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testing a horn coil
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 5:21 pm    Post subject: Reply with quote

I have tried to get the coil to pass a current by doing as you suggest but the bulb will not light.

I have tested across the points but nothing is getting through. I get the feeling that the coil is duff.

If the coil has burned out then from what I can see, it is game over. There seems to be no way of removing it without damage as it would appear be a force fit in the case.

I may have to buy a refurbished replacement horn or get mine professionally rebuilt

Either way it is £200. Shocked
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traction39



Joined: 19 May 2009
Posts: 399
Location: South Wales

PostPosted: Thu Sep 24, 2020 5:24 pm    Post subject: Reply with quote

On the 200 ohm setting the meter has a beep symbol. This will beep if the coil is continuous i.e there is no break in the wire / when you connect the two probes together. Check again directly on the coil- a beep will indicate a good circuit...
My penny worth.
Alistair
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Alistair

Citroen Light 15 1953, "12" 1939,
Riley 9 Special 1932
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Thu Sep 24, 2020 5:29 pm    Post subject: Reply with quote

Note the position of the inconspicuous adjusting screw.


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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 5:31 pm    Post subject: Reply with quote

MVPeters wrote:
It's a bit late now, Ray, since you've dismantled the horn, but a couple of times in the past I've re-tuned horns of that type.
I've just cleaned the contacts, connected 12V & gently tweaked the adjusting screw. Slowly turning the screw makes the horn rattle, then beep, then squawk & finally parp the way it should.


Me too but I was told by the p.o that the horn was u/s. and I was intending to fully refurbish it anyway.... but I can't see any way of removing the coil - even if I could get a replacement.

Other than shelling out £200 the only other option would be to force out the coil and make one from varnished copper wire.
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 5:41 pm    Post subject: Reply with quote

traction39 wrote:
On the 200 ohm setting the meter has a beep symbol. This will beep if the coil is continuous i.e there is no break in the wire / when you connect the two probes together. Check again directly on the coil- a beep will indicate a good circuit...
My penny worth.
Alistair


Good point!

Having checked it out I can tell you now there is no "beep" coming from the meter.

It looks like I shall have to buy another multi meter. Rolling Eyes
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Thu Sep 24, 2020 5:43 pm    Post subject: Reply with quote

Might be worth checking the battery in your multimeter.

Peter
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Peter_L



Joined: 10 Apr 2008
Posts: 2680
Location: New Brunswick. Canada.

PostPosted: Thu Sep 24, 2020 5:51 pm    Post subject: Reply with quote

Ray White wrote:

Other than shelling out £200 the only other option would be to force out the coil and make one from varnished copper wire.


Amazon.co.uk. 12V Horns, or your local motor spares store.
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traction39



Joined: 19 May 2009
Posts: 399
Location: South Wales

PostPosted: Thu Sep 24, 2020 5:59 pm    Post subject: Reply with quote

It may be worth checking the continuity of the cables/probes. Plug in one of them and stick the probe end into the other socket. Repeat with the other one! This way you know the cable/ probes are OK assuming the meter is good!
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Alistair

Citroen Light 15 1953, "12" 1939,
Riley 9 Special 1932
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 6:39 pm    Post subject: Reply with quote

peter scott wrote:
Might be worth checking the battery in your multimeter.

Peter


I changed it but just the same.
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 6:47 pm    Post subject: Reply with quote

Peter_L wrote:
Ray White wrote:

Other than shelling out £200 the only other option would be to force out the coil and make one from varnished copper wire.


Amazon.co.uk. 12V Horns, or your local motor spares store.


There are reproduction "Altette" horns available but they are not as well made as the Lucas original. Also, there were so many different Lucas versions,, which reproduction one is supposed to be authentic.?

Also, they don't last long.

( In my humble opinion, the sell out of Lucas was a betrayal of customers and share holders alike.) Sad
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 6:51 pm    Post subject: Reply with quote

traction39 wrote:
It may be worth checking the continuity of the cables/probes. Plug in one of them and stick the probe end into the other socket. Repeat with the other one! This way you know the cable/ probes are OK assuming the meter is good!


Thats a good tip..

Thank you I will try not now..............


The leads are fine. The meter just reads 0.00


Last edited by Ray White on Thu Sep 24, 2020 7:11 pm; edited 1 time in total
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Thu Sep 24, 2020 7:08 pm    Post subject: Reply with quote

I think it is unlikely that the coil winding is open circuit. The wire thickness is quite substantial. Corrosion may be the problem. I would spend more time investigating connection points inside the casing.

Peter
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 8:27 pm    Post subject: Reply with quote

peter scott wrote:
I think it is unlikely that the coil winding is open circuit. The wire thickness is quite substantial. Corrosion may be the problem. I would spend more time investigating connection points inside the casing.

Peter


I must say it would be a great relief to me if I could show that the coil is sound. I also had not expected to find a problem with the winding. I may be wrong but I would have thought if the points stuck shut they would have burned out first??

However, I have checked and cleaned the points and found nothing amiss. I tested across the points but got nothing so perhaps there is a wire broken inside the cloth covering?

I have also made sure the wires are not shorting out on the sides of the body and the connections are good....
Confused

Not withstanding the rusty diaphragm; the parts all looks to be in exceptionally good condition.

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Peter_L



Joined: 10 Apr 2008
Posts: 2680
Location: New Brunswick. Canada.

PostPosted: Thu Sep 24, 2020 8:34 pm    Post subject: Reply with quote

Red Neck "Bush Test". Stick a pin, as in a sewing pin through the insulation of one of the cables and see if you get 100% conductivity back to the soldered connection. Try it on both, if you get 100% across the pins, the problem is at the soldered joint.
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Sep 24, 2020 8:53 pm    Post subject: Reply with quote

Peter_L wrote:
Red Neck "Bush Test". Stick a pin, as in a sewing pin through the insulation of one of the cables and see if you get 100% conductivity back to the soldered connection. Try it on both, if you get 100% across the pins, the problem is at the soldered joint.


I could try it Pete; but those soldered connections.... they look just fine to me.

Another view from a slightly different angle:

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