Zenith Console combo

[old_coot88]

Originally Posted by 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...

First off, those coil forms that Zenith used tend to crystalize from heat and fall apart after a few years. If yours haven't fallen apart, the set is probably very low time. Also, concerning one of those blue coils (forget which one, been a lotta years), if you run the slug too far out (or if the slug is missing), it will fry one of the wirewound pots. This is probably what's happened in your case.

For that stripped slug, you could take a very thin strip of rubber from a bike inner tube (but not a gum rubberband which will rot) and lay it full length inside the form, then push the slug in. The strip will provide a friction fit and you can still adjust the slug as needed.

You might consider a small muffin fan to keep the conv. board cool, to slow deterioration of those coil forms. BTW, RCA conv. boards will also smoke a pot if one of the blue slugs is turned too far out. A little tidbit worth bookmarking. Bill(oc)

[DaveWM]

Great info OC, this is something that needs to be passed on to the current crop of TV restorers. I will go back and check that slug. I am still getting the hang of convergence, I just read up that perfect convergence on the side is just not going to happen (example blues bend down). I notice that old show that dont have a lot of text just seem to work better.

here are some pics, I have since these were taken worked a bit on the lower blue horz for some improvement.

[DaveWM]

OC, I checked that pot, it was indeed hot. I ran the slug in some seemed to help it, but of course it also goofed the horz blue convergence on the right side a lot. So I set it up so the slug was not as far out as I started and comprimized on the pot setting for best blue convergence horz left and right. Its still pretty hot.

[DaveWM]

Originally Posted by old_coot88

First off, those coil forms that Zenith used tend to crystalize from heat and fall apart after a few years. If yours haven't fallen apart, the set is probably very low time. Also, concerning one of those blue coils (forget which one, been a lotta years), if you run the slug too far out (or if the slug is missing), it will fry one of the wirewound pots. This is probably what's happened in your case.

For that stripped slug, you could take a very thin strip of rubber from a bike inner tube (but not a gum rubberband which will rot) and lay it full length inside the form, then push the slug in. The strip will provide a friction fit and you can still adjust the slug as needed.

You might consider a small muffin fan to keep the conv. board cool, to slow deterioration of those coil forms. BTW, RCA conv. boards will also smoke a pot if one of the blue slugs is turned too far out. A little tidbit worth bookmarking. Bill(oc)

I ended up destroying the coil, but was able to find another coil (diff winding) which I removed all the old windings, so I just had the form. Then I removed all the old wire from the messed up coil and rewound on to the donor coil form. Put it all back in and it works great. The donor coil form plastic is in much better shape and the slug moves very smoothly.

[old_coot88]

Originally Posted by DaveWM

I ended up destroying the coil, but was able to find another coil (diff winding) which I removed all the old windings, so I just had the form. Then I removed all the old wire from the messed up coil and rewound on to the donor coil form. Put it all back in and it works great. The donor coil form plastic is in much better shape and the slug moves very smoothly.

Cool! Good job Does the pot run cooler now, and is the convergence better?

[DaveWM]

the only thing I have left to do is to find a 4 by 6 speaker to go in the TV speaker hole. As is it has a switch that cuts out the stereo and routes the TV amp tube output to the main stereo speakers. Works ok, but I would much rather have the option of power the TV audio thru the tape input (aux) and bypass the TV tuneer completly for audio. I have done this on a maggie astrosonic tv and it sounds great. I tried it out already (to check levels on the aux input to the convert box output, all fine).

The only reason I want the small speaker is on the off chance I get a UHF channel that is OTA and need the analog tuner for sound. Also I dont like the idea of disabling the audio completely, as it would no doubt be confusing to any one that gets this thing some were down the road. I will of course leave all the wiring harness in place so it can be converted back to the orig setup.

I will check around my stash and see if I can find that 4x6. I check the mounting with a scrap speaker (cone shot to heck), it has some nubs that just barely are long enough to do the job. They are not machined, more like locating pins, but I can not see any thing to screw into. I will prob just silcone in the speaker around those nubs or see if I can find some of those star washers, the kind that push on but don't come off. Not sure if the pins are long enough for them.

[DaveWM]

well I decided to take one more stab at the HV regulation..

I have the "early" production version of the 20C1x38 chassis, my service notes showed the changes from the early to the late, one of which was HV regulation

I rewired the HV pot per the late version. the only diff was the output from the varistor was directed to the unused side of the pot, and the input for the grid bias of the 6HS5 tube was moved to the center wiper. the 1 meg resistor was left in place. This results in the pot as a true voltage divder (+ one side, ground thru the 1 meg on the other) rather than acting like a reostat with only one side and the wiper in the circuit.

I also added a second varistor piggy backed to the replacement (actually I just reused the old one I had taken out) This was done on the top of the chassis after the initial trial did not have good range.

I had tried the piggy back method before the rewire of the pot and it did not help much, some but not much. So I know the rewire was the key.

I am not able to dial in the HV to the exact amount specified and its very near the middle of the pot setting.

My guess is the varistors are not very precise, I know this since I tried a few by just putting them to a mA meter and dialing in up to 450v. They were very different readings for the several SAME rated ones I tried. These were NOS so dont know if they just age poorly or if its just the way it is.

But now I am happy, I get rock solid HV (very little movement regardless of the screen brighness) and I am able to lock it in right at 24.5kv.

I just have to work that speaker issue out and I can button it up for good.

[DaveWM]

Today I picked up some 3 conductor wire and varios spades/lugs, and made up a speaker hookup to bypass the factory wire harness that incorporates a stereo cut out built into the TV on off.

I also hooked up a nice little zenith 4X6 speaker (the front bezel has a place for it and the speaker slots are open). I just need to find some star washers to hold the speaker in place, will look tomorrow.

So now you can turn on the TV, and turn up the volume to listen thru the little front speaker OR hook up L and R audio from the DVD or converter box, drive the Tape in and listen to the audio using the built in stereo amp.

MUCH nicer this way, I figure if I am going to be watching on a 40 year old CRT I can at least max out the audio.

I was watching the new star trek movie (kid kirk driving the stringray corvette) when he had on the head banging music, it rocked...

after I get the speaker secured I will get started on my last console in the que, a CTC 17 combo.

oh yea I just left the orig harness in place so it would be very easy to put it back to factory orig setup.