Simple switching power supply repair help please

[T3sl4co1l]

Your clue is that it can't maintain aux supply.  Some part of the aux supply is broken.

Tim

[Powerspring]

The LD7751 arrived from aliexpress. I swapped it in and ran the PSU with lamp in series with mains.

Success! PSU working well. Output voltages within 10%.

Unfortunately the hi-fi has one dodgy speaker driver but at least the unit works and I've learnt a lot in the process.

Thank you for your help!