I have a 1971 Chroma color Hybrid that I purchased from DRH4683 several years back.
It has been having focus isues for most of the time I've owned it. The issues began with the focus lead arcing to a grounded strut it was touching. When I spotted the problem (it was the first case of arcing I ever needed to fix) I wrapped the arc point with several layers of electrical tape and that fixed the problem for a long time. I might add that I used the set as a daily driver for between a week and a month not realizing that the noise was arcing before repairing it.

This repair held for a long time before the focus got squirily again this time it was really bad, and I was busy for a long time and ran the set with bad focus (that would improve after around 30 minutes of operation) for over a month before getting to fixing it. The tape had gotten brittle and crispy so that time around I decided to use a strand of plastic fishing line tied to a strut a couple of inches away to pull the line away from anything it could arc to. This repair has been sucess full, but the focus has gradually been getting worse I added an aditional 4.7m ohm resistor in series with the one in the HV cage and was able to get razor sharp focus with the control maxed out.

Reciently the focus got bad again and I added a 6.8m resistor (this was during the reassenmling of the set after a cateracting) During the adding of that resistor I dripped a solder blob on to an above chassis terminal and shorted all but the 400V and up B+ lines. Amazingly the HV still worked despite the H osc. having no B+. After much trouble shooting of the horiz, section I realized what I did, cleared the B+ short and replaced a power resistor that the short had fried.

Afterwards the width was greatly reduced even with the "increase width" jumper in place it just barely fills the mask, but the focus was razor sharp.

That was a few months ago.... More reciently the focus has gotten lousy and does not come back in nomater how long I run it. I stopped using it in the last few days as there is now fairly loud arcing comeing form somewhere.

I'm planning to take this console out of the stack I have it in, and trouble shoot it soon, and I've been woried that my doubler is going bad, and if fixing the arcing don't help and my HV is right I will want to replace the doubler as process of elimination will leave it as the prime/only suspect. I have a spare Zenith doubler (pictured Below), But I don't know what part # my original is so I'm not sure if the spare is right or not.
http://i1095.photobucket.com/albums/i469/ElectronicMemory/DSCN1247.jpg
http://i1095.photobucket.com/albums/i469/ElectronicMemory/DSCN1249.jpg

According to the schematic the doubler in the set contains a 40m ohm resistor between the HV lead and focus lead, and a 200m ohm between the focus lead and the ground(it goes to ground through the 15m ohm focus pot in series with that afore mentioned 4.7m ohm resistor that I've been adding aditional resistors in series with) This is by memory so if I'm wrong or hard to understand I can post part of the schematic to clarify.

If you can offer further insight in to this trouble or preferably know what the internal wireing of my replacement is, Please feel free to chime in.

I have a 25cc50 here I have been using lately that has that exact problem. Im sure its that devider resistor you are holding. NTE makes a generic line of those, I think thats a HVD-3, moyers should have.

Im not quite following the issue that started the width problem, but, did you try changing the output tube? Its very easy to 'hurt' them resulting in extended warmup time and reduced width.

If any of my used spare HO tubes test better than the one in there I'll see what effect can be had by changing them. I believe that once I correct the centering the width will be sufficient for my tastes. I only mentioned that as it may be contributing to the issue as I believe the HV was higher before the B+ incident.

If the solder blob caused the tube to overheat the weakened tube could be responsible for the lack of width. I may not be understanding what happened and way off with what Im saying.

You can take that divider apart and you will see where its failed. Its a ceramic bar with some kind of resistive material in a spiral. There will be burns in the spiral.

BTW: that part in your hand is a HVD-4
300meg tapped at 50 meg

The HVD-3 is 240meg tapped at 40meg

I'm going to do some calculations later to see if the replacement I have is workable (I will want to fix my set fast once I have it down as it takes up a ton of realestate in my cramped bed room/work shop/collection display-store room (if I took out my 6 TV consoles and 3 radio consoles it would be very large).

The short in the B+ was through the pin-cushion transformer (if memory serves) to a terminal then through a carelessly dripped blob of solder to ground. The short made the old power resistor smoke, open, and crumble. And what is more before I realized there was a short I put a dale type in place of the origional power resistor and it exploded! That can not possibly be good for the pincushion coil....

