Before we begin I want to make it clear this is a guide only. The repair worked for me and I cannot be held responsible for any damage caused to your board or yourself. If you are not a qualified engineer I would recommend this job is left to a professional!
I have a pair of Hypex SMPS400 power supplies that were dead as described in my previous post. When I got them working again I found that both UCD400HG amplifier boards had a hiss and crackle sound when no input was fed into them. When sound was fed into them they would cut out and take a few minutes for them to reset and work again. The fact that both had the same fault might be an indication that this is a common fault so I hope this helps you! Again there was no info online so I checked the obvious first and managed to repair them both.
These are the capacitors that I replaced shown in the following photos.
C40, C41, C42 & C43 they are all 22uF 63v
After replacing all 4 capacitors they powered up with no noise and worked as normal. I hope this helps you to repair your faulty amp module!