Halogen transformer again

This doesn't make much sense to me, how can half the bulbs connected to a single transformer go off? Unless, of course, the bulbs themselves have failed or have become disconnected.

I'd carefully check all the existing wiring and the bulbs before going to the trouble and expense of replacing the transformer. It seems quite likely to me that you simply have some loose wires.

If you do decide to replace the transformer you need the 150 watt one,

Is there the remotest possibility that the present transformer has more than one secondary winding (or output, if it is not an actual transformer), one of which is faulty?

Chris

I've seen older low voltage transformers configured to have two sets of output terminals each protected by a (replaceable) fuse. Only one secondary winding, though. TLC used to sell them. Other possibility is a fused output junction box.