WHAT was I thinking?
In regards to my Dumont, I decided to take matters into my own hands and see if I could get 'er running okay. I guess years of experience haven't meant a darn thing!
Anyway, I did a purity adjustment, and it came out all right, I guess. Then I started messing with the vertical linearity and height controls (I think) to see if I could get the picture in shape. Got some sizzling noise and loss of vertical hold from the linearity control and loss of vertical hold which I could fix with the "regular" vhold knob from the height knob. When I left it, the picture wasn't any better but it still filled the screen.
Then I went through the SAMs and decided to reseat the vert-mult/vert output tube (that's what it says. It's a 6GF7A.)
HUGE mistake.

Now what I have is a picture that only fills the top 3/4ths of the screen and consists of horizontal scrolling bars of red blue and green.
Looks like crap!
Bugs Bunny is no longer in color!
Never should have taken off the back!
I should know better!
Any ideas? I'm starting to think I should just throw a cloth over it and call it an end table.
Shamefacedly,
Bob

bob,

you lost your color sync. I remember seeing corrosion inside that set. Try rocking the color tubes around, color should pop back in. If not, either a defective 3.58osc.,reactance, or AFC tube is causing trouble. Should that fail to cure it, there are probably cracked solder joints on the PCB. The only thing I can think is that when you removed the 6GF7, the PCB pulled up and either cracked a solder joint or caused a tube pin to lose good contact. Be very cautious when pulling a tube out of a set with PCB (printed circuit board). If I remember correct, its just one huge PCB with no support on it at all, the entire board would bend and flex when a tube was pulled.
Flip the set on its top and pull the bottom cover off and inspect the tube socket solder joints very carefully, if they are cracked it will be a very fine circular crack around the pin of the socket. You need a sharp eye to catch it, so be patient. If you want, rotate the suspect tubes in their sockets while looking at the solder joints, it will help you pin down the loose cracked one as you will see very slight movement or opening of the cracked spot. Its no zenith thats for sure.

Good luck-Doug

Originally posted by drh4683
bob,
you lost your color sync.

What I've lost is my mind.

So for those of you who are just panting for the latest update, here 'tis.

Messing around last night. Looked for cracked solder joints but didn't see any. 'Course my eyes ain't what they used to be, so who knows?

Then I started rocking the tubes around in their little sockets. Not much happened until I got to the (ahem) "Chroma Sync Phase Det/Color Killer Det". No more scrolling stripes on the screen! I had Red! I had Blue! I had Green!

Not all at the same time, mind you. Seems I had my choice of a picture that was completely red OR blue OR green. Yeah, it's color, but not quite what I was aiming for.

Where to go from here? Wellsir, figuring that I couldn't make matters any worse, I yanked out all the tubes on the chroma board and reseated them. I noticed that the pins were somewhat corroded.

Okay, no more solid-color screen, but not much color either, so I went through the process of (I don't know what it's called) turning down all the screen controls, flipping the service switch on and turning the controls back up intil I got a line of each color.

Woo hoo! I got me some color now, boy! Could actually adjust for proper fleshtones.

Bugs is once again walking around on GREEN grass.

What I ain't got is a picture that fills the screen. The bottom fourth is still blank and I think the linearity is still off, no matter how I mess with the height/linearity controls (which, by the way, got cleaned with some contact cleaner spray. Didn't make any difference in what they do, but I'm not getting those sizzling noises any more, which is progress of a sort.)

Any ideas where to go from here? I'm tempted to either replace all the tubes on the chroma board (which seems a little drastic since they've hardly gotten any use) or just pulling the tubes again and cleaning the pins, maybe with a Dremel Tool or something. Does that sound like a plan? Or like a stupid plan?

And now there's a PINK Dualette up on Ebay that I have my eyes on.

Of course, it doesn't work.

You almost certainly have one or more bad electrolytic caps in the vertical section. They can dry out over time, even if not used. The best way to find them is with an ESR meter which measure the caps internal resistance. The other way is to temporarily sub a new cap for each cap until you find the bad one. There's also a chance of some off value resistors in the vertical section. Since the set was never used, I would be about 99% sure a tube isn't the problem. If you don't have a schematic of the set, I would strongly suggest getting one so you can quicly ID the caps used in the vertical circuit. They aren't always all located near the vertical osc and output tubes.

A bad electrolytic cap? ME?

Now for some stupid cap questions.

First, the SAMS lists about 2 pages worth of "capacitors", but only a handful of electrolytic ones. I'm hoping it's only this handful I have to track down.

Three of them are in big metal cans right on the chassis. I'm guessing they have nothing to do with my vertical problems. There's one on the convergence board, so I guess that one's out of the running too.

Now we get to what I think are the likely suspects. There's one on the video-sound board, but I can't find it on the (excuse the terminology) Big Roadmap of the set. The last one is a big fat cardboard almost-toilet-paper-roll-sized hummer on the chroma board right next to the vert mult/vert output tube.

Am I getting warmer?

Suppose I just go ahead and replace this. Capacitors can't be that expensive, can they? Or particularly hard to get?

More stupid cap questions:

I know you're supposed to discharge 'em before working on them, but how does one accomplish this?

What's the best way to remove one? Desolder from the top, or from the bottom? Resolder in the same place (top or underneath, I mean) ? I really suck at soldering so I'm hoping to keep it to a minimum. Apparently, I'm what's known as a "blobber".

P.S. What's an ESR meter?

Why do I feel like the Three Stooges theme should be playing???

