Erratic Operations caused by Failed Relays
Monday, June 3, 2013 at 2:56PM I had an IMA4406 delivered to the shop last week with a list of odd operational problems. The list included:
1. The radio and CD played correctly at the Master Station, but could not be heard from any of the remote stations.
2. The door chime (IA28) could be heard at the Master Station, but nowhere else.
3. The voice intercom could transmit to the door speaker from the Master Station, but the reply could not be heard.
4. The intercom functions could be activated from the remote stations, but no voice transmission or reply could be heard .
5. The remote Radio/CD control feature worked from the remote stations even though no music audio could be heard from the remote stations.
I verified the list of problems and started looking for the source of the problems. All of the problems pointed to a single type of problem, a lack of audio throughout the remote sections of the system.
The IMA4406 does have a fuse on the audio output, incase one of the pairs of audio output wires becomes shorted. This was not the problem.
After checking voltages on the amplifier board which all seemed correct, I started looking for a bad solder joint (I recently had an IM4406 in with about 1000 bad solder joints).
After resoldering many joints I reassembled the IMA4406 to see if I had made any progress; I hadn't.
One technique when looking for cold or cracked solder joints is to flex (carefully) the circuit board in the attempt to make a change (for good or bad) in the operation of the unit. This is done with the unit powered up (so care must be taken).
I noticed that when I pushed down on the board the radio began to play through the remote station on the work bench. Removing the pressure cause the radio sound to disappear. More resoldering was done in the area of the board that corresponded to the pressure technique. This did not solve the problem.
I then noticed that pushing down on one of the 4 relays on the board would cause the music to return, hmmm.
I recalled that back in 1994 and 1995 there were some IM3303's that had problems with similar relays. I have not seen this problems spill over to the IMA4406, but it was worth a try.
I replaced the 4 relays on the board, reassembled the unit and it worked. Problem solved!
The IMA4406 has a micro-controller and logic IC's to manage it's operations but the relays do the heavy lifting when it comes to directing the audio in and out and through the system.
It will be interesting to see if these relays make it onto the 10 Most Common List in the future.
Cindy & Christopher
This past week I have another IM4406 in the shop with an odd problem that was sort of the opposite of the IMA4406 I wrote about with the bad relays.
When the IM4406 arrived, I noticed that someone else had tried to repair the failed power supply, and this attempted repair was not completely successful. Before I started on the power supply, I swapped in my shop power supply/amplifier module. This is a good and quick way to determine if there are any additional problems.
What I found was that the Master Station was silent: no radio, CD, or chime. The tuner appeared to be working correctly so I connected it up to a terminal board with two remote speakers.
I was surprised to find that the radio would play through the remote speakers as did the chime. The intercom functioned correctly between the remote speakers, but not to the Master Station. While checking all of the operations I noticed that the clicking of the relays in the Master didn't sound quite right.
The clicking of the relays was rough sounding, not the normal click and release sound that I'm used to hearing.
I replaced the 4 relays in the Master Station and then everything work correctly. I guess bad relays may become a more common problem in the future.
Cindy & Christopher
Relays in all NuTone IM4406 and IMA4406 have been added to the 10 Most Common Problems List for this Model.
My first post about problems with the relays in the NuTone IM4406 and IMA4406 was back in June 2013.
Since that time I have had many IM4406 and IMA4406 Master Stations in the shop for repair and I've noticed a pattern with the relays. . . they all have a tendency to become unreliable over time. They haven't truly failed, but they do not operate correctly 100% of the time.
I outlined some typical symptoms in the 2 earlier articles, so I won't repeat those issues. What I'm seeing is Master Stations with relays that work intermittently and when they operate, they sound wrong.
So, how do you know what a good relay should sound like? Well, it should make a solid "click" sound when it is activated (I've heard thousands of relays, I know what a good one sounds like). So, what does a bad relay sound like? The best description is that it sounds "crunchy" with sort of a "ratchety" noise (you know it's wrong when you hear it).
It's also not just the relay that typically needs to be replaced, but the transistor that drives it. I've had several Masters that even with new relays didn't operate correctly 100% of the time, until the transistors were replaced.
Replacing relays and the transistors that drive them will be a normal part of repair all IM / IMA4406's