Lightboard   (1975 - 1982)
Strand

One feature of the TCS systems at the National that might be slightly surprising was the way in which the system was required to behave in the event of a major failure that rendered the system inoperable. The required behavior was that, after 10 seconds, all of the channels would fade to blackout.

Now, in practice, the sample and hold circuits which drove the dimmer control lines would almost certainly have been able to hold their existing levels for at least a minute or two without any noticeable drift but, unfortunately, some earlier memory systems (IDM, I believe) had the characteristic of turning everything full on in the event of a failure so this was seen as being a possible failure mode and it was decreed that this was something that "must not happen" at the National.

Actually this requirement that nothing should cause the entire rig to turn on at full was quite reasonable considering what the maximum load in the Olivier was likely to have been - it's just that the way in which this was enforced was, perhaps, just a little too paranoid.

The "fade to blackout" behavior was enforced by separate hardware which drove analog inhibitor circuits 10 seconds after a failure was detected.
The failure would also have have triggered the audible hard warning which, in turn, triggered a Pavlovian response in the operators who immediately dived for the backup master controls. Unfortunately, the backup masters were neatly recessed in the front of the control desk with a cover over them on top of which notepads, pencils and the occasional coffee mug tended to accumulate and getting to them in time required unceremonially sweeping this detritus onto the control room floor.

Fortunately the lighting control rooms were very soundproof so, providing that the thick glass window was in the closed position, the audience would be unaware of the drama that was unfolding behind them but I am told that some of the shows were run with the control window open in which case there would have been very audible "sound effects off" along the lines of: "beep-beep-beep-f**k!-*crash*-f**k!-beep-beep-beep ..." ... until the control room window could be closed.

Another feature of the TCS systems which was quite new at the time was that the control desks could be positioned remotely from the racks that contained the PDP11 computer and the main electronics of the system and, indeed, that was how the installations at both the National Theatre and the Burgtheater in Vienna were done, with the control desks in good location at the back of the auditorium and the racks hidden away in a separate room somewhere backstage.
(The Royal Opera House installation was quite different to say the least and, perhaps the less said about it the better ...)

Anyway, while this separation of control desks and racks made perfect sense for lots of reasons, it also made for a *lot* of walking for a service engineer working on the system.

At the National, the control racks for both the Olivier and the Lyttleton lived in the same room backstage which was very convenient but also introduced a number of potential hazards.

One of those hazards was the fact that weight of the computers and the center of gravity of the racks was such that you could only safely pull one computer out of the racks at a time. If you tried to pull out both of them at once, the racks were in significant danger of tipping over. At some point, I think, someone actually fitted a short chain to the backs of the two computers, the length of the chain being such that you could pull either one, but not both, of the computers out of the rack at the same time.

Another hazard was making sure that you were actually working on the correct system - you might be there one afternoon working on the Olivier system while there was a matinee in the Lyttleton - it was necessary to think carefully before turning anything off...

There was another problem which could easily double the number of times that you needed to walk between the control room and the racks if you were working on your own.
TCS1 systems used a quarter inch cartridge (QIC) tape for both program storage and cue storage. To boot the system you inserted a program tape, turned a keyswitch and pressed a button to select the program that you wanted to load (either "lighting" - the normal TCS program - or "hardware test"). This was all very simple, convenient and straightforward but there were a few issues.

The first issue was that, as initially configured, the systems at the National could only be "cold booted" from the PDP11 front panel. The switches and buttons on the Tape control panel were just scanned by software and only allowed you to reboot the system if it was already running.
In normal use this didn't really matter - the lighting program would be loaded and running and when the system was powered off and powered back on again the system would automatically come back in the same state that it had been in when powered off.
The problem was that,if you were working on the system and it crashed and you needed to reboot it this involved the following steps:

1 - go to control desk
2 - power system on
3 - insert program tape in tape reader
4 - go to computer rack
5 - load the start address of the bootstrap code and run it
6 - go to control desk
7 - remove program tape from tape reader

Now, anyone looking at this will quickly realize that this whole operation could be significantly streamlined if the program tape was just left in the tape drive at all times. Unfortunately this was not generally regarded as a safe option.
The tape drives had a reputation for not powering up cleanly and being prone to corrupt tapes which were in the drive when the system powered up by writing a small amount of garbage data on whatever piece of tape was under the read/write head at the time.
Leaving a tape in the drive when the system was powered down probably wasn't as dangerous, but now you had a tape sitting in a drive on a powered down system which would presumably be powered up again in the near future at which point disaster might strike.

At the Burgtheater I had devised a partial solution to this problem. If I was at the computer rack and needed to cold boot the system I entered a small 3 instruction program which tested one of the buttons on the tape panel and, when it was pressed, jumped to the bootstrap code.
That way I could walk back to the control desk, insert the program tape, and press the button which would then cause the bootstrap to be initiated.

At the National in around 1982 I installed two of the newer "restart boot" cards which were used on later TCS systems and which could initiate a cold boot from the control desk regardless of whether or not the system was actually running.
My recollection is that this was done as a goodwill gesture by Strand - we had a couple of extra cards in stock after the two Stuttgart TSC2 systems has been built and we knew that we were never going to build another TCS so why not just give them to the National...
Installation of the cards was quite challenging because we needed to find a couple of extra wires in the cables that connected the control desks to the computer racks, so that the reboot buttons on the tape panel could be directly connected to the bootstrap card.
In principle this was easy - there were lots of spare wires available - but the real challenge was finding them on a connector that was reasonably accessible without having to dismantle the entire control desk to get at it. Unfortunately, there was no connector that was really convenient so we made the best of the situation and used the one that was least inaccessible - I don't remember all of the details but it definitely involved lying on the floor of the Olivier control room for more than an hour trying to get the necessary wires from where they were to where they needed to be.