PYE Fenman 1 Quiz.

[AndrewLincs]

Hi Alan.

I replaced the mains cable as the (already replaced) white cable had been clipped down to a couple of inches.

I changed 'that' cap a week or so ago and the wax was not in the bottom of the case then. I used the radio a few times but maybe only for half hour or so and it was fine, but last time it had been running for a couple of hours when I heard the popping and crackling, so turned it off quick. I did try it again briefly some time later and all seemed well.

So I'm pretty convinced the transformer is getting too hot, and its interesting that you commented that they do pop and crackle when hot. What would cause the overheating?

Regards

Andrew

[DODGERN]

Hi Andrew,

Overheating of the mains transformer could be caused by a shorted turn in the copper windings.
Have you checked to see if there are any voltage adjustment links on the Primary (input) side of the transformer? Some sets have a voltage selector which may have been set to a lower mains voltage e.g. 210V.

Kind regards,
Roger.

[AndrewLincs]

Some sets have a voltage selector which may have been set to a lower mains voltage e.g. 210V.

Hi Roger

There is a voltage selector on the back of the chassis which allows for two positions 200-225 and 225-250.. the second is selected.

I have just checked an earlier photo and the wax was not present on the wires under the transformer, so I think overheating is the issue. Just need to work out why!

Regards

Andrew

[DODGERN]

At least that's something out the way then.
I think the first things to check would be the capacitors for leakage (not physical) especially the main smoothing caps. If you have already done this you could try disconnecting the output wires from the transformers Secondary windings. If the transformer still ran hot then it would probably mean a replacement transformer. Looks like a busy weekend Andrew.

Regards,
Roger.

[AndrewLincs]

OK, spent some time trying to get my gead round this .. I assume the smoothing cap is the large can on the top of the chassis labelled 32-32 mf C67-68 on the trader sheet... I will search for the method to test this.

So if that tests ok I should remove all load from the secondary side? So remove bulbs, unplug valves and remove remaining wires?

So if it still gets hot when its doing nothing its knackered?

Regards

Andrew

[DODGERN]

Hi Andrew,

I haven't the circuit but what you describe looks to be the correct capacitor(s).
Before you disconnect the wires from the Secondary side of the transformer, you could first try un-plugging the valves. If the transformer still ran hot, you could probably eliminate them from being at fault.
By disconnecting the Secondary side of the transformer, you are removing the load from it, without any load it should run cool. If it's still running hot then you are correct, it's time to go looking for a replacement.

Regards,
Roger.