HP 5110 fax interruption

[Vinitoo]

I have a HP 5110 Officejet All-in-one printer/fax/copier/scanner which is connected to a telephone answer machine.
Once in a while, when I answer a phone call, the fax machine will cut off my call after a few seconds. I hear silence on my end, the caller hears a fax tone.
I have the fax machine set to pick up after 5 rings, the Answer machine after 3 as the HP manual suggests.
I know it isn't the answer machine since I have replaced it and the problem continues.
Also I know the the device(s) are connected properly.
I tried HP support but after a few suggestions with no success they do not have an idea.
Any help would be greatly appreciated as this is a big annoyance.
Thanks in advance.
Vini

 

[Tedster]

I would increase the time for the fax to pick up an incoming call. There should be a modem command in the instruction book.