Testing coils

[electro-diy]

I'm trying to test some coils for continuity, but I'm not sure I'm doing it right. Below are photos of 2 of them. For both of them I tried to test resistance between the bare wires you can see connected to the tabs at the top and bottom of each coil. Is that the correct place to measure from? For the coil in the photo on the right, I measured about 4 ohms. The other tests as open.

 

[Nashou66]

I would remove one connection of each to measure properly with out having anything else in the circuit affecting it.

Athanasios

 

[electro-diy]

I tried that tonight and both test as open (actually rather than the same 2 from the post above, I tested the one in the left photo and another one that was easier to access). I'm still concerned that I might be doing this wrong and don't want to go replacing things if not needed. Here's another photo. I cut the wires at Point A and tested that coil with one probe on the terminal at A and the other on the same coil at B.

For the other coil, I pulled the wire loose from Pt. C and tested that coil with one probe on the loose wire and the other at Pt. D.

Are those the right test points? And, if so, does that mean I should remove and replace these coils? - Thanks

 

[BillWojo]

Coils don't go bad unless they are damaged or had to much current passing through and burnt through a wrap of wire. Either is easy to spot with the eye. Third possibility is corrosion ate through a winding but those look dipped in wax.
Maybe show us your meter settings, I suspect something is not setup properly.

BillWojo

 

[gadget73]

these look to be oscillator or antenna coils in a tuner, agree they very rarely experience problems, and they should not be carrying any current to speak of. Often if they are going to break, it will be right at the end where the fine lead attaches to the terminal or where it comes up out of the core and makes a sharp bend.

I wouldn't unsolder these either, it should read through the leads just fine. Messing with these is quite likely to cause damage.

Why are you looking to test these exactly ?

 

[electro-diy]

These coils are in a signal generator. The generator currently only puts out a sine wave between 24-30kHz so I thought the coils might be the problem. The exterior shows signs of having been wet and the interior has a lot of rust.

 

[gadget73]

possible they corroded then, if they read open circuit something isn't right. It should be a handful of ohms.

Probably not going to find an off the shelf replacement but it wouldn't be that hard to re-wind if needed. Just need to ID the wire size and turns count, then re-wind the coil to match. I'm assuming there is a trimmer somewhere to fine-tune the sig gen so the dial is correct, likely going to have to tweak that adjustment a bit too.