Zenith Console combo

[DaveWM]

boy this thing is kicking my butt. The new HOT tube fixed the squeal, but then I lost HV regulation (would bloom too easy, and the HV adj did nothing. Wide open with no beam current would be about 24k, but would drop to below 20k and be moving all over the place with the beam current. I also lost width. So I tried ANOTHER 6JS6 HOT, plenty of HV now, in fact all the way down and even with a bright screen its 25-27kv, too much really. Not sure I will try a couple more HOT's if I can find (I have a few pulls to try) but I may end up having to buy one. Oh and the width problem went away. Still now squeal so that is good. I may but that squeal tube back in and see how it goes.

I tried the purity setup, the yoke did not seem to go back far enough to get the red blob in the middle, so I just fiddled with the purity tabs to get the red centered as best as I could (most of the screen was red) then pushed forward to get it to cover the whole screen in red. Color purity looks good now. still some dynamic convergence to work on.

Still have not pulled the chassis to replace those few HV film caps.

[DaveWM]

progress, working on HV regulation with help from CTC17 (dan).

seems I can dial in the HOT current and HV with different HOT
s but the regualation is just not happening. will be checking the reg tube voltages tomorrow. the Plan is to replace the focus resistor (at the edge of adjustment now) and hope that effects how the regulator is working.

I had noticed the color was a bit weak, found a chroma amp screen grid resistor that had driffted up about 400% so that will get replace as well. while I have it out I will check the disk decoupler cap, just in case it was leaking, thereby stressing out the screen resistor. its just a little 82k 1/4 watt.

[DaveWM]

stopped by my tube guy, checked all the tubes on a 539 hickok, turned out the HV regulator tube was very weak (and yet looked brand new). I hope that helps resolved the regulation problem.

Today I replaced 3 resistors on that chroma amp tube, while checking the other tubes he thru in the syn/noise/agc tube, two color demodulators, a new audio tube (6z10), a 2 IF tubes (one shorted, the other very weak), and an RF amp tube (again very weak).

I also replaced the focus rectifier stick.

Cleaned the chassis top, inspected the ground stakes (two were cracked) and resolded.

Cleaned all the gunk around all the term strips/tube sockets, cleaned the tube socket pins (small nylon spiral brush and cleaning juice). cleaned all the tube pins (brass brush). Cleaned all the plug in sockets (hue/color, convergence, yoke) cleaned the CRT socket (sprial brush). Wiped off all the sticky goo from the wires (yoke, CRT, speaker).

inspected the bottom for any componets that may have been moved after working on the resistors, and transporting the chassis.

Cleaned up the fly back plate (dust, general nastyness) careful not to work behind it where you cant see the fine wires.

Still need to give the pots a quick shot of cleaner/lube, that is all the pots on the chassis front, and the volume pot.

the Thermistor is busted, every set I have seen has a busted thermistor. I have a CL90 but not sure if the rating is correct. Will do some checking and see.

[DaveWM]

looks like the CL-90 specs out at least to the cold resistance (120@25c) and since its in the B+ it should be fine current wise. I have used them on other things, but that was on the primary side of the power tranny to soften the blow to the power switch (fisher 400).

so the thermistor is in, but its getting late so I will have to wait till prob Sat to reinstall the chassis and see how it goes. wish me luck...

[batterymaker]

Sounds like you're almost done. So close I can taste it...

[ctc17]

The adjustment on the front labeled brightness limiter should really be 'bloom limiter'

[DaveWM]

whew.. lots to report

voltage regulation was not happening, I check the voltage at the grid and the cathode, should be 350/360 (-10v bias) was more like 375/300 or -75, so the shunt tube was completely cut off, not loading the fly at all, so no regulation. I checked everything there was to check but the VDR, no joy.

since there is no specs on the VDR I decide to just replace it. I found on that was suppose to be a cross, put it in, bingo regulation. I was able to get the grid voltage up to about 340 so a little low there, and I need to keep the HV set as low as it will go, that gets me to about 25kv.

I am going to check a couple more resistors and the boost voltage (yes replaced the focus diode that supplies the 900v boost that drives the regulation). I thought I checked them but will check again. I have another zenith set to compare to. there is a voltage divider in the fly cage that gets the focus voltage down from 5kv to the 900v so I will look there again. but at least its in the ball park now.


after I got it installed another problem popped up, color hum bars. Now it was fine before I pulled the chassis so I really doubt anything went bad.

after a few careful looks I found a rather large disc cap that seemed pushed down and possibly having a lead touch where it should not.

this is the only thing I really dont like about point to point wiring, esp with open bottom chassis. you have to be REAL careful about how you handle and transport the chassis.

anyway I moved the cap and the color hum bars are got, thank goodness.

I really like what zenith did on some of there 50's era tube sets, where there was a metal bottom plate. this not only shielded from EM radiaition, but prevented just this kind of problem, AND the chassi was much stiffer so less flexing and possible damage from that as well.

getting late so I will reinstall later in the week, but getting real close now.

