I have a couple of circuit boards that have a dual coil choke installed on both incoming power traces. Because the items are dead and non conductive I can't tell how they were wired to the pins.

 

They are common-mode chokes. There is one winding in series with live and one winding in series with neutral.

 

Two hots, 240vac, but understood. What is confusing is that the coils appear to be across the line rather than in series. I have some Bourns products that physically appear to match the damaged items on order. Selected base on VA of transformer and fuse sizing. I was looking at the 7300 series vertical. Not sure what the diagonal solid line is across the pins.

 

They should definitely be in series.
On the circuit diagram the diagonal line joins the lines that represent the magnetic core, to indicate that both coils share the same core.

 

Ok, so I got the part in that I thought would work. Based on the 7mm x 8mm hole pattern it is obvious which way it has to go in. Using my multi-meter I note that I have direct conductivity across the lines. Pins 1-2 and pins 3-4. Direct shorts. There is a large mega ohm resistance from one line, Pin 1, to pin 3 which is on the other line but across the gap. So I am having a hard time visualizing what the correct component is suppose to physically look like. Am I supposed to have one winding across each gap in the circuit board?

 

The device might be installed wrong!!! Those dual coil chokes have one section in series with each half of the line. THAT IS THE ONLY WAY THEY SHOULD EVER BE CONNECTED!! Connection in any other manner is WRONG!! Certainly a poorly advised person unable to understand the application may intentionally force an incorrect connection. (comment deleted).

 

The device might be installed wrong!!! Those dual coil chokes have one section in series with each half of the line. THAT IS THE ONLY WAY THEY SHOULD EVER BE CONNECTED!! Connection in any other manner is WRONG!! Certainly a poorly advised person unable to understand the application may intentionally force an incorrect connection. (comment deleted).

I agree with you. That pcb looks liked it was laid out wrongly. The holes are even symmetrically placed in the outline.
Someone misread the choke datasheet.

 

I now realize that the choke that I ordered is incorrect. Unfortunately I am not able to identify the original item as to manufacturer and they show open circuit anyway that I measure. Toaster overload. I have a couple of boards that have these chokes smoked. I suspect what takes them and the transformer out is an overload on the secondary side of the transformer. So I guess I need to find a choke that has the coils across pins 1-3 and pins 2-4. I have a ohm meter that is more sensitive than my Fluke. Maybe what I am seeing as direct short is the resistance of each coil.

 

Looking at the Coilcraft pdf it looks like I need a BU9S as the Bourns item I have appears to be wired like the BU9. I was using the VA rating of the transformer and the size of the fuse to determine choke current carrying capacity.

 

In many applications the PCB connections are done so that the wrong insertion does not fit. AND I suggest checking across the mains input before applying power the first time.

 

The Coilcraft CM choke looks to be the same as original where 1-4 are in series

The Bourns would appear to have same pin numbers but wired with connections rotated across line so it might interfere with fuse holder.

 

The Coilcraft CM choke looks to be the same as original where 1-4 are in series
View attachment 343101
The Bourns would appear to have same pin numbers but wired with connections rotated across line so it might interfere with fuse holder.

That drawing is wrong. 1 and 2 connect to one winding, 3 and 4 connect to the other.

 

If 1&2 are a coil and and the photo shows the AC traces across 1&2 then it seems you were right the AC input is across the coil but it is a design flaw as the impedance is in the ohms. So one of these assumptions is wrong. In any case the current must be in series with the coils.

 

The board does have a 7mm x 8mm hole pattern with the 8mm being the gap that the choke spans between the incoming lines and the transformer. The coils are across the 7mm dimension. The pencil on paper schematic was how the Bourns data sheet and the physical layout of the coils appeared. Noting comments it can not operate like the sketch.

 

In the first drawing the circuit shown does not match the physical drawing. So there is a quite serious error at that point.
I suggest verifying the actual connections before starting production.

 

 

Revised the sketch to match the board. What was confusing me was that the coils were physically 90° (as shown in back lit picture) to the traces feeding the transformer. Remember that I do not have good board to compare components to. This is a board with damaged components. Whatever took out the choke also took out the transformer. This board has two 1.25A fuses, on on each side of the transformer so it must have been a pretty good surge. Transformer wired in series is rated at 1.25A. Dead on the primary side which is were I normally find failure. From all the input it appears that I need a choke that is wired with the coils in series with the line traces. And has the current carrying capacity that matches or exceeds the fusing and transformer rating.