I wonder if the reduced width was related to either the pin-cushion coil, or my desoldering and resoldering of the components (at least one resistor had bubling wax on it's case from the heat, and the ceramic around the leads crumbled on a couple of the ceramic caps) on the output tube that led me to find the dead B+ lines.

Gota run.

I now have the set off the top of it's stack and am trouble shooting it so I decided to revive my thread.

The old girl is doing some funny things. First off the screen is intermitantly going dark for VERY brief intervals (blink of an eye brief). HV is steady at about 24.4-25KV.

The CRT socket it ticking!:yikes: I can't see any arcing in the vicinity of the focus lead in the socket, but that sound is a dead give away. Is it possible/reasonable for a socket on a 1971 Zenith to arc? What voltage from the focus lead is the socket meant to with stand? It currently has a solid 7KV or more on it when it should have only 4.1KV according to the schematic. When I first powered up the set the focus was at arround 1KV but now tends to stay up at 7KV....I find this wierd because previous issues were all stuff dragging down the voltage, and were eventually compensated for by modifying the set to increase the focus voltage to return it to speck. I wonder if whatever was causing the voltage to be low has cleared up, and if removing my mods will fix it.

There is also very loud intermitant corona at a solder terminal that the focus lead goes to in the HV cage.

I'm going to try some things.

Anyone have any potentially helpful ideas or oppinions on this that they would like to share?

Sounds like that old divider is buying the farm, probably shorting slowly causing a reduced internal resistance.

some of the Zenith's had a spark gap built into the crt socket that failed. Remove the metal grounding strap and see if the acring subsides. If so, the spark gap took a dump.

If by metal mounting strap you mean that piece of metal that runs form the socket the the spot that it clamps onto the grounded metal CRT shield, that was the first thing I disconnected to try and stop the arcing last night. It did not help.

A few months back I modified the focus control leg of the divider to increase the HV to meet spec. I'm going to reverse this mod in a few minutes and see if the focus drops back to speck.

Change the divider, 7kv is way to high and the spark gap is probably arcing. The spark gaps are there to protect the crt from issues exactly like this.

You meter is probably loading it down a few kv so it really close to 10kv

i had a divider go on my daily watched 1973 16 inch zenith portable a few months ago - started off with ticking, ended up in total loss of focus. If it's making noise, it is bad... Don't pass go, don't collect 200 dollars just swap it outFound one nos, changed it out, and back 'on the road'

Well here is a schematic of my old mods.
http://i1095.photobucket.com/albums/i469/ElectronicMemory/DSCN1317.jpg
The divider is in the dashed line box.
The modification that I noted in was added a few weeks before the trouble began(well the extra 4.7 meg was there months before, but the 6.8 was new and a lower wattage than the rest), and the resistors I added to the print are mega ohm post fix units. Early this afternoon I shorted across the 6.8 meg that was modded in and the focus droped to around 3.5KV so I think the 6.8meg is going high/open and causing the focus to sky rocket. shorting either of the 4.7meg units had no effect which I think helps proove the previous statement. I wish my DMM could read resistance above 2meg ohm as that would be very helpfull.

I wish I had the right divider on hand to try and swap, but I don't nor do I have time to order one and wait for it to arrive in the mail. Working or not this set takes up too much floor space when it is out of it's stack for me to allow it to stay on the floor for long. Plus I only have a coulpe of days left to work on it before my next quarter begins at my college which will kill all my time for me.

Since I can get the voltage to drop from excessive to just a tad too low I should be able to tweak my mod for perfect focus by replacing the bad 6.8meg with someting similar from my parts bins. I'll probably invest in a new divider soon so if I have another failure I can try a new divider.

I'll tweak my mod and report back.

Check the voltage ratings on the resistors you are adding. The HV divider is specifically designed for high operating volts, but most typical resistors aren't designed for a voltage greater than about 500dc, regardless of the wattage rating.

If you look at spec sheets from ohmite, etc for resistors similar to the ones you are using, you'll see what I mean. I say throw in an order for the correct divider, or put a wanted classified on here, and fix the TV over xmas holidays, or whenever the next break is.

The resistor that comes off of the focus pot and goes to ground is an old school 2 watt carbon comp resistor and that was the factory component. My only meg ohm rated replacements are also old school 2 watt carbon comp units that are of unknown vintage and manufactuer so I can't realistically check the speck sheets. The 6.8 meg unit that failed was a 1 watt unit, and I should have stuck with 2 watt, that is where I was dumb. My best solution presently is to use some 2 watters and some 1 watters. With the 1 watters being of equal value in parallel with each other so to divide the current equally among the two and make a pair of 1 watters behave as a two watter.

