When the frig light fails, you generally start by replacing the lamp.
When this doesn’t fix the problem, its time to read the manual.
The Coolmatic manual doesn’t have a circuit diagram, or any reference to a fuse.
Next contact the factory for advice. They confirmed that there is no fuses in the frig, and suggested that the lampholder may be faulty.
Troubleshooting
Removed the lampholder & switch assembly and checked them both to be OK.
There was no voltage at the lampholder, which gave two possibilities,
1) the lamp is fed from the thermostat switch (faulty? Hey the frig still works OK)
2) the ground wire is broken?
Chasing wires was first option using the access panel at the rear of the frig (not easy).
Found three wires connected together by two small capacitors, clamped to a small aluminium channel (heat sink). This was fitted with a 7812 semiconductor voltage regulator that had its leads broken off.
This wiring supplies power to the frig lamp. The reason the voltage regulator is necessary is because the Coolmatic can run off 12 or 24 volts.
The frig lamp is 12v, & 24volts would kill it.
Reason for failure.
The small heatsink has a cable restraint fitted to it to hold the three wires feeding the 7812. However there was a large loop of wires (150mm or so) from the clamp to the terminals of the 7812. These wires are soldered to the 7812, and any vibration movement on a soldered connection from wires of this length is a guarantee of failure. (We have travelled several thousand km of corrugations).
The fix
Simple replacement of the 7812 purchased from Jaycar Electronics @ $1.20.
I also extended the heatsink by about 30mm and repositioned the cable clamp at the end of this extension. This means that the cable is fixed between the soldered connections and the cable clamp. This prevents movement and possible future failures.
This is a bit long-winded, but I hope this simple fix may save someone the future frustration of finding a fix to a simple problem of a lamp not working
Neil
