Zenith roundie centering
 

Hi!

My chassis is a 24NC31. Its a 66 model. There is about a half inch space at the bottom of the screen and would be cured if I could get the screen centered vertically.

This set uses "centering strings". I see them, on on top and bottom of the deflection yoke. I think I am using them right, by pulling one end of the string. No effect on the screen at all. Without pulling the deflection yoke off can anyone tell me how these strings are attached inside and why they are not responding?

Also, my focus is at the extreme end of its range. Do these high valued resistors go bad in the focus section?

Thanks!
Matt D

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not a centering problem
 

If you put a scope on the vert sweep signal you will probably find that it is chopped off. Could be a bad cap in the vert sweep circuit.

The oscilloscope is your friend.

Wow,

You say neither of the strings respond??

The strings (one for horiz and a separate one for vert) are each set as a loop, pulling on one side of the loop or the other should make the adjustment. I've seen people take the horiz loop in one hand and the vert loop in the other and pull on both to try to adjust them that way (which won't work).

In all my experience I think I only had 1 that didn't respond. File 13 time.

You may start looking for a replacement

In the meantime, fiddle with the height and linearity adjustments. If they don't work, got out the scope.

The resistors very much go bad in the focus circuit. However, check for corona on the tube socket. Check in a very dark room.

Hi Matt,

I thought there was a vertical centering adjustment behind one of the knobs on the control panel on the front of the tv. You would either have to remove a knob to get at it or it had a small hole in the center of the knob to get a small flat blade screwdriver into it to adjust it. The reason is that it may be located on a control with a dual pot that only has a hollow shaft for the main control that is identified. Some had the hole in the faceplate to get to the control but wasnt in with another control either and is flush with the chassis. Those usually arent marked and you need a longer flat blade screwdriver to get to them. Anybody more familiar on this model feel free to correct me as i'm only going by memory.

On the subject of the Focus resistors, yes they do go bad or change value as Doug has mentioned several times in his Zenith restorations and will give the symptoms you described. If i recall right he also mentioned those resistors can be difficult to locate also so be prepared. Good luck!
-Tony