Light aircraft intercom problems

[pipertommy]

Hi, hopefully this is the correct place to post this issue.
The issue is with a friends aircraft, cessna 172. Rear passengers can only hear but not be heard on the aircrafts intercom system. The comms are working fine in the front.
The aircraft has a single plug setup with the split lead for two plug GA headset adaptation plug into each single socket.
Wondered if any technical experts could shed some light as to why the rear are only receiving but not communicating?
Appreciate any assistance you can provide.
Thanks.

[NutLoose]

How old is the Aircraft, some radio set ups have the facility on the main coms panel to disable the rear seat mikes when talking to ATC etc to stop ATC getting pax chatter.

you will see it as an example on here

top left 0.13secs in selector for pilot / crew / all.

https://www.youtube.com/watch?v=HtWAebf0JkQ

[pipertommy]

It's 1960's, old panel. New addition of a 8.33 radio.

[NutLoose]

any idea the make?

[pipertommy]

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1080x1920/screenshot_20190630_082437_17c2261902b2421d265de119d020ec83b 765c1fc.jpg
This is the panel with the 8.33 icom newly filled.

[NutLoose]

Does it have a separate intercom?

manual for the radio btw

http://www.icom.co.jp/world/support/download/manual/pdf/IC-A220_IM_ENG_2.pdf

[pipertommy]

Separate intercom? Sorry, naive with this kind of stuff. Lol

[NutLoose]

Yes.......... does it have something like an SPA400 fitted?

https://www.aircraftspruce.com/catalog/avpages/spa-400.php

[pipertommy]

It does have one of those fitted