occasional bad signal

[PerryM]

I have a 6981 in a Win7/64bit system, using DVBViewer both live and with the Recording Service. It is a dedicated HTPC so spends most of its life 'asleep'. About 1 in 10 times that the 6981 card is used, it shows a bad signal. Not completely gone but very very poor so error rate is unusable. In the live situation I can reboot DVBViewer and get a good signal again. In the Recording Service I have (of course) no such opportunity and lose the recording. I have searched this forum but there is nothing exactly the same - anybody else suffering?
I have recently tried installing the latest driver, changing 'sleep' to 'hibernate', adding a boot delay in the DVBViewer options, and updating the DVBViewer apps. Nothing changes!
Any ideas? I should emphasise that 9/10 times the system is working fine.
Worst case I am willing to buy a new 6982 card - it clearly has a different tuner module but what is the difference in practice?