vertical overscan in Zeneth color TV

That problem is almost always bad electrolytic capacitors near the vertical output IC.

I had an old Zenith a long while back with no vertical adjustment pot on the outside - but there was one on the inside. I opened it up and pushed a 3 inch or so length of PVC tube over the pot spindle (one size fitted, 3/8 in, I think.) Then I drilled a hole in the back so that the PVC tube poked out - voila! An accessible adjustment - worked fine. A bigger problem is horizontal scan - most TVs overscan horizontally and require the vertical to overscan, too, to get good circles. I've never found a good way to set the horizontal scan... unlike computer CRTs. Cheers, Roger PS. Usual disclaimers about dangerous TV voltages - if you don't know don't do it.

The problem is usually caused by electrolytic capacitors in the vertical amp section going bad from age.

Don't touch any adjustments. Have the set properly serviced.

Jerry G. ======

Thanks to everyone who tried to help except for Jerry G. who assumed I didn't know what I was doing so was no help! I was hoping some former Zenith tech would have the schematic for this model. I'll try the elect caps around the vertical, I already had to replace an open one in the sound path sound, so should have looked for that too. Please note when I say I replaced the IC and the capacitor, I myself did it!

Overscan problems can be due to excessive supply voltage to the vertical output. Some power supply designs output higher voltages as their electrolytics dry. However dry electrolytics get better when warm, so your overscan problem should reduce after a while. You should also be looking at bad solder joints, open resistors and bad potentiometers.