Quote:
Originally Posted by Techman
I've got this same model and I have to confess that I hadn't noticed that the transformer had a thermal fuse fitted until it was mentioned here and I looked again at the circuit. As far as I know this model isn't known for cooking its mains transformer, so the fact that it has gives a strong indication that something else has gone seriously wrong in the set to cause it to go. So perhaps I'm stating the obvious by suggesting that the fault within the set that caused it to blow in the first place ought to be found before even thinking about fitting a replacement transformer.
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There are two versions of this and many other models of Murphy radios. Namely, the Welwyn (UK version) and the Dublin (Irish version). Back in time, the Irish government imposed tariff barriers on the importation of UK manufactured goods into Ireland and offered financial incentives for inward investment. Murphy considered it worthwhile to set up a factory in Ireland. ('Anglo-Irish Trade Wars', outside the scope of the forum).
It seems a reasonable assumption that Dick's radio is an Irish made one.
There are various differences between UK and Irish versions of the same models of Murphy radios, perhaps to meet differing regulations, and the use of temperature fuses appears to be one such difference. The fuse is resettable with a soldering iron but requires special low temperature solder. There is sufficient solder for it to be re-set several times (I clean solder free iron and no flux should be used).
The whole idea of the temperature fuse is of course to safeguard the transformer should an overload arise and the temperature rise above a certain temperature. That's what makes me sceptical as to whether Dick has assumed that if the primary is showing open circuit, it's burnt out. Unless I've missed it, I've seen no indication as to whether or not Dick's tested the temperature fuse.
As you rightly say, the correct diagnostic procedure would be to investigate possible fault conditions which might have caused an overload.
Pic 1: Part circuit of the A186 showing the temperature fuse.
Pic 2: Information on resetting the temperature fuse.