Tidbits

This is a quick post covering some odd bits and pieces that probably don't warrant a full posting on their own, at least not yet.

Power Supply

As already outlined, the Computox has two relatively simple power supplies.  All the lamps are fed from a pair of 2VAC supplies generated from two taps off a Varley transformer.  Each supply is independently fused, leading to the following schematic:

2VAC amp power supply

All relays and other components are run off a DC supply.  This is believed to be 24V, although this has not been confirmed (according to GPO datasheets the minimum operating voltage of 3000 series relays with 500 ohm and 1000 ohm coils seems to be about 12V).  Interestingly, the DC power supply looks to be unregulated and unsmoothed (no large smoothing capacitors are visible):

24VDC relay power supply

As already noted, the bridge rectifier used is either a selenium or copper oxide unit, and as you can see, it's showing its age.

Computox rectifier

Game Counter

The mechanical counter on the front of machine is simply operated by the RESET button as shown below:

Game counter circuit

When the RESET button is pressed, a circuit is completed that powers the coil of the second unselector, a 22 ohm resistor and the game counter.  At the same time RESET cuts power to the *XA and *OA relay coils, resetting the machine state.

Winner Lamps and Bell

Similarly to the counter, the bell circuit is very simple.

Bell circuit

When either the W or L relay is activated the B2 changeover switch makes a circuit to ground ringing the bell.  This makes the bell closely related to the winner lamp circuit which is activated by the T1 switches on the W and L relays, as shown below.

Winner lamp circuit

"Secret" Switches

There are a pair of micro-switches mounted in the bottom front corner of the case.  These are located below the bell on the left side of the case, and behind the 24V transformer on the right.

"Secret" micro-switch

These switches protrude through the base of the main unit just behind the front feet and are operated from below, as shown on the left of the next image.

"Secret" micro-switch protruding through the base next to the foot

According to other members of the Museum's team these are cheat switches that can be used to reduce the computer opponent's level of play, allowing a human player to win.  Simon states that at demonstrations the Computox's creator enjoyed allowing children to beat the machine, whilst preventing adults from doing so.

It should be noted that the Haufe patent describes a similar feature (column 3, lines 30-40).  This acts on the machine's move selection algorithm, preventing it defending potential forks.  The change in strategy is activated by opening or closing both 385 switches, highlighted in the diagram below. 

Haufe patent "secret" switches

If these switches are open, breaking the link between the uniselector and a number of relays in what the patent calls circuit "h", the optimal response is blocked, allowing the human player to set up a fork.

Like the Haufe machine, the two micro-switches used on the Computox are single poll.  Testing suggests that in the Computox they are wired in parallel with one terminal connected to 24VDC ground and the other connected to one of the switch terminals on the second uniselector (it remains unclear what this uniselector does).  Therefore, the Computox appears to incorporate a similar feature to the Haufe machine, but potentially with a different implementation.  Clearly, some more investigation is required.