some pics

CRT test good after brief wake up.

Is that a 24MC32? I'm working on one right now and my chassis looks just like yours. Mine's a 1966. I see that it's the "gel" PVA bonding that gets the green halo instead of the "mold" looking cataracts of RCA style PVA. My tube is a gel one too. Nice looking set, glad she's saved.

Edit: I just noticed the knobs broken off, I'll see how many spares I have left, I think I already gave them all away.

Great if you have any thanks :thmbsp:

yes thats the chassis number on the back.

Mark, I think the one you have is in slightly better chassis condition.

the whole CRT seems to have a slight greenish tint in addition to a slight green halo.

progress...

the color demodulators seem to be working, I have a loose focus lead (not sure if I knocked it out or if it was already loose, I had very poor focus until I pushed it back into the socket. The CRT socket is pretty loose on the tube so I have to be careful (it was loose when I got it). sound is good, sync is good. have to work the vert scan, prob a cap (there is a paper cap in there).

HV seemed a little low, about 21-22kv full on. Will have to look into that, maybe a low B+ maybe shunt tube (I checked the HOT current, about 220, but did not check th shunt 6BK4). the HV adj does work, just lacks head room. It looks completly orig, I see no evidence of any work being done.

I think I will try a new vert tube, and check that electro cap. then need to find the B+ and check it. This set uses a doubler so I guess if one or both of the of the doubler caps was a little weak the B+ could be down.

yep looks like the cap I was checking out is the one in the vert out cathode bypass. I will be replacing that automatically.

I will check the can caps with my cap tester, so far most of the zenith tvs I have worked on had good can caps.


there is also a "brightness range" adj pot called out on the schematic, I did not see one of those. on the chassis.

There are some of those white caps 1000v that I will prob get rid of, and one of the Black with red stripe, I will check it.

Not sure what to do about the focus pin lead. Any ideas there? just clean it up well and epoxy it in?

The fly looked good, no dripping wax or any of that nonsense.

I see the shunt tube has test points across a 1k resistor in the cathode circuit. I will assume a 1v drop is normal (assuming its still 1k). there is a 1.5meg resistor in the HV adj pot circuit, goes to ground. If that were to drift, I think it could cause the shunt to work hard, I will check that if the shunt voltage drop across the 1k it too high.

The finish on this thing is hard, like a photo finish, I don't think I am going to be able to make it look too pretty.

Oh I changed the video cathode follower which seemed to help the video some (the video amp did not). I am hoping if I can get the HV up the pic will be a bit brighter, its not very bright right now, of course the tube was a bit weak until it heated up, so its prob tired anyway.

found the test point for the shunt reg (right behind the damper tube). so I got the set on its side, service saver cover off, HV probe attached,HOT catode on the mA meter, and now a volt meter on the shunt test points. I will be firiing if of later after today to see where it is. I will prob just jump that vert out bypass cap for a quick test to see if that resolves the lack of vert sweep. I was thinking it could be a boost issue as well, since the vert uses boost voltage, so if the jumped cap does not work I will check the boost.

1.75v drop across that resisitor, equates to a 1.75ma, on other 6bk4 equiped set (the Packard Bell) they want that to be around 1ma, so I am going to assume this should be the same. So now I will poke around the shunt regulator and look for a problem. Not a lot there so I hope it will be easy. Maybe just try a new tube 1st? I guess it could be gassy.

what did the hv go up to with the shunt tube unplugged? Should be max 1 volt at minimum brightness, if its 1.75 at max brightness its way off. That like 30 watts dissipation through the shunt. That should turn that tube black fast.

did not pull the shunt tube yet. will do later.

I don't know about Zenith, but RCA lists shunt dissipation at 18 watts for most CTC-X(X) receivers. 6BK4 data sheet says 30 watts is the max.

disconnected the shunt tube, KV shot to 30kv so I have to assume there is a problem in the shunt. Tried a new tube, no change in Vdrop across the test points (1.7v) so I will focus on the few componets around the shunt, there is not much there so hopefully it will be an easy fix. 1st check will be that 1.5 meg resistor.

1.5 meg reads 1.7 so that is a bit out (5% resistor) but that does not seem far enough out.

