got this one a while ago. Metal cabinet, the orig problem was a shorted bypass disk cap that was taking out the B+. New cap and new power resistor got it back up and running. Rather than the normal shot gun recap I decided to keep this one as orig as possible, the idea being I wanted to get better as trouble shooting. It only has a couple HV ceramic tubed paper caps, two filter cans and a handfull of smaller black electro caps. After watching for a while the 1st defect that happened was in the AGC, got super critical, sure enough one of those 4mf single electros was open.

Todays problem has been presenting for while, there was a bit of a smear in the pic to the right, would get better after being on for a while, which was a clue. I checked the schematic and there was a 50uf in the cathode circuit of the video amp. Normally I assume when this goes open you just lose gain on the Y signal and you lose contrast and get a weak pic. In this case the contrast worked fine so I had not suspected that one. I used a technique described by VK member CTC17 that uses an audio signal passed thru the suspect cap, sure enough it sounded weak an muted. I tacked on a new cap and the smear was cleared. I found the cathode bypass cap in the audio tube was weak as well (the set did seem a little weak in audio) so replace that one as well.

Next up was it had developed a case of the bends so I checked the filter caps. The audio test was not conclusive as they passed sound but my ear is just not that well calibrated. I tacked on a couple 80ufs one the two main filter caps (the one before and after the choke). this cleared up the bends so I will have to rebuild those cans for a proper fix.

the only remaining problem is the tint control. It seems to lack the ability to drive the screen to the green, it goes to purple no problem. as I turn towards green, the color shift some, but it also starts to lose color gain.

fortunity its has range enough for perfect skin tone, but its not righ. I did try adj the phase coil that the tint control connect to, I can shift the purple more or less but it does not add to the green. There is a .01 cap that couples the tint control to the phasing coil, I replaced it think it may have been leaky, but not effect. Its not the pot on the hue or the connection of the pot to the chassis as those would be a green shift.

going to try a new 6JU8 but it tested fine. going to try doing some VTVM checks around the burst amp and chroma sync phase detector.

If you have the Sams for it, do the chroma bandpass alignment. Sounds like one demodulator is being driven more than the other, that would not be a phasing coil issue but rather an issue with the transformer coupling the local oscillator to the demods. One is probably peaked higher than the other. If it's anything like other chassis, the proceedure will go something like this:

using the VTVM on the CW driver trans, peak for maximum output

Or something to that effect. Once the local osc has equal output to the demods, you should zero beat the osc and make sure the phase detector is doing it's job.

Could also be CRT greyscale, if one gun isn't set right, it can have the effect of not making the correct colors on screen. Use the service switch, adjust for B&W.

grey scale ok. have sams, will look into chroma alignment.

the color hue is actually just right, it just lacks the ability to go too far green. this set uses two 6ME8's a single tube taht does both the demodulating and the output to the CRT. as you turn from too purple to just right (center of hue) and continue it starts to get just a bit too green, but then thats it, continue CW and the hue stays the same (just right) but the overall color gain goes down somewhat. Guess I should double check that pot, the CW turn is going away from ground, maybe it opens up completely, but I figured that would cause a much bigger problem.

hmmm closer look at that smear cap, the cap not just bypassing the cathode of the video amp but it was also connected thru a choke/resistor to the collector of the video amp transistor, perhaps a decoupler of some kind. Perhaps that is where the smearing was coming from.

anyway back to it in a bit, will start by checking the hue pot again with an analog VOM. then will check the voltages around the phase detector and some resistors that show as 2.2 meg matched. If all that checks out I will review the chroma setup. I hesitate to go there since I can see why it would need adjustment, unless someone fooled with it I suppose.

going to read some more case historys, I seem to recall something like this tied to a problem on one of the 3 legged disc caps.

I read up somewhere about a defective 12pf cap on the plate of the burst amp tube, so I clipped in a 6pf just for fun, the hue shift was to the green now. I readjusted the phasing coil and was able to get a good purple to green shift. So I removed the 6pf and tried resetting the phasing coil again, this time I am able to get a decent purple to green shift. I have a feeling that cap has drifted, its a 5% and has a N220 rating which IIRC is a neg temp co-effiecent. I think the 1st time I tried it I just did not turn quite enough. Now when shifted to either extreme (green or purple) of hue the color gain seems to drop about the same. Not sure if this is normal using these 6ME8 tubes. I will have to check and see if my other Zeniths using these tubes do the same. Its not drastic, but you can clearly see the color gain increase when the hue is set to the middle (best flesh tone).

Doesn't anyone use a scope to check filters? Way quicker.

I have one, but my shop is in a bit of a shambles, I figured the filter caps were bad, the tacking in of some new ones confirmed more quickly than digging out the scope. The audio check works real well on smaller caps, sort of a poor mans ESR meter.

dug out my cap supply, have enough to make up some new filter caps. I have a few extra bases as well, it take a 3 section and a 4 section so I will prebuild the replacements, not have to worry if I break off the twist locks.

I have to take another look at the pin cushion correction. The bottom is not as good as the top, maybe thats just the way it is. IIRC this set uses a pulse from the fly and a 6KT8 tube to control how it gets applied to the yoke for bottom and top pincushion correction. I will try a new 6KT8 1st. The phasing is adjustable but not the amplitude. there are a few 10% caps in the circuit.

look at the filters. Look for the 22- #. I may have those left as OEM.