Shunt Reg… need help

This is a simple mono shunt reg using TL431 as the shunt control over a transistor.
It works as is but when I join grounds from each rail I have a short and can’t figure out the reason.
Attached is the layout of component over the PCB and a picture of the real thing.
Can someone point which is the problem?
Thanks, Tony


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I think the problem is that you have CT transformer, so you have to connect transformer CT tab to ground as well, or just split transformers secondaries if you can. Moreover, if your inductors are common mode type, you can make CLC filter after each diode bridges, but if they are differential type, wire them as a LC filter in each power supply line only, they are not needed in ground rail.
The problem is that you are using two bridge rectifiers; this would be fine if it was not a center tapped transformer but two isolated windings. With two bridge rectifiers your power supply grounds are not isolated from each other. If you use one bridge rectifier and the transformer center tap as ground you will be fine.