Kortek KT-1420A help needed

[obitus1990]

I have a KT-1420A that I obtained as non-working. I recapped it, and, it powered up, though with low B+, which was remedied by adjusting the B+ pot. I got an image, though unstable, and then the yoke started to smoke. It's definitely not the chassis, as I have it mounted away from the monitor frame by about 1 foot (as far away as it will reach without disturbing the wires), and was emanating from the underside of the yoke. I had read on an Aussie arcade forum that this monitor will develop yoke issues due to the type of rubber/adhesive used on the tube wedges for the yoke, so I removed the yoke and found some green corrosion in three areas. When checking the Ohms of the V and H windings, they are both within an Ohm or two of what they should be, according to repair guides I've read for this monitor. When I check for any breaks in the coils with the continuity setting of the meter, everything tests as continuous, even though I have cleaned off the green corrosion and found several breaks in windings. If there is an open winding, why does checking the two Horizontal or two Vertical loke leads not give me an OL reading on the multimeter?

Is this yoke toast?

Thanks!

 

[stj]

got pictures?

btw, a lot of kortek monitors are hantarex clones - could be usefull to know.

 

[obitus1990]

I can take a few this PM when I get home. The breaks I found are in the magnet wire that extends into the plastic shell of the yoke, facing the neck of the tube, versus being on the ferrites themselves.

 

[obitus1990]

The remaining green area is where the wires are broken.

 

[stj]

thats wrecked
not sure what could cause it though - the laq on the wires can withstand most chemicals

 

[nem]

When I check for any breaks in the coils with the continuity setting of the meter, everything tests as continuous, even though I have cleaned off the green corrosion and found several breaks in windings.

A shorted winding will still show continuity.

 

[obitus1990]

@nem, can you explain that to me? What would be shorted to what in this case? The two horizontal leads have continuity, and the two vertical leads have continuity, but, there is not continuity between the H & V sets (which I would think is how it is supposed to be, since they're separate).

Also, is the magnet wire that spans the internal aspect of the yoke also connected to the coil wires on the actual ferrites?

 

[Plymelk]

Do the Vertical windings and Horizontal windings read out of spec for this yoke? Not sure what those values are supposed to be (Resistance or Inductance) but I'd venture to say that information is out there with enough sleuthing.

 

[obitus1990]

@Plymelk no...the windings test within 1-2 Ohms of specs I found for it.

 

[stj]

ohms is pointless, the wire is so thick
you need to read the inductance

 

[obitus1990]

I'm not sure I have the proper tools to measure inductance, as it's something I've never had to do. Does that matter if the coils can be seen to be physically broken?

 

[stj]

if they are broken then obviously they wont meter correctly