The 10 most common problems with a NuTone IM / IMA4406 Music Intercom System

NuTone introduced the IM4406 in 1996 and it replaced the very popular IMA4006. By 1996 everyone was ready for a new top-of-the-line model and NuTone hit a home run with the IM4406.

The IM4406 included a powerful 20 watt amplifier along with AM & FM radio, and for the first time, a single disc CD player was built into the master station. The IM4406 featured “hands-free-reply” intercom operation and remote music control from every station. Probably the only complaint I heard about the IM4406 was the additional cost over the IMA4006.

One concern was the size of the IM4406 because it was 1-1/2” taller than the IMA4006. NuTone learned back in the 1970's that homeowners don't like large master stations, but the additional size was necessary to accommodate the CD player.

There are 3 different variations of the 4406, however the models are labeled as if there were only 2 variations. The original IM4406 was produced from 1996 through about 2002, then the IMA4406 was put into production.

There are actually 2 variations of the IMA4406 and it seems that sometime around 2005 the electronics were updated without the benefit of model number change. This “3rd” model may have corresponded with the change of which factory manufactured the masters.

First I will focus on the original IM4406:

The IM4406 was and has been, a fairly trouble-free model since its introduction. There were the typical new model issues which were mainly CD related problems. Many of these “problems” were associated with the CD player getting contaminated with dirt and sheet rock dust during the construction of a new home. There was also some confusion with the types of CD's that the IM4406 could play.

The IM4406 could play all commercially purchased CD's without any problems, but if you remember back in those days people were just starting to “burn” CD's on their computers and the IM4406 had problems reading these homemade CD's. There was also a rumor that the IM4406 could play MP3 files that were burned on homemade CD's, which was not true.

Unfortunately, the CD player assembly for the original IM4406 is no longer available and there doesn't seem to be any reasonable repair option for the original player. The original CD player assembly was manufactured for NuTone by a vendor which made CD player assemblies for many different companies. As with all modern manufacturing, once the demand for the assemblies is gone, the vendor stops production of the units.

There are basically 2 problems that occur with the CD player:

1. The motor that moves the lens (which reads the CD) will fail and the lens just stays in one spot. While this is a small part, it is not possible to purchase replacements from the original vendor.

2. All CD players will eventually develop a problem with the laser that reads the information off the CD. The laser beam will become weaker and weaker over time and finally it will become so weak that the reflection off the CD is not strong enough to be read. Again, without an exact replacement from the original vendor, repairing this problem is not possible.

(The original IM4406 CD Player Assembly)

Since the use of CD's has diminished a lot since 1996, the best and most popular solution with our customers is to abandon the CD all together and add a miniature input jack to the side or bottom of the IM4406. This jack can be used for any MP3 player (iPod or iPad) or an external CD player. This jack can also be used to connect a satellite radio receiver (XM or Sirius).

Power Supply Failures: 

A new problem that seems to be developing with the original IM4406 is the failure of the power supply circuit on the Power / Amplifier circuit board. This should not be confused with the 2 low-voltage transformers (model 801T's) that are mounted in the IR105 Wall Housing. (Caution: The 801T transformers have built-in internal fuses, if the output of the transformers is shorted, it will blow the fuse and the transformer will go dead. The fuse is not replaceable and a new transformer will need to be purchased!!!)

The first sign of trouble with a failing power supply on most NuTone Intercom Systems is an increase in the background noise of the system. All NuTone Intercom systems had a certain amount of background noise which could be heard if you listened very carefully with your ear up against the speaker. This light “hissing” sound is called “white noise” and it's the sound an amplifier makes when it's turned on.

This background noise was eliminated with the introduction of a new intercom platform in 1994. All of the NuTone models produced from 1994 through 2008 were designed with a “stand-by” mode. When the intercom system was not in use (not listening to music or using the intercom) the amplifier will switch off and the system became silent, no more background noise.

Since the IM4406 has a “stand-by” mode, when the power supply begins to fail, a homeowner will not hear the increase of the background noise of the system. It's not that the increase isn't there, it's just that since the system is in “stand-by” you can't hear it.

The first symptom a homeowner may notice is a random “static” or “crackling” noise from the speakers even when the system is in stand-by. There may also be a loss of volume with the music and door chime. Most of the calls we receive are when the IM4406 is at the point of failure and nothing is really working except the clock.

 (Pink arrows point to voltage regulators)

The power supply in the IM4406 is a modern design and it uses components to create many different electrical voltages, which are used to power different parts of the IM4406 master station.

(Aluminum Heat Sink for the Power Module)

 

Most of these power regulators are mounted to the massive aluminum heat sink on the back of the power module. However there is one regulator that is not mounted this way; it is just mounted flat against the circuit board.

(voltage regulator removed, dark area on circuit board caused by excessive heat) 

Over time, and while the values of other supporting components drift, this regulator will start to run hot. Over time it will continue to get hotter and hotter, and since the regulator is not mounted on the heat sink, the excessive heat it generates has no place to go and the regulator fails.

I have seen units where the regulator could be pulled off the circuit board with your fingers because the solder connections had failed due to the long term exposure of the heat. When this regulator fails, the IM4406 stops working.

Luckily, repairing this problem is very straight forward, but for a long lasting repair more than just a new regulator will be needed. All of the supporting components in the power supply circuit should be changed and the primary capacitors should be checked and replaced as needed.

There is also a modification that should be done to improve how the regulator is mounted in the power module. This modification is based on a change that was made in the final version of the IMA4406.

 

An aluminum bracket needs to be fabricated and the regulator needs to be mounted to one end of the bracket. The other end of the bracket is fastened to the metal covering of the large aluminum heat sink. This gives the heat that the regulator generates a path to the large heat sink. This modification keeps the regulator operating temperature well within the normal range for this component.

