Weird Temperature problem

Hi,

I would try and find someone with an inductance or shorted turn checker. It may be a problem with one of the windings. At the cooler temperature the copper will be tighter and you may get a shorted turn. If the core is cracked this would show up too.

A final thought with toroids that is often overlooked. When you switch off a toroid the core, being a ferrite ring, retains the magnetisation at the point of supply cut. If the supply was cut at the maximum positive voltage and then restored at the maximum negative voltage then the supply has to completely reverse the core magnetisation. This causes a very high current pulse for just the one 1/2 cycle. If you don't have time lag fuses then these can easily blow. If you have this problem then it will be a sort of 1 in 10 chance whereas the other candidates will be more consistent.

It does sound like a new transformer will be on order :-(

David





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