21-CT-55 power supply failure

[Penthode]

Originally Posted by miniman82

I'm beginning to notice there are some issues with the horizontal oscillator. Pin 5 is right where it should be at 270, but the grid is sitting at -65 when it should be around -85. This in theory would cause the tube to conduct harder, leading to an increase in output waveform, which could in turn overdrive the HOT.

I have a gut feeling the horizontal oscillator fault is not related. The Horizontal and vertical sweep sections get their power directly from the 400v line.

The +285v line appears to feed only the luma, chroma, sync and RF unit (tuner). I assume you injected a baseband composite signal at TP101?

As a curious subnote, I noticed on my RCA Service bulletin for this set (First Edition-First Printing 11-24-54) that the connections to the RF Unit to the main chassis do not match. Connections 2 and 3 are reversed! Funny, it has to do with the +285v supply and the other is the 6.3vac filament connection. Do you see the same on your schematic?

I do not see a particular single point of failure on the 285v line which stands out. Can you reaffirm that you see a full color image when it is injected the baseband video?

I would guess that maybe another electrolytic has bitten the dust? Some more voltage measurements are in order. Good luck and we will look forward to the next installment.