I am going to see if I can get a direct read of the grid and cath voltage, I am thinking maybe the cathode is low, it goes to the 350v so I will start there.

It would seem that if the over all B+ is low the boost would be low also, but maybe the relationship between the two could be upset? The boost is the source (thru a resistance series and the HV pot) for the shunt grid bias.

hmmm, after checking the cathode (right at 350v) I decided to check the Vdrop on the shunt resistor again, it was 1v the .8v then .3v just kept dropping. the HV did not go up. the HV control pot is still working. Its like it was losing HV headroom. The fly current did not move off 250ma, dont know if that is right, but seems like its in the ball park.

going to let it cool down and try again. It still has the orig damper and HV rectifier tube in.

jumped the cap, no change, lack of vert, new tube next. Vdrop right around
.6v not sure why the inconsistant readings (trying to compare on the same brightness settings and scenes).

new vert out tube, no help, next will be a new vert osc. Darn it as a termistor in the vert height circuit, I hate those. From there it goes to the boost voltage, AND there is a .1 cap to ground. That would be a prime leaker.

May also explain the odd stuff going on at the shunt (a leaky one that gets worse with heat would kill the boost). that one will get subbed (I do that routinely on those white ceramic tube 1kv caps) they are about 50/50 on being good or bad with leakage. I am pretty sure they are just a paper inside.

Welcome to another time eating vampire. This one has all the best of the ones we have been fighting going on. I have a working set with this chassis and it is very stable. Be patient. Ill send you the sams when I get home.

yea, not typical zenith this time. I got a sneaking feeling I am going to find some leaky caps. there is surface rust on the chassis, makes me think its seem some dampness (in florida that is hard to avoid if not kept in an air condition enviroment 24/7/365.

lots of weak or leaky caps in this one, brown drops, a
.1 .22 and .47 all in the vert circuit, much better height now.

the contrast control seems to have no effect, I the video amp tube has a large value cathode bypass on the contrast pot, I think its in a can but hard to get at and hard to trace as I still have the chassis in the set.

still getting odd results on the fly, its back to 1.7v drop on the shunt, the cathode voltage is ok (shunt tube), but hard to get a reading on the grid, even my vtvm is too much of a load on the grid, when I hook up the voltage must drop cause all of the sudden the HV shoots up as the tube gets cut off. so I am back to trying to figure out why the grid voltage is too high, looks like I will have to pull the chassis out and see if I can figure out whats going on. sure seems like it should be that HV pot and 1.5 meg meg to ground. the HV pot works so I figure it cant be open, it just does not lowering the grid voltage enough to reduce the current thru the shunt.

I dont know why last night the shunt current started dropping, but I did not leave it on very long this time, so maybe its a heat related thing.

Huh, maybe I should replace the brownies in the vert circuit of my CTC-9. It's always had a slight lack of height, and the vert linearity could be better too.

i replaced the brownies on my ctc10 vertical circuit and the height and linerity came back just like new. steve

Thats why I like my cap tester, great for checking those caps, shows up weak ones vert quickly.

Interesing note on cap testers, this got me once so now I always remember to disconnect the video feed from the dvd player to the TV. I have no idea why but if you leave it connected, sometimes a cap will read weak (fuzzy eye opening) if one leg was lifted for the test (so one leg is still in the circuit).

There is a .1 1kv white tube cap that test ok but I can't test over 450v so I may just replace it anyway.

Not looking forward to pulling the chassis, it looks like its going to be a pita, lots of tied off wire cables. This seems to be a low end zenith based on all the missing (unused) adj pots on the back of the chassis, and the cheapie IF tubes (6BZ6 on the 1st 2).

Thinks its time to check the cathode voltages, CRT seems dark, even with the lower kv (22kv tops HV adj as high as it will go, still 1.6v drop (1.6ma) on the shunt tube) it seems like it should be brighter. The fact that I am not getting any contrast control makes me think the video amp is not right, perhaps cutting off the CRT. looks like I will have to pull the chassis soon to get much further.

a few more checks, the CRT cathodes 260v and the screen grid around 650v so all good there.

progress, at least on the picture, had a open cap in the contrast circuit, much better pic now. Purity and convergence all jacked up, prob from my flipping it around so many times, I may have bumped the static convergence, but the pic is much better. Purity is a mess, but I can work on that later.

the cathode cap was in a can so good chance the others in that can are bad (screen bypass on the video amp was one, not sure about the others).

replaced the cap on the shunt (.022 grid to cathode) thinking it may be leaky, it was not, no change in shunt current still high and hv low (21-22kv).

