Dublo A3 Power Control Unit not working

[ray_liffen]

it's a Dublo Power Control Unit that is not working. Type A3 (with forward and reverse). The 'power on' light does not light. With the cover off, the transformer seems to be getting 240v but there is no AC going to the rectifier. is this a known fault? Open-circuit winding on the tranformer?

A circuit diagram would be helpful. Is 'reverse' simply a DC negative voltage fed to the track?

[96RAF]

You work inside a mains powered device at your own risk. Officially it should be worked on, then tested and certified by a qualified person.

[Yelrow]

Ray, Methinks its time to replace. Look for a H&M Duette or clipper on ebay, if you want same sort of power. Not something one should play about with, in my view.

[P-Henny]

This link may help. But looking at the photograph of the internals, I would relegate this controller to the bin and replace it with something more modern.

https://dublonutz.blogspot.com/2016/07/inside-a3-controller.html?m=1

P.S. The A3 in the link also had an open circuit transformer coil. This suggests that this type of transformer winding fault may possibly be fairly common with this unit design.

[ColinB]

It sounds like you know what you are doing and if you say there is no AC going to the rectifier then it sounds like the secondary of the transformer has a fault. These old transformers tend to have a variable resistor wound round an asbestos core, for that reason I would leave well alone. I have in the past removed all the old internals and replaced them with modern equivalents but that is probably going to cost more than buying another one.

[ray_liffen]

Thanks for your replies. The dublonutz website item is useful. I think I shall get (or make) a low voltage power supply and feed it to the (isolated) DC tags of the rectifier in the A3. That way it will replicate the transformer/rectifier combination. My two-rail hornby layout has all the utility buses - points, lights, signals etc, fed from an 18v 1.5A Power supply that I built using a 7818 voltage regulator. Cricklewood Electronics, here I come! The only problem I forsee is that if positive and negative voltages are needed, a transformer with a centre-tapped secondary will be needed.