| How To | 08/27/2010 |
Nutone IM5000 Chime Doorbell Intercom Repair
| How To | 08/27/2010 |
I installed a Nutone IM5000 intercom in our new house in 2006. Is has worked great, with the exception of the doorbell chime module.
Every time lightning strikes near by, the chime module gets destroyed. So, I have taken the time to learn how to repair it. I thought I would share it with others, since I can find no documentation on the internet about the IM5000.
Also, below I will show how to install a couple of tranzorbs and caps to reduce the number of times the IM5000 chime doorbell is damaged by lightning.
Part Locations
You must replace all of the parts at the same time, or the replaced parts will be damaged! |
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What goes wrong
The NPN transistor Q401 controls the coil of the DSY2Y relay, using a TTL signal from the CPU. This transistor may test good, but it needs to be replace. If the audio amp turns on, and the relay is not energized, the audio amp will be destroyed, since its output will be connected to ground.
The Diode D405 is across the DSY2Y relay coil to protect the transistor Q401 when the relay coils energy is released. This diode shorts out from the lightning spike. Replace it!
The DSY2Y relay toggles the speaker wires, to the doorbell speaker, between the microphone preamp and the 2 Watt audio amp. The relay does not normally burn out. If the contacts are ohmed out, it will look like the N.O. & N.C. contacts are shorted, but they are not. The output of IC403 is shorted to ground, and the input to IC404 is shorted to 12VDC. The false short is actually just the switching power supply.
The Resistor R401 couples the two signals(Pre-Amp & Audio Amp). It is the only "give" between the pre-amp(IC404) and audio amp(IC403). If the DSY2Y relay does not energize, and the audio amp IC403 turns on, R401 will glow red, then burn open. Replace all the parts before applying power!
You can see in the picture that I have modified R401 from the original configuration. I have replaced the 1/8 Watt 10 ohm resistor at R401 with a 10 ohm 2 Watt resistor and a 0.4amp resettable poly switch connected in series. This way I didn't have to keep replacing R401 while tracking down all the problems on the PCB.
The Op-Amp IC404 amplifies the audio signal from the doorbell speaker when the intercom is in "DOOR" mode, and the "TALK" button is not pressed. Strangely enough, when hit by lightning, the input to this op-amp shorts to the power rail, which is 12VDC.
The Audio Amp IC403 amplifies the "TALK" audio signal when in "DOOR" mode, so you can hear audio on the doorbell speaker. When hit by lightning, the output of IC403 shorts to ground.
The Diode D402 is supposed to protect from reverse voltage on the speaker? Piss poor design to use a 1N4148 signal diode for protection. This shorts out, or burns open when hit by lightning. It will look shorted if you do not remove the speaker wires and the DSY2Y relay. Just replace it.
The Diode D413 is supposed to protect from reverse voltage on the Nutone door chime audio module PCB 62900 or 62901? Again, piss poor design to use a 1N4148 signal diode for protection. This shorts out, or burns open when hit by lightning. It will look shorted even if it is good, since it is across the switching power supply.
The Diode D412 clamps the audio signal to the op-amp IC404. This gets shorted when hit by lightning.
Replacement Part Numbers
D402, D405, D412, D413- Original part # 1N4148. Replacement Part # NTE519. Signal diode. At only one point in the circuit does it appear to be used correctly?
Q401- Original part # 2SC3198. Replacement Part # NTE85. Description - NPN transistor to energize DSY2Y relay.
IC403- Original part # TBA820M. Replacement Part # NTE1294. Description - Op-amp for audio input from the doorbell speaker when the "DOOR" function is activated, and the "TALK" button is NOT pressed.
IC404- Original part # TL082CP. Replacement Part # NTE858M. Description - 2 Watt audio amp for audio output to the doorbell speaker when the "DOOR" function is activated, and the "TALK" button is pressed.
R401- Original part # 1/8 watt 10 ohm resistor. Couples audio in and audio out going to doorbell speaker.
Parts and part dealers can be located at www.nteinc.com
Added Protection Install two P1.5KE15CA's in series, with a 600v 0.47uF cap across them, from the "COMMON" terminal to the input that your doorbell button is connected to.  Install three P1.5KE18CA's. One across the two doorbell speaker terminals, and one from each doorbell speaker terminal to the earth ground terminal. |
has the best price on all auto parts, and their service is great.
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Final Thought - Other than lightning damage, the Nutone IM5000 has been a good intercom.