NuTone IM406 and IMA406 Music Intercom Systems

IMA406 . . . a superb six-wire, centralized, 20-station home communication system

Master control of Remotes: total 'hands-free” answering

The IMA406's power and sensitivity provide radio reception and intercom transmission of exceptional quality.

As as six-wire centralized system, the IMA406 offers extra flexibility and convenience features. One is “Intercom Only”. This enables you to shut off music to selected stations such as the baby's room, study area, TV room, while retaining intercom capability. Intercom calls can be transmitted to and answered from these “quiet” stations . . . or calls can be originated there.

Another important feature of the IMA406 system is that calls originating at any station. . . Remotes as well as Master. . . can be answered “hands-free”. The person called doesn't have to touch a button to reply.

Whenever you use the intercom, the music is automatically silenced.

To increase the pleasure and convenience of your IMA406, the Master Station has two auxiliary input jacks. You can add both the optional NuTone Fold-Away Record Changer and Cassette Tape Player.

The IM406 represented a leap forward in the design of NuTone's 6-wire Radio Intercom Systems.

The IM406 replaced the Model 2540 and with it's improved control over remote stations, modern AM FM Tuner design and the all new “hands-free” reply, it sets the course for all up coming models. This new platform would only be used until the end of the IMA406's production in 1985, but the spirit of the design would be used in all 6-wire systems until the end of production of the IMA4406.

The original IM406 featured a new amplifier design with dual output transistors. This design was replaced when the IMA406 was released in 1977. The IMA406 had a new amplifier design which used a single Integrated Circuit IC for the amplifier.

The AM FM Tuner was all new in 1975 and a single circuit board module was used for both radio bands. The AM and FM shared a single tuning condenser and used modern IC's for the tuning stages for increased sensitivity. The tuner also had a built-in “squelch” adjustment which allowed the installer to adjust out the static between radio stations.

The newest feature of the IM406 was the 'hands-free' reply feature. This feature allowed just a single person to control the direction of the intercom conversation. Every station included both 'Inside/Patio' Talk & Listen and 'Door' Talk & Listen controls.

This allowed a single person to call out to anyone in the home by using the 'talk' button and the hear the reply by using the 'listen' button. When the Intercom was being used, the radio would be automatically muted, so the people speaking wouldn't have to talk over the music.

All of these features were controlled by the 'Talk/Listen Control Module' along with the muting circuit which is on the amplifier board.

The IM406 and IMA406 were available in 2 versions: The 'L' model was finished in 'Golden Elm' and the 'D' model was a 'Walnut' finish.

There was a huge selection of inside remote stations, including:

IS45 / ISA45: 5” Inside Station finished in Eggshell White with wood-grain look around the controls

IS48 / ISA48: 8” Inside Station available in Walnut or Eggshell White.

IS46 / ISA46: Portable 5” Speaker finished in Black and Wood-Grain

IS47 / ISA47: Built-in Alarm Clock Radio Intercom Station

There were also a variety of inside wall remote controls that were designed to be used with separate wall or ceiling mounted speakers.

Outdoor Patio Stations were either the 5” IS49 / ISA49 which is a surface-mounted station or you could use an IC41 / ICA41 inside wall remote control, mounted in an IA9 outdoor weather shield and connected to a IS79 wall mounted 8” built-in speaker or an ISA77 8” Surfaced-Mounted Patio Speaker.

The choices for remote stations and extra options seemed endless, and this was truly the high point offerings within the NuTone Intercom product line. With a little imagination, a truly great system could be created.

Along with an optional Record Changer or Cassette Player, you could add a NuTone Door Chime to your installation. Just like in the past, the door chime was a separate product that would operate on its own, but also tie into the Intercom System

NuTone still offered the basic 2-note mechanical door chimes, like the LB76, but offered a newer line of Electronic “Musical Chimes”

The new LB55 was a fully electronic chime which included 24 pre-programmed songs. The LB55 had a built-in speaker, which allowed it to be heard wherever it was mounted, but it also could be connected to the IM406 / IMA406 which meant it would be heard through the Intercom System (as long as it was left turned on).

The 10 Most Common Problems with IM406 and IMA406 Intercom System

Lets start off with a question: Why do models like the IM406 or IMA406 last so long before they need to be repaired?

The answer is fairly simple, but not to obvious.  They're turned off alot of the time.

Every NuTone Intercom made before 1982 had a true On/Off Switch.  When you turn the Master Station off, it was truly off - no part of the system was on at all.

A very common occurrence in homes is that things get turned off at night when everyone is getting ready for bed.  You check the locks, you turn off lights and you turn off the Intercom.  NuTone actually would have preferred that you left the intercom turned on, just in case you needed to use it or you have an unexpected late night visitor at the front door, but usually it would have been turned off.

What turning the system off does is increase how long it will last before it needs to be repaired.

It's not at all uncommon for an IMA406 to be sent to us for its very first repair 35 years after it was originally installed.  What a great deal that is!

The number one problem with the IM406 or IMA406 is age. Unlike many other NuTone Master Stations which seem to have their own individual circuits that fail more quickly than the rest of the Master Station, the IM406 and IMA406 tend to gradually and slowly fail as a whole over time.

This long slow slide into failure means that most of these Master Stations are simply 'old and tired'.

You could categorize the design of the IM406 and IMA406 as a 'low-stress' design. Unlike early designs, none of the circuitry is over-taxed or over-worked; it just simply hums along, year after year.

This type of design is very rewarding to refurbish because the final outcome is usually very good.

While all of this is very good, there are a few trouble spots with the IM406 and IMA406.

A complete IMA406 Chassis removed from the face plate 

Problem #1: Intercom Control Switches

The Intercom Control Switches used in the IM/IMA406 and its remote stations are probably the biggest problem with these systems (after aging masters). The switches get dirty very easily and the dirt causes oxidation on the switch contacts.

The oxidation can be removed by using a proper cleaner (DeOxit D5) but surface wear is another issue. In some cases, an injection of a dielectric jelly can quiet noisy switches, but not always.

In severe cases, the switches have internal 'short circuits' which cause the intercom to squeal or have a high pitch whine when you use it. These are often difficult problems to solve because the switch assemblies are no longer available.

 

Problem #2: Master Station On/Off Switch

The on/off switch for the master station is attached to the master volume control (no, it can't be separated from it) and the on/off switch can fail internally, so the system is unable to be turned on or off.

Since the volume/switch assembly is no longer available, the only solution for this problem is a donor assembly from another master station. Fortunately the assembly was used on both the IM/IMA406 as well the IM/IMA303, so there are plenty of used parts around.

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