[old_tv_nut]

The rainbow stripes are at a frequency that is the difference between the color burst frequency and the color oscillator in the TV. This difference is a "beat frequency." The term comes originally from sound and musical instrument tuning.

As you tune the color oscillator, you will see the beat frequency change, visible as the number of rainbow stripes. As you get closer to zero difference between the burst and the oscillator, the number of stripes will decrease and they will get broader. If you get close to zero beat (meaning the oscillator frequency is close to the burst frequency), the phase lock loop should pull in and stabilize the color, but if the detector or control circuit aren't operating, it will be unstable, and you will see the hue of the whole image change randomly. As you continue tuning the oscillator from too high to too low (or vice-versa), the number of stripes will increase again.

So, with point J grounded, there is no control voltage, and you should be able to tune the oscillator from too low to too high (or vice-versa) with zero beat somewhere in the middle.

With point J ungrounded, if the phase detector is working, a scope will show a sine wave at the beat frequency (of a couple hundred Hz or less) at point J. This corresponds to the rainbow stripes of color phase you see in the picture, because the oscillator frequency is off from the burst frequency by this much.

I looked for a good illustration on YouTube, but couldn't find one, so I hope my verbal description is understandable.