Optional second repair. To fully automate the temperature control throughout the seasons, an STC1000 temperature controller was added. (This should only be attempted by those with electrical knowledge, so only a brief outline is given here).

With mains power disconnected, all wires are cut from the control board and extended, ideally with the same size and colour of wire, though holes drilled in the top of the fridge's work-surface (wood/plastic). If you don't want to drill any holes, use longer extension wires and route them through the slot in the back where the mains cable enters.

The mains live is connected to screw terminal 1 and extended to 7 (see circuit diagram in image). The mains neutral is connected to 2 to complete power to the unit. The black wire connects to 8 to complete a switched-live to the pump relay. There is no heater present, so no connections to 5 and 6.

The thermistor wires are connected to 3 and 4. I could have used the thermistor that came with the STC1000, but to save drilling a hole into the fridge chamber, I used one already in the fridge as it appeared to have a very similar resistance (eg 24kohm at 7C). Note: this fridge has two thermistors (see below).

Note: one thermistor is inside and one outside the fridge chamber (I think). If the fridge is colder than room temperature, choose the thermistor with the higher resistance. If the fridge is warmer than room temperature by use of a hair drier, choose the thermistor with the lower resistance.

There are 4 setup adjustments (F1-F4) that can be made to the STC1000, hold button S for 3 secs. F1 is the required temp ( -50C to 100C, default 10C). F2 difference between turn on and turn off (0.3C to 10C default 0.5C). F3 is compressor protection delay time (1 to 10 mins, default 3mins). F4 Thermistor calibration adjustment (+- 10C default 0C).

The temp was set to 7C. The calibration, determined using a separate digital room thermometer, was set in my case to -2C. Other functions used the above default values. More detailed instructions for the stc1000 controller can be found online.

With the above values, (winter room temperature 16C) the compressor turned on for about 5 mins every 35mins and displayed temperature cycling between about 3C and 8C ie a mean of about 5C. Note: the automatic fridge light and off/on switch still work, though the lights and switches on the original control board do not work of course.