Right now with the focus control maxed out I've got 4KV and almost good enough focus. I'm going to add one more resistor so the best point will be in the controls range and do my best to make it fit the HV cage safely. I have just enough resistors to pull off this jury rig.

This will be a "till we meet again" kludge repair which I anticipate will last between two weeks and two years based on the sets track record. I WILL track down a new divider as soon as I finish my kludge and have it ready to drop in before the next failure, god willing.

I suspected that the divider was slowly going bad, but I could not prove it, and what is more I did not think that replcements were obtainable untill reciently. So now that I believe that I can get a new divider I will track one down, and install it the next chance I get after the next time it starts to act up.

I'll elaborate on what I've done soon.

I usually put an ECG-526A type tripler, and remove the focus divider altogether. I don't recall the exact mods, but it's easy. You also eliminate the 2-wire anode lead and cap that way. The 526A has a focus tap and a terminal on the for focus pot.

Charles

I just wanted to add my 2 cents. Charles is correct for a modified tripler, or find the EXACT focus divider replacement part.
High voltage is something one should never f**k with. I've seen other posts where some will try to use silicone, or high-voltage dope, or tape, or modify a part of the same brand, but not for that set.
Never a good idea........ It's a fire hazard, or could cause more extensive damage to the set. The engineers used the parts for that chassis for a reason.

Fraid I don't get what is meant by a trippler modification in the last post.

I finished my work on her yesterday I replaced the 6.8 meg 1 watt resistor in my mod by taking four 6.8 meg 1 watt units and wireing the four as two paralel pairs efffectively making four 6.8 meg 1 wattters into two 3.4 meg 2 watters I then put these two in series with eachother and used them as a replacement for the 6.8 meg unit in my old mod. This restored the focus to working nicely.

While I was in there I took the time to examine the horizontal output tube. The first thing I noticed was that the yoke cable was touching that tube, and on closer examination it was clear that 3 of the wires had the insulation chared off at the contact point (a major short waiting to happen). So I electrical taped the bad spots and dressed the wire about two inches away from the tube. I could not get it farther as the cable is short and the chassis is laid out such that they practically force the wire to touch the tube.:nono: I found out why the width was low it was indede the H output tube (type 6LB6 BTW) I had two spares one was labeled and the other was not, but the other tested good and had the same pinout so when the labeled one started glowing blue in the lower interior and causing a bad pin cusion I tried the other tube and it worked well. I was able to bring the width jumper back to the "normal" position from the "increase" position with plenty of overscan so I'm happy.

The output tube that was in there these past few months was testing at around 80 initally on my B&K 606, but quickly droping to 65 which is the upper border of the "?" zone. The new (well good used to be technical) one in there is rock solid at 92 so I now have a healthy tube in there.

I also had to relpace the original damper because to access where I made the mod I had to remove the tube and few mods and tests later I noticed that one of the damper pins stayed in the socket after I had pulled out the tube:eek:

we got rid of those focus blocks and used 526 triplers too.actually our supplier gave us a better deal on the 526s.they were less than the focus blocks.in a pinch,you can use a 556.not sure about the longevity but we replaced a few with those.they didnt come back!that was back in the shop days and did we experiment.dave was very detail oriented and kept notes on everything.i could publish a book with his notes.thousands of pages

What did you connect the tripplers to asside from the focus lead? I would think that in Zenith pulse regulator HV system sets the plate lead of the HO tube would fluctuate too much to derive a focus voltage from.

I believe that the socket is arcing and not just to the spark gap.....This set has a problem with the color taking too long to start which always gets worse after fixing the focus. Also this set is a devious little scoundrel, I had it going good and just started to put stuff back on top of it then the gun balance went intermitant the blue gun will completely go dark the red is close (only working with a red color signal, or a tweak of the screen control) the green is impervious to this....The balance likes to go bad when the color control is not set for a black and white picture. The CRT socket was still making arcing noises even after returning the focus voltage to speck so I think there is something wrong with the socket.

Tom. You probably have no choice but to replce that socket. It's all carbon-pathed inside. I was going to ask the same question. How is the trippler connected, to substitute the HV rectifier and the focus divider?