1968 Zenith 20Y1C50 chassis - advice needed

[Jeffhs]

Originally Posted by joe111671

The 6HS5 regulator tube finally came. I installed it, and the new HV adjust pot (minus that resistor that was across the old one). The HV is now adjustable and I was able to set it to 25KV so I'm happy with that. Only thing now is the 750v boost is still too high at 903 volts. Not sure why, but it still has those white elemenco caps on the 750v, so I'll change them since I have them and see what happens.

The tube that was in there was a 6JD5, didn't notice that at first and have no idea if that was contributing to the unadjustable HV, or if it was just bad.

So far this set needed a good cleaning, a cap in the contrast circuit, a new focus stick, new resistor off the HV reg tube that was burnt, and HV reg tube. The HV cage was dirty, and cap on the rectifier tube had green corrosion and was causing sizzling in there.

The HV adjust pot and VDR may or may not have been bad but they're new, so all good there.

The tint is worse than before. I have the control all the way to one end and the flesh tones are still too red. It still needs the degaussing thermistor and the convergence is pretty bad, but it's working!

The convergence doesn't look too bad on the thumbnail image you posted. The tint control should be at mid-range to produce normal flesh tones, with said tones being red and green at either end of the control's rotation. The 3.58-MHz color burst oscillator tube may be weak; I would replace it before doing anything drastic. The chances are this will center the tint control, but if not, set the control at midrange, then tweak the color burst phase adjustment until the flesh tones are normal.

BTW, your set needed a good cleaning in the worst way, especially if you found green corrosion on the plate cap of the HV rectifier; that would explain the sizzling sound within the HV cage. It was a good thing you replaced the HV adjustment control, as it may have been dirty and/or had bad spots on the carbon track; if the latter, you could have had intermittent high voltage and/or moderate to severe arcing. Since color TVs using CRTs generated extremely high (by b&w TV standards) second-anode (ultor) voltages, it is entirely possible, even likely, your set's HV adjust control was arcing internally. If so, I'm surprised the HV fuse (or even the TV's own line fuse) didn't blow immediately, as soon as the arcing started.

As for the VDR, however, I'm not sure. Your Zenith TV was made in the late 1960s; it surprises me that Zenith was designing their color TVs with VDRs at that time. I would not have expected to find a VDR in a color TV from that particular time frame; in fact, I'm all but amazed any make of TV even had VDRs, in the HV plant or elsewhere in or on the chassis, at that time. Zenith must have been well ahead of its time when the company designed and built your set. I had relatives, now long since deceased, who owned a Zenith color set similar to yours; they liked it, and it worked very well, as long as they had it. The only major problem they ever had with that set was when the CRT screen cracked, diagonally, probably due to a design flaw (this occurred about six months or so after they had purchased the TV); once the tube was replaced, under warranty of course, the set worked very well for them for years, until it was eventually replaced by another Zenith 25" console.