Zenith 24h20 Porthole

[bandersen]

Nice troubleshooting and fix

[leadlike]

I can only make a quick post, but perhaps someone here will know:

I can't get vertical lock, I will cover some of the other details on this later, but one of the components in the vertical includes a mysterious "vertical integrator" the parts list only describes it as this, and the schematic includes no values as to what is in this part. Anyone with any ideas on what Zenith used to make their vertical integrators?

[wa2ise]

Originally Posted by leadlike

Anyone with any ideas on what Zenith used to make their vertical integrators?

They tended to use this circuit

The resistor part tends to drift to too high resistance.

[leadlike]

Thanks! I may wind up making a new one.

Measuring voltages, everything comes up normal, with the exception of the plate of the vertical oscillator is way too low: I'm getting 45 volts on my digital multimeter, when my Rider's schematic puts it at 74 volts. The plate is only two resistors away from the B+ feed, so I replaced them as they were out of tolerance, but still get the same low voltage. Swapping tubes has no effect, either.

As it is, the picture I get "floats" vertically, it does a half-hearted attempt to lock, before drifting away again. The vertical flipping doesn't increase in frequency, there just doesn't seem to be any lock. Interlace is also poor. The effect is the same whether injecting signal at the video grid or through the antenna.