Milen,
I am sad to inform you that there is no active development on this product
anymore. You can tinker with the receive sensitivity, and see if it makes
any difference.
S38 controls the receive sensitivity. Its default is 43 which means -43dbm.
You could try going to 44 or 45 and see if that helps at all. As you go
lower (higher numbers), the modem will have trouble distinguishing between
noise and signal and may not drop carrier when it should.
I would recommend up dating to our MT5634ZBA-V92 if you want to use a modem
with active fax development on it.
Steve Tuckner
Multi-Tech Systems