Cub Conversion

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Colour but in black and white

Although YSTV broadcast in Colour from 1986 onwards, many of the monitors in the control room were still black and white, with only a few key output monitors displaying colour. A large ex-broadcast Sony Trinitron and two smaller baby Trinitrons were the only permanent colour tubes (the remainder being Cotron monitors and a handful of other sub 10" diagonal screens).

This, along with the mixed sizes of monitor, made mounting them into the mixed collection of wooden shelving difficult. It also made it hard to know what the on-air picture would look like until it got there, by which time it was often too late.

By the late 1990s the large numbers of BBC microcomputers supplied to schools were being replaced by PCs as technology marched on. Almost all of these had Microvitec "Cub" monitors with them. These were steel-cased 15" monitors, capable of displaying full colour. They ran at the TV picture size and frame rate (625 lines, 50 Hz) since the BBC could also be hooked up to a TV if you didn't have a dedicated monitor, making them ideal for displaying video. They remain prevalent even today, making spare parts abundant at very low cost.

Almost but not quite

The cuboid Cub

The snag was that the model with a composite video input suitable for connection to the studio was almost unheard of, with most purchasers having opted for the basic model with only an RGB input at TTL levels, suitable for connection to a BBC micro but almost nothing else. Indeed a larger 21" chassis had been used for a number of years as the studio monitor, perched high on top of a spare cabinet, which was infact a Cub in disguise.

This problem was solved by the construction of an adaptor board that could be installed into the back of the monitor to perform the decoding of the composite video signal into it's RGB components to be fed into the monitor. The digital RGB input was disconnected and replaced by the analogue RGB from the converter.

A new monitor bank was envisaged for the station using 18 of these monitors (three rows of 6) to display all the important live video signals to the control room. The monitors were relatively cheaply and easily available second hand, so accumulating a set was not a problem, indeed a number were obtained from Hookergate primary school through a contact of Peter Elvidge who lived nearby.


The innards of the upgrade

This circuit was created by Rob Sprowson, and a set of 18 duly created in May 2000, together with a new, steel monitor rack sized so that the monitors would fit neatly on it. The station mains wiring was upgraded so that the wall behind the rack had enough mains sockets to plug everything in directly (see the G/046 page for the tale of how this was done), and YSTV could now see every point of the vision path in colour. The old Cotron black and white monitors were cascaded to become part of the NaffoCue system.

There was even a service guide produced, and the whole project cost around £400, including buying the custom circuit boards.

A minor error on the original converters was later corrected in November 2000 by the insertion of a small buffer board soldered directly on the back of the input connectors. As Rob has graduated by this point their installation was a little rushed and the monitors weren't properly adjusted for good colour balance across all 18 monitors.

Almost all of the Cubs 'whistled' without video being input, and some even when there was a video input, as a free running oscillator in the Cub tended to squeal at a distressing frequency. Fortunately this was trivial to stop, usually by desoldering the linearity coil and putting it back in the other way round, or better still covering it in hot melt glue to damp its resonance.

A later revised buffer board was designed in 2004, and fitted in May 2004 to one selected monitor. It both offered an extended temperature range but also featured an 8 pin microcontroller which would generate a fake black picture should the source video be unplugged - minimising 'whistle' potential.

VGA converters

Although a very good idea, the Cub monitors suffered from a lack of regular maintenance. Their tendancy to get quite hot in continuous use (they have been seen in use as Pizza warmers) meant that some key components aged prematurely but were not replaced, leading to tell tale picture artifacts (too bright, too dark, oversaturated, etc...).

By 2003, this lead to a steady campaign (lead by Rowan de Pomerai) to get the monitor rack upgraded to something that actually showed accurate pictures. After much debate, deliberation and experimentation this was achieved in 2006 by the use of the VGA Converter Boxes, allowing the worst of the cub monitors to be scrapped and the remainder relegated to secondary use on OBs and loans to other people.