zenith porthole question

[Electronic M]

Originally Posted by old_tv_nut

Looks like it may be running at twice normal vertical rate (120 Hz instead of 60).

I was thinking half frequency, since double would result in the top half of the raster being scanned over the bottom half (which I've seen before).

The problem with vertical running off frequency usually is a result of RC timing components in the feed back/feed forward loop of the vertical osc/multivibrator circuit having drifted off speck or being replaced by the wrong value due to human error. Check all resistors in the V osc/output stage for out of tolerance duds. Replace any original capacitors in that area, and make sure your replacements are of the correct capacitance. I don't know if Zenith portholes use vertical osc transformers or not, but if it does check the transformer too.