How to restore Mixo horns

[merbesfield]

Does anyone have any info or links to how to restore Mixo horns? I had hoped these would work sad is, but the high tone wouldn’t sound. Not sure what I’m looking at on the inside. Here are some pcs I took.

[Jones]

There are two coils and a set of points in there, when power and ground is applied through the coils the circuit goes through the points turning the coils into electro magnets. The magnetism pulls the heavy steel plate down, and the pin pushes on the spring loaded points and opens them, killing the magnetic field causing the plate to release, and the points to close again, and the cycle repeats.
You could start by filing the points (if you have points files great, if not, a metal fingernail file would work), then check continuity through the circuit. You could just try holding the plate there and powering it up again to test if the magnets are working.

I'm just working on my banjo horns, same principle, only one coil though.

Good luck.

[merbesfield]

So many questions. Pls keep in mind I’m not an electrical guru. One of the contacts is lose. The small nut on the outside is rusted to the stud and looking on the inside I don’t see a way to hold it down to tighten it. See red circles on images.

On the inside where the stud is there is a tab of sorts. Is this tab supposed to be connected to anything?

The plate on the back cover doesn’t seem to move. Is it supposed to move as you say be able to be pulled down when magnetic field is applied?

Does the stud on the back outside of the cover have anything to do with grounding, or is it strictly a mounting stud?

When you say check continuity, do you mean between the two tabs on the outside?

[72targa]

Just going off of memory, but I recall a thread here where someone put modern electronic units (MBZ?) on the vintage horns. Just a thought…

[gled49]

If the red trumpets are real nice, I buy new horns and swap out trumpets. I’ve also found a perfect plastic paint from Kaylon, safety red if u don’t have red trumpets.

[Jones]

So many questions. Pls keep in mind I’m not an electrical guru. One of the contacts is lose. The small nut on the outside is rusted to the stud and looking on the inside I don’t see a way to hold it down to tighten it. See red circles on images.

On the inside where the stud is there is a tab of sorts. Is this tab supposed to be connected to anything?

The plate on the back cover doesn’t seem to move. Is it supposed to move as you say be able to be pulled down when magnetic field is applied?

Does the stud on the back outside of the cover have anything to do with grounding, or is it strictly a mounting stud?

When you say check continuity, do you mean between the two tabs on the outside?

Hi Mark,

The tab should be connected to the coil circuit somehow. soak the nuts with penetrating fluid, and try holding the stud inside with needle nose pliers and tighten the nut. The heavy rectangular plate that is attached to the thin round disc will cause the plate to flex when the horn coils are energized, acting sort of like a speaker through the trumpet. The tone should be adjustable with the screw on the outside (closest to your fingers in the last picture). The stud on the back is just for mounting. Yes continuity between the two terminals, you could check that with an ohm meter if you have one.

Below is a quick schematic of how the circuit could work, I have never seen inside a Mixo horn, but this should be close. The points complete the circuit, until it is energized and the plate moves to open the contacts. ...sorry about the un-cropped image, I hope it makes sense.

[NorthernThrux]

If the points are clean, the it's the winding on the solenoids that burnt out. That's a bit trickier to fix, though possible if you have patience to rewind them. I found a cheap set of the later black versions on eBay and transferred the innards to my red ones. Works great.

Ravi

[merbesfield]

Good morning guys, you have been very helpful. Electronics is not my forte, but I’m trying to learn and this helps. What I am still unclear on is what does the tab attach to? I don’t see any sign of where it would have been attached. Everything inside looks very clean. No signs of rust of corrosion. Also, should there be a seal between the body halves? There wasn’t one upon disassembly but the mating surfaces were corroded as you can see in the image. Thanks, Mark

[NorthernThrux]

You might find this helpful. https://p-car.com/diy/hornrepair/ . Different 911 model, but the same horns.

And yes, there is a thick paper gasket between the body halves. I see it in your photos. it's just compressed and degenerated (much like one of my spine discs).

Ravi

[merbesfield]

You might find this helpful. https://p-car.com/diy/hornrepair/ . Different 911 model, but the same horns.

And yes, there is a thick paper gasket between the body halves. I see it in your photos. it's just compressed and degenerated (much like one of my spine discs).

Ravi

Ravi, I feel you. My spine is the same. Makes working on cars quite difficult. Feel better.