I am going to take another look at the 1.5 meg to ground in the grid circuit of the shunt. It now seems like that is the only thing that could account for to high a grid voltage, unless for some reason the boost voltage is way, but not sure how that could be.

HV progress. I think I had incorrectly check the 1.5 meg to ground, I jumped in a 2.2 meg and everything works as it should. Can't say for sure that the 1.5 is bad and my 2.2 is just compensating for some other problem until I get a sams resistance reading as I think there are other part making a in circuit reading inconclusive.

If I had pulled the chassis to check it I prob would have found this a while ago, its just a major pita.

Maybe I'm wrong here, but 22kv sounds fine for HV. All my RCA sets run at 22.5, so you can't be too far off base...

well if were not for the setting being at MAX hv yes I would prob be ok, I like to have some adj that lets me set it a little above that with room to spare.

The other issue was the excessive current thru the shunt tube, that is normal now.

I still need to check the HO current with the new setup. If the resistor does indeed check to have drifted I will have my answer. After that I will address the HOT, and any excess HV being made. One solution would be to increase the screen resistor a bit to lower the overall HV to reduce the shunt load to around .8 to .9 mA and have HV up to 24kv.

The screen resistor seems like the way to go to deal with increase line voltages. I am somewhat hesitant to just go re-engineering these old sets, but if the line is consistantly 125v it may be worth putting in some easy to reverse change to make it more friendly to modern Higher voltages.

Of couse the easist approach would be to just use the variac, which I do on some sets that get a lot of time.

These round tubes were meant to be operated at 22.5kv, so there's no good reason to put 24 on them.

yep sams says 22.5-23.5kv. I have to scan the sams, do it tomorrow. Got stuck exploring the abandon prison and got home late.

Seems perfectly happy at 110v still holding at 23-24kv with reg current down to about .9ma, HOT current dropped to just under 200ma at the reduce voltage.

That was with the shunt grid resistor jumped, without it, the max HV was 19k and the shunt tube was 1.3ma at the reduced line voltage. I hope to pull the chassis sometime in the next few days to do a proper check/fix of that and also check/replace any other faulty caps (like that video amp cathode bypass cap.

Just trying to decide best way to pull the chassis, will have to make notes of lead dress etc... as there are wires all over the place, tied back to various points, a lot using the CRT mounting for tie points.

almost got it out, not as bad as is it seems, the UHF has the power switch and most of the hard wiring back to the chassis, I can leave the VHF in place and just disconnect the IF, AGC, B+ and filament leads. Have one less piece of stuff dangling. I am sure there is a way to mount the UHF and all the pots to the main chassis, maybe that will become obvious once I pull it back.

whew that was fun, its out now, that pesky 1.5 was reading 2.2 and its a 5% so I guess that was the problem after all. going to be testing cans, but my guess is they will all need to be replaced. On stuff I dont care about how the cans look, I generally just bone saw off the can and stick radial caps down from the top, that is the fastest way and keeps all the lead dress untouched.

Since no one will be seeing it anyway I generally do not bother to put the can back on top. effectively the can bottom acts like a term strip with the caps mounted on the top.

Most of the chassis I have done work to have the cardboard covers, maybe you could have someone send you a few to glue over the top of the stuft cans?

generally yes the doublers have the cardboard, and I do exactly that when I have extra covers.

So far the 1st can 4/4/100/200uf 475/475/475/50v only the 100uf 50v was open, the rest test like new. For now I am just going to bridge the 100uf and finish checking the rest. I am bit short on my 450v caps, so the plan will be to check the remaing cans, and see if I can get it going, then I can make up an order and get the proper caps.

well every other can cap tested fine, oh well nver hurts to check. I have checked all the brightness stuff since the CRT was a bit dim, all looks good. So to recap no pun intended,

200mfd 50v cap on video amp tube.

1.5 meg resistor on shunt tube.

