I cracked the code on the horns.

I was working on getting @Tirnipgreen's re-plated horns working. I tinkered with them some a while back, but I needed some time to focus on them to get the bugs out.

Fortunately I had one of my old 260Z horns that was unmolested to use as a template.

Before I go into detail, let's talk about the theory of operation.

1. When you press the horn button, the relay sends voltage to the horn.
2. The coil in the horn is energized, pulling the diaphragm in.
3. The bar on the back side of the diaphragm hits a tab on a set of contacts on the negative side of the coil, de-energizing the coil.
4. The diaphragm snaps back into place, allowing the contacts to close.
5. Repeat steps 2 through 4 as long at the horn button is depressed.

The vibration of the diaphragm is what makes the sound.

So what appear to be the potential failure points?

1. The tab for the positive wire on the outside of the horn loses electrical contact with the coil inside the horn.
2. The contacts get carboned up.
3. The bar on the diaphragm is not aligned properly.
4. The tone screw is not adjusted properly.

I don't have a documented fix for #1. You see it by measuring resistance between the outside tab and the inside of the horn where the coil wire is mounted. Ideally, you should have continuity.

For #2, test by measuring resistance from the positive side of the coil to the body of the horn. It should be less than 2 ohms. To lower resistance, I cut a 3/4 inch wide strip of 1000 grit sandpaper and folded it in half. I worked it between the contacts and pulled it through a couple of times, using the tab on the contacts to moderate the pressure. I measured resistance from the positive to body of the horn until it dropped to less than 2 ohms.

For #3, I took a straight edge and held it against the side of the bar. There are two alignment holes on the diaphragm, and I noted the distance between the straight edge and the hole. It's between 1 and 2 mm. If the bar on the horn you're working on doesn't line up that close, loosen the M6 nut and rotate the bar. Hold it in place carefully while locking now the nut.

After adjusting the internals, put the horn back together. Measure resistance from the positive tab to the mounting bracket of the horn. If it's more than 20 Ohms, the tone screw is turned in too much. The tone screw is an M4 screw on the back of the horn. The screw in the photo below was powder coated onto the horn, and I had to break it loose. I got the resistance from being over 1 MOhm to around 2 ohms.

After that I used a car battery to test the horn and get a better tone. I had to work the screw in and out a few times until I was happy with the results.  

 The other horn was a little more challenging. When I tried to break the screw loose, the screwdriver chewed up the head. I had to replace it with the only screws I had available, allen head screws.

After playing around with the height of the screw, I finally got a decent volume out of it.

 

 

 

So last night I wanted to see if I could improve the sound from the horns @Tirnipgreen asked me to work on. One was nice and strong. I wasn't going to mess with success. The other wasn't working, though it worked before. I could tell it was pulling in the diaphragm, but the contacts weren't opening. This was verified by taking current measurements on that horn and one that worked. The non-working horn was pulling a lot more current. I tweaked on the parts repeatedly, but I couldn't figure out why that one horn would not work.

Finally out of frustration, I took the other horn apart to compare the diaphragms. The problem then stuck out like a sore thumb. Whoever reassembled the diaphragm on the horns didn't put the parts back together in the right order on the non-working horn. The fiber washer was on the wrong side of the bar between the diaphragm and the bar. This is how is should be.

So when the diaphragm tried to open the contacts, it was still providing a path to ground for the coil. With the coil still energized, the diaphragm wasn't moving. Once the diaphragm was assembled properly, the horn worked just fine.

With the new knowledge, I decided to re-shoot the video to go over the details of the horn. I just have to edit the new video.

I am the responsible party and stand in shame. OK...now let's drive...!!!

59 minutes ago, Tirnipgreen said:

I am the responsible party and stand in shame. OK...now let's drive...!!!

I actually consider it a fortunate mistake because it gave me a better understanding of how the horns work.

Loving this thread!!!!

It’s inspired me to re-start the work on my horn.

2 hours ago, AK260 said:

Loving this thread!!!!

It’s inspired me to re-start the work on my horn.

Well, if I have enough time today, I'll finish editing and post the video.

Good stuff! I haven't had a horn since 2017.  I've been yelling like a crazy person out the window in lieu of a working horn.  

A working horn isn't going to stop the yelling. Not for me anyway.

46 minutes ago, Reptoid Overlords said:

Good stuff! I haven't had a horn since 2017.  I've been yelling like a crazy person out the window in lieu of a working horn.  

So, to get this back on track, here is the video I was promising.

 

Steve, I've done the continuity test, 1.6 ohms between the positive tab and the far side of the contact.

The only thing I haven't done is install the thin paper gaskets.

 

So, to get this back on track, here is the video I was promising.
 

LOVE this video!! Nicely done sir!