my custoner has a nutone door box outside and a recieving unit on the inside. powered with a transformer. no model number on it. he says it doesnt work interminently. i told him i would need it to not work at all to try and trouble shoot it. im not familiar with it. he also wants to get a second reciever unit on the door box. anyone have an answer on either one of these things. thanks. dave

Time to pull out the tools. Remove the devices and find the part number(s). Those aren't always obvious to laymen, (such as saying my Nortel system is a M7310).Your profile states you hobby as working on all systems so here is a new challenge for you.

The mechanics are identical with everything electrical that you have worked on previously, so troubleshooting is the same.

You cannot install an additional device without being onsite and find out first hand what you are working with. And then research Nutone Website for the proper devices and possible replacements for legacy equipment.

he decided to go with viking door box and ring his phone on unused port