The normal problem with a fax that will not receive calls it the phone
The Line Voltage, or current may be low, or the signal ( DB loss) may be affecting it.
Let me give you an explaination. When you send, you physically connect to the phone line, make the dial tone and whatever is there, it goes out over the line.
When you receive a fax, it is like a remote control
, with a remote you need good batteries
to generate enough signal to turn on a product.
With a fax, you require an electrical signal, like a remote control to activate the receive capability. Low power, voltage or current. or static, will not allow it to receive, just like a remote with a bad battery
will not turn on a product.
Issues can be. The phone cord between the fax and the jack. A bad jack, something on the outside line.
Using a digital phone
line, or having another device on the same phone line drawing down the line, or picking up. A credit card
machine, answering machine, even another phone can cause issues. If on a shared phone line, disconnect everthing but the fax and have someone send you a test fax. See if that helps.
But more than 90 percent of fax will send , will not receive issues are phone line related.