Fading digits after few second of powering the clock

The circuit is not public, as far as I know. My first thought would be to replace the capacitor that is marked 10uF 400V with another 100V one - I don't think the exact value is that important. Anything from 1uF to 10uF should be fine, as long as the voltage rating is > 200V.

Second thought would be to change the small capacitor that is attached to pin 3 of the 34063 - I can't tell you the value, but it is usually 330pF to 470pF.

It's all not very clear on these Chinese boards - I'm not even convinced that they have standards themselves: each board looks a bit different. :-/