Vintage Synth Repair

Hi
I just dusted off my TX816 only to find that turning the power on does nothing. No glowing LEDS anywhere.
It was working when I put it away.

The AC seems to pass through the filter OK so I assume it is the switch mode power supply (dated 1986).
Nothing burnt and no visibly leaking caps. There is a 470u 200V electro cap (C7 for those with cct diagrams) with a slightly bulging top.

I must confess mucking about in the 240V realm is a bit daunting.
What is the best approach to fixing this?
What are the most likely failure modes in a switch mode supply?
Can I leave the power supply disconnected from the other boards to test it or does it need to be loaded to function correctly?

Thanks

Royce