I cleaned up the pot controls, including the on off volume that was inside the uhf knob it was sticky.

I sure hope there is no diddliing needed, the coil forms have what looks like dried cheese in them, my guess is the forms have started to break down.

I will put it all back together tomorrow, set it on the variac (to keep the HOT current low, use 110v ac line) and do a complete setup.

hmm the only thing I did not check was some of the caps on the convergence board, there was a bumble bee in there as well as one of white tube caps. I will check that out as well, my guess is the bumble bee will be leaky.

Anyone have exp with the yokes with the fishing line coming out of them? from what I read there are for centering the pic, but I have never had a set with them.

I sure hope there is no diddliing needed, the coil forms have what looks like dried cheese in them, my guess is the forms have started to break down.

Old wax, my CTC-7 had that going on too. Hit them with a hairdrier before you attempt to adjust them, or the form will get damaged.

Sense the crt is weak this would be a good candidate to increase the HOT screen resistor. Right now you just got a lot of HO wattage being wasted in the shunt tube because the crt cant use it.

It would be a good set to experiment on. You should be able to get the cathode down around 200ma or lower at line voltage and not see a performance change.

yep may try messing about with the screen resistor. I still need to fix the focus pin lead on the crt socket

drilled the rivuts, pulled the back off, careful not to let the other pin sockets come loose. the old focus connector remants were completely corroded, fell apart as I pulled it out. I was able to find a connector at rat shack of all places...

got it all back together used some small allen machine screws to hold it togehter. I will put it back in the cabinet tomorrow and see where we are, I am always a bit concerned after pulling a chassis that I have upset wiring under the chassis, so I try to be extra careful how I handle it so as not to push some part into another.

got it back in the set. Aftef fiddling with it forever I finally got it working again, a color amp tube is very touchy, I will need to clean the pins it took a lot of messing about, but looking pretty good. You can see the blue gun blooming so I will try some more setup. Plus the yoke is a tad crooked, so I will go back and straighten it out, but its not bad, def watchable. I just hope at some point CRT rebuilding become avail again. I think if the CRT was strong it would look great. I will snap some pics later after I get the yoke done and get the chassis all back togehter.

screen pics

Looks pretty nice to me!

That does look pretty good. Your CRT can't be THAT bad! :-)

Looks good, how does it look with the Simpsons ? Do you get the red bleed? (thats my test now)

left it on for a while, checking the CRT. after being on the CRT tester for about 45 min I rechecked the emissions and tracking all very good. I don't get it but I am not going to complain. I need to get this one in and just play it. The only issue I have now is the lack of range on the hue, guess it could be a pot, but will check the quad diode tube (think it has one of those) in the chroma circuit. the hue pot is very touchy, have to keep it full CCW and mess with it or its too green (never gets magenta, just right at max CCW).

Damn, but that's good color.

there is a coil that it says to adj for hue range, will be checking into that and see.

ok decided to check into the hue issue, 1st check some caps and resistors around the phase detector, all good. I had the set on its side and was going to tweek the burst amp coil to see if I could get better hue range. so I had it on its side, powered up, no pic, I hear static, I look at the back and I see sparking at the filaments :tears:

I have no idea what happened, I layed it on its side very gently, no bumps etc.. I check the CRT with a CRT tester, I see one filament glow weakly them more sparks then nothing.

filament pins read 30k I tried checking the even went so far as to try to resolder, no joy, break away the socket to get at the filament wires, nothing.

I tap around the neck (not hard) and I see a crack around the neck. I hear nothing at all, on air leakage etc, and it is an open crack (I can lift the neck off). So somehow it was either cracked and gone to air, or had gone to air and then I cracked it. My guess is it had gone to air before I cracked it, the filaments just burned out, otherwiise I am sure I would have heard something.

Anyway the CRT was very weak, took a good 5 min to produce a decent pic.

I had a spare CRT that I had planned for another project, but since it was no where near being ready (a CTC 7 with a very ruff chassis, may be a lost cause anyway) I decided to go ahead and use it. It the kind with the separate lens (no cat to deal with :yes: ) after struggling with it for about 1 hour I managed to get it all in an buttoned up. I touched up the purity and did a real quick static convergence (on over the air broadcasting not the dot bar gen) just to get it in the ball park. I have some vert bars on the left so I will need to look into the HOT/Damper and will recheck all the setups, did a quick gray scale setup. it looks very good, the pic quality and brightness are much much better and the pic is good to go in about 30 sec vs the old CRT 5 minute deal.