Oh I also replaced some resistors that had gone out of spec on the chroma amp tube, that helped with the weak color (had to have the color turned all the way up).

Not too far to go

[old_coot88]

Originally Posted by DaveWM

...after I got it installed another problem popped up, color hum bars. Now it was fine before I pulled the chassis so I really doubt anything went bad.... anyway I moved the cap and the color hum bars are got, thank goodness.

Colored hum bars can be caused by residual ripple in the degauss coil. It could be an intermittent in the auto-degauss circuit. Might try wiggling stuff in that area if the problem shows up again. Bill(oc)

[DaveWM]

it's ok now OC, I found a cap (large disc) that had gotten moved and looks like one of the wires had come into contact with some it should not have. I repositioned the cap and the color hum bar is gone

I just hate when I create a problem. Needless to say I will just be that more careful when handling the chassis. I think the prob happened when I was transporting the chassis in the back of the SUV. I had a soft blanket to set it on thinking it would cushion it, but I think what happened is the chassis just settled down and the blanket pushed the caps up into the chassis.

next time I will set the chassis on a hard surface and then put that on a cushioned surface so I don't bounce it around.

I figure this was a rookie mistake, I will not repeat it.

Thanks for the heads up I will keep that in mind if it happens again (looking around the degausse).

[DaveWM]

I did find several changes made in the zenith color service manual talking about revisions to the HV regulation. Some had a 6.8meg resistor across the varisistor, and a change in a 1 meg to 2.0-2.4 meg resistor off the HV pot, part of which sets the voltage divider range.

The easy thing would be to 6.8meg across the VDR, esp since I could do it from the top fo the chassis on the exposed term strip.

the regulation is working but its range is very narrow (all most all CCW) again this may be due to the use of a non factory orig VDR (the only one I could find that the supplier said was a correct cross).

[DaveWM]

bridged the varistor with a 3.9meg resistor, get a bit closer to the correct bias. Found a weaker HOT, was able to get the cathode currrent down to about 230 vs 260 with a stronger one.

I wonder how a 6KD6 would work? I am out of 6JS6's to try, one was very weak 180ma but the width would not fill out.

Just for fun I am going to try a few different horz osc tubes to see if I can get it any lower. pic looks good.

[DaveWM]

ok button up time I need to go thru my stash of volume control knobs (did not have one when I got it), pretty sure I have one that will work.

Gonna put the orig stereo tuner back in since it has the correct wire harness and works at least as well as the backup I got off ebay.

wiped the insides clean of dust (WAF). I think I will make up a DPDT switch to swich out the speakers between the normal TV output and the stereo output so I can use the stereo amp drive thru the tape input and the decoder box audio out for true stereo. There is plenty of access holes not used on the back.

I managed to crack the back today ((&(*( it) then I tripped and my foot caught it. I will get some 1/8" ply (used in model building) to reinforce the crack, I hate when that happens. Slow setting epoxy should work well with the masonite. It really bugs me when I manage to break something that has gone undamaged for so long.... argh....

The pictrue is looking very nice, I did the grey scale setup per the sams.

It still needs convergence but I would rather do that once I have it inside and where it will be setup to watch.

Just need to make a place for it now

[DaveWM]

found the perfect volume knob, only thing is its so new looking that now the rest of the set looks shabby...

[DaveWM]

argh, green static magnet does nothing, turns ok must be broken inside, no movement at all.


dynamic weak, time to replace the diodes on the convergence board. the left side is not too bad, the right does not seem to work at all.

[DaveWM]

replaced the 4 diodes, put all back together, started the setup, some smoke, pull the board. The pot that was getting hot was the left blue horz. someone had jumpered a 47 ohm 2 watt resistor. I noticed it but decided to leave it be and try as is after the diode swap. Removed the wire jumper (was very sloppy), and replaced with a 50ohm WW resistor (all I had on hand). the resistor that was in there that had been jumped over just fell apart so my guess is it was high or open and the jumper was just being cheap, prob ok as long as the pot was not turned to far.

Convergence is MUCH better now, only issue I have is one of the right side coil forms is stripped (the slug just pushes thru.

I may pull the board again and see if I can find a inner threaded section to fit into the existing bore. Or I could just glue a non metalic extention to the ferrit slug, and wrap it with some wax paper or some other friction fit. Or just try and get it set and then tack glue a drop of white glue (just enough to hold it, so if it needs to be reset it would break free.

could use some idea from other that have had to deal with this...


Had some sync buzz, adj the quadrature coil got rid of that. The speaker cut out switch on the on off (disables the speaker from the stereo) is a bit dirty, so one speaker comes and goes, tweek the on of just a hair and it comes back.

I am going to try a direct video feed to compare the pic to that of the tuner RF pic. I tried this on the other zenith connecting the decoder box composite video signal to the test point C1 (output of video detector) but for some reason it did not work on that set so will be interesting to see if this chassis has the same problem. there was a +5vdc on that test point so I used a large cap to block the DC.