TDA1541 DAC problem (bought off here)

I bought the TDA1541 board advertised here.

Within the first month or so, I noticed that sometimes it was reluctant to lock on to the signal (coax or optical).

Now, the lock LED is on with no signal. As soon as there is a signal, the LED goes off but there is no sound (because it isn't locking obviously!).

Could anybody give me any pointers on what to look for?

The chipset used is TDA1315H+SAA7220+TDA1541.

I have emailed the original vendor of the board 'bbp' but all I got was a reply wanting to know which chipset, and then that was the last I heard.

Can anyone help please?

A link to the documentation (but no schematics) can be found here.