 

These types of voltage regulators are available with different power output ratings, for different applications. We use a replacement regulator which has a higher rating than the original component and it also has a different case style, which works better to transfer the heat away from the component.

The original regulator has an all plastic case and the replacement has a case with a metal backing plate to aid in the transfer of the heat. Since the metal backing plate is conductive, it is necessary to use a insulating transistor mounting kit when attaching the regulator to the bracket. Without this kit the regulator will fail quickly.

Along with the regulator replacement and bracket modification, there are 6 capacitors and 4 diodes that will also need to be replaced.

 

The power supply circuit for the IM4406 includes 7 larger capacitors. These have not been a big problem on too many IM4406 Master Stations, however there have been a few units in which these capacitors have failed. It's a good idea to check these capacitors with an ESR meter and evaluate their condition. If they show any signs of increased resistance, they should be replaced.

 

When the repair of the IM4406 is completed, the power supply circuit should last longer than the original design. The IM4406 may be the high point of NuTone Music Intercom System design and it certainly is worth keeping it in good working condition.

See all of the IM4406 pictures here.

Ask a Question.

Make a Service Request.

Update on Wednesday, March 13, 2013 at 2:49PM by Cindy & Christopher

A Toasty IMA4406 was delivered to the shop today!

I know that I've already done an IMA4406 power supply rebuild article but I really think this IMA4406 will be an interesting repair.

This IMA4406 came from a customer in New York with the following description of the problem:

"This IMA4406 is 7-8 years old and within the last 2-3 months it has begun to work erratically and now it continually show "IU" on the display."

I was very surprised when I opened the box and found the plastic heat sink cover to be so discolored.  I have repaired lots of IMA4406's and I have never seen anything like this.

You can easily see how discolored the plastic is compared to a normal looking IMA4406.  I don't think the discoloration is from where the master is installed because the plastic cover over the CD player is still clear.  It seems to me that this unit must have been very hot for a very long time to end up like this.

The area around the voltage regulator is discolored and the regulator is somewhat loose on the board.

Tomorrow this unit will be on the repair bench, I can't wait to see what it's really like when its powered up.

More to come. . .

Thursday, March 14th

I put this toasty IMA4406 on the bench today and nothing looks good at this point.  The power supply / amplifier module is toasted and the master is cycling on/off, on/off,  on/off while the display just shows "IU"

I temporarily replaced the power supply module with a known good module and I swapped out the main control board with another good board and the constant "IU" problem on the display and the cycling went away, but there is no radio from the speaker in the master and the Intercom operations are all wrong.

I also noticed that the LCD display was lit unevenly, with some segments dark and other segments look much lighter and the seem to flicker.  As I stripped the IMA4406 down, removing each board and inspecting them, I found one set of resistors in the display circuit are discolored from heat.

I got the go ahead from the customer to do more diagnostic work on this master.

More Tomorrow. . .  

Wednesday April 17th

This IMA4406 is finally complete.  It had so many problems that it was necessary to install substitute circuit boards to help narrow down the problems board by board.

The Power Supply Module was the simplest part of the repair and I actually rebuilt it last, after making sure that all of the other problems could be solved.  A new voltage regulator mounted to a new heat sink bracket and some new capacitors and diodes put the power supply back into good working order.

The Main Control Board had the most problems.  While the customer did not report any power surge or lightening issue at his home, I suspect that one of those situation caused some of the damage I found.

There were logic problems with the intercom control circuits; there were two failed voltage regulators on the board, the op-amps for the chime inputs produced a distorted sound and the AM/FM tuner and some of the supporting integrated circuits had failed.

This is a lot of damage to have on just one board.  A symptom of these problems was the massive overheating of the power supply module.  I used a temporary power supply module while I was working on the control board.  The power supply would heat up very quickly, so hot that the components could not be touched.  This was caused by the failed circuits on the main board drawing to much current and over taxing the power supply.

Once the main board was repaired, the overheating power supply problem went away.

The Processor Board had just a few problems, there were some over stressed resistors for the LCD display and a few logic IC's that needed to be replaced.

The CD player did not function after the rest of the IMA4406 was repaired.  This may not be related to all of the other problems.  The CD players in IMA4406's have always be a troublesome and it is likely that it failed at an earlier date.

The last issue was with the plastic faceplate itself.  After being exposed to a great deal of heat for a long period of time, the plastic has become very brittle.  There are many small screws that attach the circuit boards to the back of the faceplate and these screws thread into standoffs on the faceplate.

These standoffs are now so brittle that the screws just shatter the plastic when they are installed.  I used some hot glue inside the screw holes and around some of the boards to help reinforce everything and hold it together.

In the end, this was a successful repair, oddly enough about a week after this was delivered to us I had another IMA4406 show up in almost exactly the same condition.  It leads me to believe that if a failed IMA4406 is left unrepaired for a long period of time (or a short time with a dramatic failure) it will be more severely damaged than average.

Update on Tuesday, January 7, 2014 at 7:25AM by Cindy & Christopher

Here are just a few pictures of an IM4406 with a more extensive power supply failure.

You can clearly see the crack in the voltage regulator.  This was likely caused by either the regulator being severally overheated or perhaps that this IM4406 had all of the signs of a failed repair attempt.  One giveaway is all of the Thermal Compound (the white stuff) under the power supply components.  There is easily 10 times the amount of Thermal Compound that is needed.  I also found that the Power Supply Module had been disassembled prior to the Master Station being shipped to us.

Since there were so many unknowns about this IM4406, I decided that a complete Power Supply rebuild was in order.  

The board was depopulated and all of the components were replaced.