another zenith combo

[DaveWM]

picked this up today, owner displayed raster, has a bad case of magnatized screen, I hope the deqausser will clear it up, and its not a bend shadow mask.

The finish is in very good shape, I had planned to scrap it out and save the chsssis for a parts set (has good stereo and phono as well) but its so nice that I may end up just keeping as is.

[Dan Starnes]

Love it!!

[sampson159]

save the cassis?save the entire set!this is a keeper and before you tear it apart,let someone take it to preserve the whole unit.if you were closer,it would be me!

[DaveWM]

its safe for now, I had hoped the finish would be bad but its in good shape.

[DaveWM]

got it out of the back of the X, only got a charlie horse in one arm.


since it had been turned on before, and from what I understand from the orig owner (granny passed away) it had been used reg up to a year ago, I skipped my normal routine (HOT/VOT out variac slowly).

color is VERY weak but working (hues good etc...) but you have to be on the ragged edge of the fine tuning to get it to come in, and the color level all the the way up.

No ghost or any other nonsence, so I will start by checking the color circuit tubes, maybe the AGC as well (contrast it all the way up).

the degausser got rid of the magnatized screen so the shadow maske was ok.

I will check the built in degusser, so far every set from that era has had a busted thermistor (down to my last CL90).

Needless to say its VERY dusty inside so I will put on my dust mask and blow it out so I can see what I am doing.

Tested the CRT tested very good, excellant tracking and good emissions even at 5v on the filaments. Of course the little CRT pin guide broke but I have a couple extra that I can put on if I can get the base off. Or I will just super glue, but its not a big deal. the pins on the crt looked pretty corroded (had some green on them) so I am pretty sure the tubes will need a good pin cleaning as well as the sockets.

Stereo works but needs some attention to the controls, Phono will need to be cycled a few times to see if the mechnicals can work them selves out, it would not turn off but that is prob just lack of use and or lube. this turntable seems to rely a lot on gravity to move all the parts into place in operation, I like the magnavox TT much better.

[DaveWM]

it had a few weak tubes, the color burst and color amp, replaced both helped some but still way too weak. Cant find my long handled flat screw driver to adj the AGC, so will hold off on anything else until I do that.

I will review the service notes, and take some voltage readings, starting with the cathode and grid voltages of the CRT.

Looks like I may need to touch up the audio quadrture coil (after I sub the
6Z10 tube) the audio is weak until you again get right at the ragged edge of the fine tuning.

I suppose it could be something amiss in the IF, although all the tubes checked fine.

but 1st thing will be that AGC, I have had enough issues with keyed agc to make sure its right 1st.

[DaveWM]

interesting that the audio/color are both affected by the fine tune (have to have both right at the very edge of pic interference). Other sets are not the sensitive in the audio at least, this one has zero audio right up to the ragged edge.

[DaveWM]

last nite I put my B&K 1076 on a working zenith with good color, attached the RF lead to the ant, turn color bars on, video image off, and scoped the output of the detector. I just wanted to see the waveform and the PP (approx 2v). So next I will duplicate the setup on the new zenith with the weak color and see if I get the same results. At this point I just want to make sure I am getting a decent signal thru the IF.


I think it may be a signal issue since I not only have soft color but a weak vert lock and weak audio.

[DaveWM]

Next if the PP looks good I will sweep it just to see the IF curve, again checking against a working set, as I know that setup and AGC voltage can have HUGE effects on the bandpass curve.

I dont know if this the the fastest way to trouble shoot, but since I am not in it to make money, its a nice learning exp, and gets me more up on how my test equip works.

I dont really know what the "correct" method to trouble shoot this kind of issue would be, so for you techs out there feel free to advise.

so far I have have checked the tubes in the color and IF circuits, that's it.

I prob should as a min check the B+ and the AGC setup before I get too far into it.

[DaveWM]

after replacing the color amp tube/sound IF (both 6kT8's) and the 6Z10 audio out, the color and audio are MUCH better. Seems the more I run it the better it gets.

there is still some horz lin issues, and I need to check the cathode current (not that there is anything to adj, no eff coil on this one). My guess is a new HOT/Damper/horz osc will clear that up.

the color and tint pots are very dirty so I will most likey be pulling the chassis just to clean up those. While out I will clean on the tube socket pins, and check for out of spec parts. Its kind of a toss up as to should they be replaced, that is the set is working do I mess with it until its not...

the stereo pots are dirty, and I prob should at least replace the output caps (big 500uf 50v that drive the speakers) the AM is iffy, I am pretty sure it has some shorting plates in the VC.

[DaveWM]

well for practice I got the BK 417 setup and did a sweep on a working set, the IF curve looked a bit off, curve at the 42.67mhz was low, so rather than a flat topped with dip at 44 it was more a peak on one side of the 44 and low on the other. But the set works fine so it may just be something I am doing in the setup that is killing the gain in that part of the band.

I used a ungrounded tube shield on the osc tube (B+ pulled to the tuner) and set the AGC bias and RF output to avoid clipping.

I will have to try it on a couple other sets to see if the curve is any different.

Kinda good to do this now and then if for no other reason just to practice.

[DaveWM]

while reviewing some case historys on this chassis, mention was made of poor ground connection being made at plug that connects the hue/color pots to the chassis. too much green and weak color, both of which this chassis exhibits, so I will be pulling that plug to inspect. The only thing is EVERY zenith that I have touched that had that plug was stuck and a major pita getting it loose.

[Jeffhs]

Originally Posted by DaveWM

picked this up today, owner displayed raster, has a bad case of magnatized screen, I hope the deqausser will clear it up, and its not a bend shadow mask.

My RCA CTC185 table TV fell off its stand a couple years ago. When I put it back and powered it up again, the picture had color splotches all over the place, as if the CRT had become magnetized. This set has an auto degausser, so I thought that should have gotten rid of the impurities; however, it didn't. What did clear up the problem was a couple of sweeps around the screen with a magnet from an old speaker in my junk box. The shadow mask in my TV's CRT may have been bent just a bit when the TV hit the carpeted floor in my apartment, and the magnet may have straightened it out; the picture was like new when I powered the set on again. I don't know why this worked so well (I thought that the speaker magnet would remagnetize the CRT and make the problem much worse than it already was), but the important thing is it did work, and well. The same trick might (I emphasize might) work on the CRT in your set if the shadow mask is bent; I'd try it first before even thinking of getting a new tube -- CRTs for these older sets may be difficult or downright impossible to find in this age of flat-panel, HD, 3D (!) TVs, unless you can find a good used tube.

[DaveWM]

crt is fine, degausser fixed it right up.

[holmesuser01]

Unless a set has hit the floor, I've only seen one or two sets that had bent shadow masks.

I used to love hearing the description of the problem when a customer would bring in a set with a burned up degaussing circuit.

The words FIRE, and SMOKE, and STENCH were used often.