Not sure what happened but all ended well. I will get some more screen shots later after I take the time to do a proper setup.

something I have not seen before, the brightness seems a little greater on the top of the pic than on the bottom, maybe its just a linearity setting but I seem to recall reading about this kind of issue and diodes in the blanking circuit but not sure about that.

My guess is the better CRT is allowing defect to be more noticable now.

I am SO glad that a good thread on a Zenith of this vintage is here. I was posting before Christmas about finding a metal cabinet Model 5111, but I got sidetracked in going back to work on my 59 Space Command 24" B&W. There is so much good information here, a lot of which leads back to the same old same old, bad capacitors. Right now my Zenith starts smoking when the DC comes in; it's somewhere in the vicinity of the red hot horizontal output tube which I must keep the anode cap off of to eliminate the smoke. I already mentioned this in another thread, so I don't want to seem as if I am stealing the thread. When I get time to get into mine I think that I am simply going the route of pulling the chassis and replacing the paper and electrolytic caps and checking the resistors. I think with this approach I will find the road to a decent set a lot easier because I honestly don't know anywhere near as much about vintage color sets as I do black and white sets. There is a lot going on in an old color TV chassis, but I figure as long as the circuit components are in working order, then I should have a good old Zenith. I don't possess the equipment or the knowledge to worry about producing a perfectly aligned and pure picture, so I hope and pray that nobody has been in there adjusting things that shouldn't be adjusted. Actually, my set has all stock tubes, so I feel that it has been dormant for a VERY long time. I think that the last owner told the guy who gave it to me that it worked fine back in 1980. It's just been asleep too long to bring back to life without major surgery. If I tried to shotgun repair it, I would probably drive myself crazy with all of the problems constantly arising and end up hating the set. I say re-cap is the way to go, on this one anyway.

Not sure of the vintage of yours, but there are not a lot of paper caps in this one. The whilte elmento tube caps are the ones that may cause trouble but chances are they are ok. They are rated 1000vdc think there are 4 in there total.

The can caps are often fine. If the HOT is red plating the most likely cause is no grid drive since that is how it gets its neg bias. As a min you should check the cathode current, should be around 210-220ma(I use a socket that plugs into the socket, and has leads where the cathode is for connecting a meter) of the HOT, AND check the 6BK4 cathode current (there is a test point for connecting a volt meter so mearuse the voltage drop, should be around 1vdc drop), AND check the HV with a prob, should be around 22-23kv.

all those are related, if not working then I would start by checking the horz osc tube, its a triple triode compactron, if its defective there will be no drive to the HOT and red plating will occur. Sometimes you just need to wiggle the tube around some.

For general checking out of B+ I pull the HOT out of the circuit completely. I read somewhere that just disconnecting the plate lead is not a good idea, cant recall why.

With it pulled you can check the B+ current draw, should be very low. I generally do this with a metered variac, I pull the hot out, and the vert out, then do a very slow powr up. the variac I have has a voltage and currrent meter so I can see whats going on. Start slow and watch for current. I start out at 10vac just to see if the PT is shorted, then slowly ramp up to about 60-70vac over a period of time, again watching the AC current, again with out the HOT in it should be very low, around 500ma IIRC by the time I got to 70vac. I stop there since with no HOT load the B+ will go higher than the rated voltage of the can cap (I monitor the B+ voltage as well with a DMM while doing this, stopping when I get to about 375vdc, which will be well below line voltage). If you are just pulling the lead from the HOT and plugging it in to full line voltage, then the B+ will surely overshoot the voltage rating of the can caps, not good.

Miniman82 states “Maybe I'm wrong here, but 22kv sounds fine for HV. All my RCA sets run at 22.5, so you can't be too far off base...
These round tubes were meant to be operated at 22.5kv, so there's no good reason to put 24 on them.

