1968 Zenith 20Y1C50 chassis - advice needed

[Electronic M]

I'm a little late to the party on this observation but sometimes when focus voltage is good but proper focus is unobtainable and picture is bright (especially if previous owners have been monkeying with it) it can be because the CRT G2 AKA screens are set too high...I had that on a Setchel Carlson monitor and was chasing my tail till I turned G2 down...That brought the HV way up and I had to readjust the regulator.

[zeno]

That looks pretty damn strong. The green may be a little off though.
Contrast looks good, almost as if its at max. Keep in mind these sets
wont show the high contrast of newer sets & keep a good pix.
They are meant to be used in a dimly lit room & not driven to the max.
BTW we used ECG sticks. ECG was a good quality sub line almost all
the time.
BTW#2 Flipping a set on its side will throw off the purity, thats normal.

73 Zeno
LFOD !

[joe111671]

Originally Posted by Electronic M

I'm a little late to the party on this observation but sometimes when focus voltage is good but proper focus is unobtainable and picture is bright (especially if previous owners have been monkeying with it) it can be because the CRT G2 AKA screens are set too high...I had that on a Setchel Carlson monitor and was chasing my tail till I turned G2 down...That brought the HV way up and I had to readjust the regulator.

I set the G2s in service mode for a barely visible line, so I believe they're good. I did have slight blue retrace lines at first, so they may have been set too high. I don't think I touched the focus after that though so maybe it needs a touchup. The good news is that it didn't take much to get a line on all 3 guns, not even half, so the CRT looks to be happy! I should get the HV set when it's straightened out, that's a good reminder. It's supposed to be 25KV, and it was 26 before I even worked out the focus and adjusted the G2s.

Originally Posted by zeno

That looks pretty damn strong. The green may be a little off though.
Contrast looks good, almost as if its at max. Keep in mind these sets
wont show the high contrast of newer sets & keep a good pix.
They are meant to be used in a dimly lit room & not driven to the max.
BTW we used ECG sticks. ECG was a good quality sub line almost all
the time.
BTW#2 Flipping a set on its side will throw off the purity, thats normal.

73 Zeno
LFOD !

I think the picture exaggerates the contrast. I'm almost certain it's too low. In any case, the contrast control has no effect whatsoever, so something is wrong there. I took some voltage measurements around the video output tube, and the values on the schematic vs. the actual readings are below.
All readings vary w/ brightness control, and Contrast control has little to no effect on any reading:

Pin 1 (connected to contrast pot) shows 10.5V. It's 10.7-0.5

Pin 2 shows 5.5v. It's 5.8-(-19v)

Pin 7 shows 300v. It's 280-390

Pin 8 shows 130v. It's 187-273

There are 2 electrolytics in the vicinity that I didn't touch yet. Can they cause an unresponsive contrast pot?

[joe111671]

I decided to try and answer my own question on those electrolytics since I already have them, and the 50uF C3 was directly connected to the contrast pot. I chopped it out, tested and it was open, and changing it made the difference. The contrast works great now.

Now the vertical, which always had a little bit of jumpiness to it for the first half minute or so after power up, is now constantly jumping/changing height/linearity. All this stuff must work together. So now I have a vertical thing to work out. I'm tempted to just change all the electrolytics at this point, but spending time on issues makes it rewarding to find the exact culprit.

Not sure what I'll do yet, but I'm happy to be bringing this thing back to life.

[joe111671]

I'm happy with today's progress. I permanently installed the main filter caps, they had been jumpered in and hanging by wires since I connected them. I wasn't going to try and restuff the cans, and to mount them near the cans would mean removing the chassis, which I don't want to do at this point. So I mounted them under the chassis as neatly as I could. I j-hooked a few and was able to make use of a couple empty solder cups for one of them which was my first experience working with them.

I labeled the ones that are nowhere near the cans for future easy identification.

Originally Posted by nasadowsk

Hissing isn't normal. Clean the HV box by the rect up.

Also got rid of the hissing in the HV cage. I took the tube out, cleaned everything really good, put the tube back in and it's nice and quiet now. Next thing is to adjust the HV.

I still have that vertical jitter. There are three electrolytics in the vertical circuit. I replaced one, that didn't make a difference. Desoldered the next one and jumped in a new one, didn't make a difference so I soldered the original back in. There's one left, but it's tied into an electrolytic in the horiz section, so I left that alone for now.