Fritzbox 7530 (ZEN) simultaneous use of FON & DECT ?

I am attempting to assist a pensioner friend with a telephony issue that we have run into with his Zen supplied Fritzbox 7530 which is used with a FTTP internet connection. The firmware on the device has recently been updated to the latest (at time of writing) of v7.56. His VOIP telephone line is hosted by Andrews & Arnold (AAISP) and his existing home (analogue) wiring is connected directly to the FON socket on the reverse of the Fritzbox router. He has three hardwired traditional telephones thereupon.

Scenario thus

Device has been working seamlessly for 18 months.

On Friday last

Device updated to v7.56

I introduced a DECT phone into the system

(I know making two changes in retrospect was not a good idea!)

I configured the DECT to use the same AAISP line configured for the FON and upon testing everything appeared to work seamlessly. However over the weekend (for incoming calls) his analogue phones ceased to ring (although the DECT does). Outbound calls are unaffected - dial tone on all phones. Somewhat bizarrely (to my mind) you can dial out via the FON connected analogue phone (and successfully connect to an external number) whilst an incoming call is simultaneously ringing the DECT phone.

I have tried disabling the DECT functionality on the Fritzbox (as in reverting back to the scenario pre Friday) followed by a reboot of the same but the end result is upon dialling his land line the inbound caller hears an engaged tone. I have personally confirmed that all analogue phones are properly seated (and have a dial tone).

As far as I can tell reviewing the AAISP logs the calls in/out are being registered correctly on their system so I presume that the issue is local to the Fritzbox. I am yet to approach Fritzbox for assistance, although I suspect they may just suggest resetting the device to default, which will be a right ball ache to reconfigure (bespoke subnet et al configured)

I am scratching my head somewhat and would welcome any suggestions from my fellow "forumnites".

Is anyone aware whether there are there any logs exposed via a console connection to the 7530 that may be unavailable via the GUI?

In particular can anyone confirm that they are successfully simultaneously using the FON and DECT functionality of the 7530

Unfortunately (at least for now) I do not have remote access to his router, so its a 8 mile round trip to test.

Thanks

In reply to a post by farrinaf:

I am yet to approach Fritzbox for assistance, although I suspect they may just suggest resetting the device to default, which will be a right ball ache to reconfigure (bespoke subnet et al configured)

Does the Fritzbox not have the option to backup the existing configuration? You then do a factory reset and reload the configuration from the saved file.

Thank you for the suggestion - yes it does indeed.

Answering my own question I can now confirm that the 7530 does allow simultaneous use of FON & DECT devices.

As to my underlying problem (now resolved) the issue was that sometime during the firmware/DECT update the FON1 registration (see Telephony/Telephony Devices) representing the analogue telephones connected via the rear port disappeared. Adding it back immediately resolved the issue.

Somewhat bizarre that not withstanding its absence outbound calls from the wired handsets were possible …