CT17 states “ yep sams says 22.5-23.5kv. I have to scan the sams, do it tomorrow. Got stuck exploring the abandon prison and got home late. C17”

Sams RCA 21CT55, CTC2B says “..set HV to 25K. HV Reg 6BD4 cathode should read .7ma”

RCA Field Service Guide CTC2B schematic shows 25KV, RCA Service Clinic says…
“…6BK4 regulates HV voltage to 25KV which is required at the ultor of the 21AXP22”

My CTC2B uses a 21FBP22 which RCA max specs at 27.5KV. I now use the OEM flyback used in the CTC20 which also uses a 21FBP22.

CTC4 with 21AXP22 schematic shows 25KV, CTC5 with 21AXP22 shows 19.5KV!!, CTC7 with 21CYP22 shows 23.5KV, CTC7 with 21CYP22 shows 23.5KV, CTC9 with 21CYP22 shows 22.5KV, CTC10 with 21CYP22 shows 23.5KV, CTC11 with 21CYP22 or 21FBP22 shows 24KV, CTC15 with 21FBP22 shows 23KV, CTC16 with 21FBP22 shows 25KV and finally the CTC20 with 21FBP22 shows 25KV.

The only good reason to use an ultor greater than 22.5KV is to produce a better picture.

The only good reason to use an ultor greater than 22.5KV is to produce a better picture.


Really? You're still hung up on this? :thumbsdn:

Like I already told you in the other thread, there are better ways to get a better picture on the screen than stressing the already taxed HV section. Stripping out the matrix and replacing it with something modern like component video is one, installing a modern IC-based video section having a comb filter is another. Increasing HV only attracts the electrons from the gun 'harder', and puts stress on irreplaceable components like the flyback. I won't discuss this any farther on this thread since it's OT, either post about it in your thread or PM me.

over lunch I pulled the replacement CRT yoke and replaced it with the orig yoke that came with the set. I orig did not do this since it was stuck on pretty hard and I REALLY did not want to end up breaking another CRT two in one day would have been pretty hard to take. The Yoke that was on the spare CRT (both zenith) had a different PN. I had some jail house bars showing on the CRT and was thinking maybe there was a different anti ringing network in the yoke, plus I would rather have the orig yoke in place. I did not get a chance to run in and look for the vert bars, hope this takes care of it. wil of course have to re do the purity and setup again.

Not sure of the vintage of yours, but there are not a lot of paper caps in this one. The can caps are often fine. If the HOT is red plating the most likely cause is no grid drive since that is how it gets its neg bias. If you are just pulling the lead from the HOT and plugging it in to full line voltage, then the B+ will surely overshoot the voltage rating of the can caps, not good.

Hey thanks for the tips on this one! My 5111 is supposedly a 1964 model. I don't have a Variac, as well as a lot of other needed professional equipment. However, initially I used the 100W incandescent lamp method for at least a chance at a slow start. The reason that I disconnected the anode cap of the HOT was due to the smoking which started before any recognizable HV was produced. I knew that it would disable the circuit so I could see what might be going on in the rest of the circuits as far as overheating transformers, cans, smoke, etc. I had no idea that it could hurt my electrolytics. Seems like they would have engineered the voltage ratings higher if an open in that area could cause such damage. Luckily, I have never applied line current for more than a few minutes, and only a few times.

I'll tell ya, some of you guys blow my mind with your extensive knowledge of what is more or less a lost art. There is really no school that you can go to in order to learn what some of you guys know! Miniman82 made the following comment concerning video, "Stripping out the matrix and replacing it with something modern like component video is one, installing a modern IC-based video section having a comb filter is another." I was very impressed with someone knowing what it would take to improve or perfect antiquated circuit designs. I am an electronics student (at 41) in my final semester, and they just don't teach what I call REAL electronics! Thank God my dusty trail goes back to HS electronics back when we used Simpson analog meters and were taught at least rudimentary understanding of oscillators, detectors, etc. Now we learn the extreme basics of the full wave bridge rectifier using low voltages and current, controlling electromechanical relays, and lighting LEDs. I am scared to apply for a job based on that! Now we will possess the valuable knowledge of PLC programming and three phase applications. I guess that is their main focus to market us for employment.

