oscillo PCS 500 velleman
 

i have a oscillo PCS 500 from velleman. Nice thing when you are doing general electrronic.

But since 1 month, i have a problem. channel 1 is not giving anymore correct values.
First, it was saying that calibration fail. and It is true because when you look in the calibration log, there are some parameters failed.
But when you are doing re-calibration. sometimes, it continues to say "FAIL", but sometimes, it is "SUCCESS". But even with this message, channel 1 is not giving good values.

I wrote to them. Yes, of course, i can send to them and pay expensive things. But it is just SMD board with some standard 8-pins components.
Some help please.

Some schematics may be very useful

Thanks
Gunther