What does it mean when the display on a IM / IMA4406 shows IU ?

The IM4406 and the IMA4406 both have the feature that NuTone called "Remote Music Control"  This feature is built-in to the Master Stations and is accessed through the remote stations "End Call" button.

In a properly working system, when the End Call Button is pushed down and held for 4 seconds the radio on the Master Station will turn on and tune to the last radio station that was played.  

Each time the End Call Button is pushed once quickly, the radio will advance to the next preset radio station that was programmed into the memory of the tuner.  If no radio presets have been programmed, the remote advance feature will not work.

If the End Call Button is pushed down and held for 8 seconds, the CD player will be activated (there will be a beep heard on the speakers) and the CD will begin to play the beginning of the CD.

The track on the CD can be advanced by quickly pushing the End Call Button.  If the CD player is in Random Play Mode, the tracks will change in a random order.

Finally, when you are done with either the radio or the CD player, push and hold the End Call Button until the radio or CD turns off.

Each time someone pushes and holds the End Call Button, the display on the Master Station will show "IU".  "IU" stands for "In Use" and this allows everyone to know that the system us being activated by someone in the home.

Beyond the normal and proper operation of the Remote Music Control feature, there are reasons and problems that will make the display will show "IU".

There are 3 fairly common problems that can cause random and repeated "IU" displaying.

1.  If you have a shorted cable or wire between the Master Station and a remote station, the system can act as if someone is pushing the End Call button.  It is also possible that a remote station that has become damaged by water (Patio Station) can have the same effect as a short wire. Entry Door stations cannot cause a "IU" problem.

If a shorted cable or wire or a damaged speaker is suspected, it will be necessary to disconnect each cable from the Terminal Board (behind the Master Station) until the problem is cleared.  A quick method of determining if it is a wiring or remote station problem is to "unplug" the 5 cables that connect the IM4406 or IMA4406 to the terminal board.

2.  Both the IM4406 and IMA4406 have microprocessors that control the functions of the master station, including the Remote Music feature.  The microprocessor uses Logic IC's to carry out its instructions.  Sometimes the Logic IC's will fail and cause the the following variation of the "IU" problem:

The IM4406 or IMA4406 will endlessly cycle "ON - AM Radio - OFF"  This will happen over and over.

These logic IC's are available and are somewhat easy to replace once the problem is identified correctly.

3.  The third cause for the "IU" problem is obscure and difficult to diagnose.  The display will show "IU" constantly and no sound will be heard from the Master Station or the Remote Stations.  The radio tuner can be turned on and off and in some cases the tuner will scan for radio stations, but it will never stop at any stations.

Sometimes the tuner will scan and stop but no radio station will be heard.  Sometime while the tuner is scanning, there will be a loud static sound from the speakers.

If this all seems very random, it is because it is.

This variation of the "IU" problem is actually caused by an IC in the Tuner Control Circuit.  There is a single IC that controls the tuner's scanning and memory functions.  If this IC fails it can cause the "IU" problem along with other erratic problems.

I have also seen Master Stations where this IC has failed and it causes the primary voltage regulator to become burning hot.

This is the original IC used in the IM4406 and possibly some of the early IMA4406 Master Stations

This is the revised IC used in the IMA4406 Master Stations.  This is a very small surface mounted component that has been soldered to a "daughter" board that is designed to fit onto the circuit board where the original IC was mounted.

There are 2 different versions of the IC used in the Tuner Control Circuit and they are not interchangeable.  The later versions seems to be more problematic than the original version.  

If your IM4406 or IMA4406 has an "IU" problem, contact us for help with the problem.

Use this link to contact us about Repairing your NuTone IM4406 or IMA4406 Master Station

Update on Tuesday, November 25, 2014 at 2:23PM by Cindy & Christopher

The Fourth Source of an "IU" Failure in Models IM4406 and IMA4406

The source of the 4th most common failure of a "IU" Problem with NuTone Models IM4406 and IMA4406 is the very common Power Supply Failure, if this failure is left unrepaired for a long period of time (1 year or longer).

Here is a short Video showing how a IMA4406 acts when it has reached this level of failure, and how well it works after the Master Station has been repaired.

As with all models of NuTone Intercoms, the IM4406 and IMA4406 continue to age and the list of "common problems" changes and grows.

As you can see in the picture above, there are a few more components that need replacing to insure proper operation in the long term.  The new additions are not only the intercom relays but the transistors that drive the relays.  

I think that relay failures are mainly caused by systems that are grossly out of adjustment for long periods of time.  This causes excessive wear to the contact points in the relays, which cause them to make intermittent contact when they operate.

Use this link to contact us about the problems with your IM / IMA4406

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