I love bringing in old stuff and watching everyone but the asst. professor watch me work as if they were not even an electronics student. Even one of the few remaining Simpson meters will confuse everyone. I am just guessing that some of you guts have just been around long enough to have worked in electronics when it was truly electronics and less solid state, IC, riddled junk. Either way, I am glad to have contacts like all of you here and this great site. When I find a good job in the industry I plan on being an official member! :thmbsp:

the most likely reason for the smoke was lack of drive to the HOT, you should be able to get a DMM reading on the grid of the hot, think it should be around -70v (neg to the chassis, positive to the control grid of the 6JS6).

My guess would be a bad horz osc or some cap in that circuit. The main thing to do is to monitor the HOT cathode current, if it goes over 260ma then you have a problem, no need to try anyhing else until that is under control.

Yes the caps have some over voltage in the ratings, but they are 45 years old so no need to test that rating :)

Just go slow, read read read, get some old manuals off the net.

using the old yoke took care of the jail house bars, got the dot bar out and did a better convergence and set the lineairity. Looking pretty darn good. the convergence board still has on of those hard white caps (.056 10%) and a couple brown drops, and it still has the old Se quad rectifier pack, but I had to put it all away so the wife could have the garage back (tucked the TV over in a corner for now).

Thats interests me why the yoke caused that unless it was a total impedance mismatch or if there is a cap in the yoke thats bad. The impedance is a definite possibility as the set that crt came out of had a totally different style chassis.

Tubejunky, I would avoid the shotgun recap at first, you may cause more problems that you have. First thing is find were the smoke is coming from and go from there. It could be anything from the flyback arcing to the no drive because the pins in the drive tube are not making good contact in the socket. Some pictures would help too, good ones of the chassis and where the smoke is coming from.

DaveWM, Do you recall what the Radio Shack part number for the pin/connector that you used for replacing the corroded one on your CRT socket is?

nope, it was just one of those 4 place white female sockets, looks a lot like the stuff you see in the old zeniths

well I guess I should keep the 21FJP22 jug with the cracked neck (all down right near the pins). I can throw it up in the attic, should be safe from moisture up there (it get so hot it the summer that even in FL the humidity bakes out every day). Some day it may be repairable.

nope, it was just one of those 4 place white female sockets, looks a lot like the stuff you see in the old zeniths

Oh, like those AMP/Molex types..Seems like some sockets are more prone to this than others, and just because you have a certain chassis doesn't necessarly dictate what socket was used. Yea, I know that supplies on hand can and have changed through production runs.

I've seen this problem before with the style of socket that has the red phonolic back piece on it and rivits-secures near the center. Is this the type of socket you have? Just wondering...

I started looking at a Zenith 25LC30 and that focus pin must have been bad for quite a while as the CRT pin was corroded up too (cleaned up okay-whew!). I took my time slowly prying the two apart. I have not pulled the socket apart (yet) but it appears to have some signs of getting hot.

Not wanting to take away from your thread, but an observation to pass along.

yes this had the phenolic red back. I drilled out the rivuts and used some maching screws to re attach. the pin and socket were very corroded, had a heck of a time getting it to come off, extreme care of course to not damage the socket (not that it matters now since the tube went to air).

OMG, what a depressing thread!
I just took a 24MC32 home yesterday (My first roundie - I'll post on another related thread after taking inventory and pics). In fact, seeing this thread, I briefly thought I got stuck with DaveWM's old TV (but realized the legs on his set are different then the one I got).

I guess I'm in for quite a project.

One question - I see two completely different sets of Sams Photofacts for this chassis - 769-4 and 804-4. Which one do I want? Do I need both?

zeniths are a push over, I just went out and fired mine up yesterday, working fine. had a bit of retrace lines showing up in very low contrast scenes, perhaps a tube, or maybe just the RC circuit used off the vert out to cut off the video amp tube.

anyway mine is a mess cabinet wise, I am thinking of pulling all the chassis parts out and knocking out the 1/4 wood sides and top, replace with some real plywood and stain/finish. the faux grain is really mucked up.

do watch out pulling the CRT plug, the focus pins are often stuck (corrosion).

Really glad to hear that! I thought your story ended when your CRT went to air.

