side (behind the tuning control)
front: preset line hold
front middle: user line hold
rear middle: user frame hold
rear: AGC
Controls marked * are at a high potential and must only be adjusted with a non-metallic insulated tool – I used a ceramic screwdriver.
I started with the set -45V control. With exactly 6V at the battery snap I set this for -45V on the wiper of the control itself, the diagram shows that this is tied to the -45V rail. I did it with the set tuned in to show a normal picture and the sound muted.
The AGC should be set to give a ‘clean’ picture from a strong signal (modulator output loosely coupled to the rod antenna etc). Some settings will give line pulling at the top of the picture so look carefully. The contrast control (internal preset, there is no user contrast control) also does some odd things so needs to be adjusted carefully. Because of the short length of the tube the focus is a compromise setting but it should be possible to get it pretty good – I could easily read the programme guide from the Freeview receiver with it set up optimally. The is no brightness control so with everything else about right the picture will still look a bit bright and grey – that just seems to be the way these sets are.
After all that the results looked pretty good. With the sound at a moderate level the current consumption is about 120mA with a battery end voltage of about 1V per cell. This suggests that good battery life is possible if alkaline cells are used. The tuning does drift as the battery voltage falls however, part of the circuit economy is that the tuning voltage isn’t accurately stabilised.
There are a few things left to do. Firstly, the little screw terminals for an external antenna are missing, as is the spring contact inside for the rod antenna. Can anyone who has one of these sets photograph these parts for me so that I can make new ones? Also, the stickers underneath are missing – again if you have one of these sets could you scan the bottom in for me (it would come out best it if the flexible prop stand was first removed).
I have the first Watchman too (FD-210BE), this came from the NVCF years ago and had a duff converter transformer which I rewound. See:
www.walkmancentral.com/products/fd-210be
It gives a brighter and more contrasty picture than the Sinclair but the latter is still an impressive piece of work, especially given the era in which it was designed and the tight budgets that were available to do it.