Repair of 15″ MAGNAVOX P232 field coil woofer

In middle of 2013, I got a pair of 15″ Magnavox field type woofer units.
No holes, no dents no signs of repair in cone and edge, It looks perfect in a sight.
But unfortunately, one of them has a problem in field coil wire. It lost contact and shows 11.9M ohms resistance.
I write article about field coil repair.

This time I purchased a pair of Magnavox P232 15″. There are 4 frames in rear basket. I expected spider damper a bit, but It has usual gathered type damper.
There are many Stamp marks on the frame.
I can recognize 10526, 5200OHMS,　143,　31426?,　232 739,　1D2880.
So, manufacturer code is 232 (Magnavox)
Production year is year of 7 = 1947 (Maybe), 39th week of the year
This unit’s field coil has specs of 5200 ohms resistance, actual measurement of mormal unit shows 5300 ohms. Half broken unit shows around 11.9M ohms, but not stable if I touch wire at end of winding. It’s necessary to dismantle field coil and pull out copper wire.

I dismantled Field coil magnet of the unit.
First, I dismantled black color yoke frame.
You can see 4 pcs of Hex Bolt heads next to the damper.
Record the mounting position and orientation before remove 4 bolts.

If disassemble yoke back plate, then Pole piece come out together with yoke.
Then, coil was still staying to the yoke front plate, but it was free and not hold.

Detach coil, then you can see the small plate that is covering voice coil.
Take this small plate out, and expose voice coil.

Starting repair of contactless wire. It was very beautiful unit looks flawless.
I had to cut isolation paper which covers field coil.

I’d checked where the broken point is, and found most inside cable lose contact at the point of coil end.
There was no problem to through away the broken part of cable and shorten it. because this cable has several thousand turns length, 10 to 20 cm has really no effection to the field coil specs.
So, loosen winding for few turns, pull out the wire, cut, and solder to external cable.
(Broken point was at the center top of this photo, Black color clip is oposite side. This side has no problem)
After resolder, Resistor value is changed back to 5.32k ohms as almost same as the other unit.

Fix the isolation tape and papers back to the original position, repair of field coil was completed.
But unfortunately, outer isolation paper couldn’t be fixed nicely as original.
Assemble coil to the yoke again.

I noticed later on, there was a bit of “voice coil touch”, I needed to re-position the voice coil center one more time.