DIY: Troubleshooting & Rectifying a Car Horn


Thread Starter #1
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Oct 21, 2016
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Pom Pom, Peep Peep.

A familiar sound on the Road. A device given in your car to get attention of the people in surroundings to yield way for you to pass.

The Horn.

Although I detest using it unnecessary in the city runs, it's one very important device on the highways specially on the ghats to intimate oncoming traffic on the blind turns.

Well, most cars have a pair of Horns that sound at a little different pitch. The combined pitches creates a good loud sound enough to tear through the surrounding Noise and make a mark.

But if you listen to the sound of a single horn separately, its too low and ineffective.

Even for a car like Safari with one Horn gone Kaput, The single horn literally feels like that of a Scooty [embarass].

In my recent trip I had to face a similar situation. One of the Horn stopped working and with the Single Horn it was too frustrating and embarrassing to sound the it on the curves.

Somehow completed the trip safely without any issues.

No use of the car for the next 3-4 days and then on Monday had to travel to Pune from Mumbai.

Expressway is good enough to not require a horn.

In the evening thoughts are running about the horn. What to do? Go to the garage and get it checked or try on own.

Lately have been doing a lot of DIY at home as well fixing few electrical/electronic things. The wave is still alive and I decide to give it a try.

Before We move further on what I did to rectify the horn of my car lets have a look at a Videos to understand the working of an Automobile Horn.

https://www.youtube.com/watch?v=rJV2iu3BzmY

So from the Video what we understand is the horn creates the Sound by continuous vibration of the Diaphragm.

For the Diaphragm to Vibrate it is continuous pulled and released by an electromagnet.

The pull by the electromagnet causes the contacts of the circuit to break and disable the magnetic field and release the Diaphragm. This allows the spring loaded contacts to connect again enabling the electromagnet to pull the Diaphragm again repeating the cycle.

This remind me of the Door Bell working we learnt somewhere in Class 5 or 6.

From the above inputs below are the probable reasons that would make the horn stop working.

1. Coil creating the electromagnetic field getting damaged.
2. Connections to the coil from the external leads getting damaged
3. Ruptured Diaphragm
4. Broken Spring loaded contacts
5. Oxidised Spring loaded contacts not allowing the Current to flow through the circuit.
 
Thread Starter #3
Joined
Oct 21, 2016
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Location
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Sorry Guys Could not update in past few days.
Blame some work pressure and More importantly the Lazy me!

So the mission starts with the very first step -
Step 1: Locating where the Horns are placed.
A quick help from the members of the SOUL Whatsapp group and I was able to find them.

Sorry do not have actual pics but the marked area in the below pic is where the horns are place behind the Bumper/Lower Grill.

Safari_Front.jpg



Now how do I access them. Well don't be scared. You do not have to remove the bumper or the lower grill. Removing the Upper Grill is more than enough. That too you need not completely the remove the upper grill out.
For removing the Upper grill you need to undo six screws along the top of the grill along with two 1/4 inch bolts at the two ends. Thanks to TAIger bhvm for this input.
Once these are removed you can just pull the grill ahead to create a gap good enough to insert your hand and access the Horns.

The two horns are placed side by side each supported on the integrated bolt with a Nut at the other end. The reference image from the internet will give the idea.

Roots_Windtone.jpg

The Red marked is the bolt and Nut arrangement. The Blue marked are the leads that are connected to the wiring.
The Yellow Marked is the covering over the Diaphragm in the shape of a megaphone or we can say a Shell which helps amplify the sound by concentrating the sound waves.

For removing the Horn, First Pull out the wires connected to the leads. These will be the simple plug in -plug out type metal plugs.
Unfasten the Nut pointed in the above picture with the help of a Spanner or a Plier and you have the Horn in your hands.

Step 2: TroubleShooting

As I mentioned earlier the probable Causes.
1. Coil creating the electromagnetic field getting damaged.
2. Connections to the coil from the external leads getting damaged
3. Ruptured Diaphragm
4. Broken Spring loaded contacts
5. Oxidised Spring loaded contacts not allowing the Current to flow through the circuit.

So first I checked for the leads that connect to the wiring. They looked perfectly OK. No rust, oxidation or any such thing. Still as a precaution cleaned them with the Magic Potion WD40

Now to check further, the Horn needs to be opened up. This can be done by unfastening the 4 screws you can spot in the above reference Picture.
Once the screws are removed the megaphone or the shell shaped plastic cover comes out. Have a look below.

20181120_175714.jpg


After observing closely, the first 4 reasons were ruled out. Everything looked perfect.
Now the only suspect was the spring loaded contacts.
A closer Look of the Setup.
20181120_175723.jpg


The White marked is the Movable Spring loaded contact.
The yellow marked is the fixed contact stub. The underside of this stub makes contact with the movable contact.

The red line shows the flow of current.

There was no issue with the spring action and it was working perfectly. Both the contact points were touching each other. However oxidation over the period had caused a kind of insulation and hence hampering the flow of current.

To clean the contact I rub them with the tip of a flat screw driver followed by generous amount of Magic Potions WD40 Sprayed on it. Put back all the parts together and fastened the screw just enough to hold them.

Step 3: Testing
Now what I see is there isn't any audio circuit to send a particular sound signal to the Horn to produce the sound. Its just the Current input that is required to oscillate the Diaphragm and produce the sound waves. So for testing you do not really need to connect the Horn back to its wiring. You can just connect the two leads of the horn to the two terminals of the car Battery. Or in case you have a 12V DC source at home, that too is sufficient.

Connected two wires to the Horn Leads. Held 1 wire against the Car Battery Positive terminal.. Then tried by just rubbing the other wire at the negative terminal very briefly for just less than a second.
Note: It is very important to first test with the Brief rubbing as in case there is any short in the coil a longer period of current flow would Damage/Drain the battery.
Voila the Horn sounded.Then again tried, this time by touching the wire to the negative terminal for a couple of seconds to assure it is indeed rectified.

Post this primary testing fastened the screws on the Horn tightly. Then connected the horn leads to the original Wiring. Before Fastening it with the Nut Bolt in place tested with the Horn Switch.
Wow the Sound is Back, From the Scooty to the Beast.

Step 4: Fixing back the Horn and closing the Grill
Well nothing special in this step. Post final testing Fastened the horn with the Nut and Bolt in place.
Set the upper grill in place and fastened the six screws at the top of the grill along with the two Bolts at either ends of Grill.


Well that's the story. Hope this helps fellow TAIgers. Although the explanation is for the Safari DiCOR, the overall troubleshooting steps should be same for other cars as well except for the location and accessibility of the Horn.

Thanks!
 
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