As for your cabinet - I notice that the plate behind the top of the VHF knob has the exact same scrape pattern as mine, LOL.

oh it did, big time, thats where a spare CRT comes in handy :yes:

yea its really really grungy. plus I am missing several of the plastic control knobs, but I may be able to scrounge up a few of those.

I could go the easy route and just try the stick on veeners, its been sitting for a while so it can set for a bit more while I think about it.

One question - I see two completely different sets of Sams Photofacts for this chassis - 769-4 and 804-4. Which one do I want? Do I need both?[/QUOTE]

The 804-4 is the "late production" version and the Sams is dated 3-66. Hopefully someone else will chime in here. I could be wrong but I believe the differences was with the IF's and tubes used? 1st and 2nd IF's used 6BZ6's and the earlier versions may have been the 6EH7's instead?

mine has the 7pin 6BZ6's.

geez, I dont know if I should

A) attempt a redo of the fake wood grain (one of those rubber simulated wood grain applicators that I have never used.

B) glue on some veneer.

C) replace all sides with some luan (sp) plywood.

D) nothing.

C is the most drastic
D is the easiest
A is the most learning
B is prob the easiest that will have a better look that it is now

Took another look at the set (Zenith 5317U) this evening. The IF strip is (6BZ6)=>(6BZ6)=>(6EJ7).

I've had this thought about avoiding the stress on the CRT from forcefully pulling the CRT plug off.

Would it make sense to sever every one of the wires going to the plug, marking each wire at both side of the break for identification, pulling out the chassis (and/or testing the CRT) with the plug in place, then stripping the ends of the wires and joining them back with wire nuts when finished?

I've been thinking about this for some time, as I have another set (B&W, so not on this subforum) with a disintegrating yoke, but I may need to remove the chassis to replace caps behind it,

BTW - The story of my roundie continues on another thread "Zenith Roundie in Detroit"

you should not have to go to that extreme, a good shot of some penetrating type contract cleaner around where the CRT plugs in, let it set over nite, then just make sure you hold on to the CRT plug base and slowly rock (not twist) the back plug connector off. Also use your thumb to apply pressure to the midde key of the CRT connector while working the connector off.

If its really stuck badly it maybe the focus lead corroded, in which case you would have to deal with that anyway. Patience and working slowly is the key.

you should not have to go to that extreme, a good shot of some penetrating type contract cleaner around where the CRT plugs in, let it set over nite, then just make sure you hold on to the CRT plug base and slowly rock (not twist) the back plug connector off. Also use your thumb to apply pressure to the midde key of the CRT connector while working the connector off.

If its really stuck badly it maybe the focus lead corroded, in which case you would have to deal with that anyway. Patience and working slowly is the key.

Dittos to the above plus you can "gently" use two small screwdrivers at opposite ends and pry between the two. Take your time here of course and after a little loosening you can detect where the most tightness is (focus pin) and move the screwdrivers closer to that pin on each side. The socket should come of uniformally/parellel as much as possible.

The 804-4 is the "late production" version and the Sams is dated 3-66. Hopefully someone else will chime in here. I could be wrong but I believe the differences was with the IF's and tubes used? 1st and 2nd IF's used 6BZ6's and the earlier versions may have been the 6EH7's instead?

Okay, I got the facts today - in both the "early" (as in 769-4) and "late" (as in 804-4) versions of the 24MC32, the IF strip is the same: (6BZ6)-->(6BZ6)-->(6EJ7/EF184). In fact, the whole tube complement is exactly the same. I saw one difference in the "tube layout - top view" on 804-4: It shows the vertical out as a 6HE6 instead of a 6HE5 - but even this is a typo, the schematic has 6HE5 and I can't find anything on the net that says a 6HE6 even exists.

The photos do show a different convergence board. The "early" shows a rectangular board about the same shape as a traditional TV screen above and to the right of the CRT neck. The "late", more like a "16:9" shape directly above the neck. As my 5317 has the squarer board, and a black HV cage, I'm assuming mine is an "early" (the picture of the "late" shows a shiny HV cage).

Differences in circuits were hard to find. One I found is where the brightness control is wired into the circuit. In the "early", it is between the delay line and the grid of the video out tube, whereas in the "late", it is soon after the detector, before the grid of the "cathode follower".

I would like to see them, i live in winter Park.