Veg,
Just looking at your trouble- thought I would run something else by you check out. Do the VERT HT and VERT LIN controls both have a reaction when you turn them? Also, does the effect on the screen when these controls are turned look smooth or maybe a little abrupt? There is usually a fairly high voltage on these controls in a tube set. If you heard a sizzling sound inside them one of them may have arced over inside and have a bad spot. You might check any resistors connected to these controls too. If one of those controls was arcing it could have caused a resistor to change value or open up. Good luck.
Jeff (PUNK ROCK DUDE)

look for a big lytic near that 6gf7.

I've never seen a DuMont set from the late 60s.

I hope you get it working. I wanna see a pic of it with a good picture.

Did a little more work today.

I replaced the electrolytic cap that was in the vertical section--kc8, you were right on the money. It was right next to the 6GF7. Naturally, it was the hardest thing to get to as the opening in the bottom of the set is divided in half and one of the leads was smack dab under the dividing bar. Still, I managed to get the old one out and the new one in. I'm like the world's WORST solderer, so it was really cool when I saw it firmly attached.

Anyhoo, once I remembered to replace the tube I pulled to have some "poking-around" room (duh), I fired 'er up and nothing. Well, not nothing, but no change from before. Picture still doesn't fill the botom 1/4 of the screen. That's the bad news.

The good news is that I didn't break anything! Or explode myself! And I successfully soldered something! 'Course, I melted the insulation on a wire that had the nerve to get in my way, but at least I didn't melt it all the way through...

So. Any ideas where I go from here? I'm trying to drum up some vintage repair manuals but they're hard to come by around here and the ones I got mostly deal with transistor sets.

The wallpaper is up in the den. It's (mostly) shoveled out. I bought new chairs today. This TV is the last major project.

HELLLLLLP!:D

Veg-o-matic, I think you need the Photofacts...you need to get some voltage readings in the vertical section to track down the problem. After you have replaced the most likely defective components from a visual inspection of the area (such as electrolytics) you need the schematic with voltage data to do a good troubleshooting job.

I have found it impossible to fix the really tough problems without the Photofacts or at least the manufacturer's schematic.

I agree with chad 100%. I will check through my photofacts and see if Ive got the folder for that set. If i do, I'll give you some voltage points to check.

Bob, Ive got what you are looking for! INFORMATION!!! For some reason out of pure luck I have a factory Dumont service book that was in a box various tv manuals. I scanned the schematics, vertical section in perticular as thats your trouble area and a tube pin voltage chart. So have fun! Let us know what happens. For what its worth, if I knew you were getting this set, I would have fixed it all up and ready to go just like your zenith so you wouldnt need to go into all this. However, Its good experience and fun to fix a set yourself.

voltage chart

When you get it fixed, it should look just like this! Its called the "stamford"

Originally posted by Chad Hauris
Veg-o-matic, I think you need the Photofacts...you need to get some voltage readings in the vertical section to track down the problem. After you have replaced the most likely defective components from a visual inspection of the area (such as electrolytics) you need the schematic with voltage data to do a good troubleshooting job.

Oh, I've got the Photofacts all right. Ordered 'em right after I got the set. Went through 'em, and even found the likely electrolytic that I (successfully--Yay!) replaced. What I lack, though are

1. Testing equipment
2. Skill
3. Knowledge
4. Patience, dammit!:dammit:

(Pardon me a moment while I take some deep, cleansing breaths and find my center.)

Okay, I'm back.

Well, lacking all the above, I'm sending the tubes out to be tested. I know, I know, but at least it looks like I'm doing
something. And did you know that you can't go down to the local drugstore and test your tubes yourself any more? Next thing you know, they'll start putting BUTTONS on the phone!

Gonna keep plugging. Keep sending your tips, though! One of these days...

Bob

P.S. Is this a new one: :beatnik: ? Don't remember seeing it before.

The only test equipment you need is a digital multimeter (or analog voltmeter, but I find the digital is easier to read). Skill and knowledge only comes through experience! The more you do, the easier it becomes.

Troubleshooting always moves from the general or obvious to the specific or concealed. You took care of obvious potential problems such as electrolytics or tubes...that is the first step.

Now you need to start examining the DC voltage readings, starting with the most general...the power supply input voltage to the stage (+405 volt B+). Also it looks like the boost voltage (usually +800 volts or so) comes into this stage. Check the supply voltages against your photofacts. If they are off, then you know that the trouble may lie in the power supply circuit delivering that voltage.

If the power supply inputs are OK, now start measuring the voltages at the 6GF7 tube...check against the photofacts. If you find wrong voltages here, then you know what part of that vertical circuit has a problem.

Do not do component substitution until you have really narrowed down the problem. Checking the DC voltages against the photofacts WILL help lead you to the problem.

Well, it's too late to do anything about the tubes 'cause I've already sent them off. On the good side, a lot of what I've read seems to point accusingly to that 6GF7A vertical output tube, so maybe getting a new one will do something.

Digital multimeter, eh? Well, I guess the budget will stretch for one. Plus, they're small and a reasonably fun gadget so I'll go shopping soon.

Frankly, though, I just can't see myself patiently testing all these voltages in a logical manner. I'm thinking 10 minutes tops, then I go take a nap.:D

As for gaining skill and knowledge through experience, well, I can easily see myself getting a really bad perm before any of that "knowledge" stuff sinks in.

Case in point: I got hold of a do-it-yourself TV service book from 1969 yesterday. Looking through it, I see a how to discharge the high-voltage anode (??-- suction cup thing on the CRT). Okay, you attach one end of a lead to the high-voltage cage, then pull the suction cup and poke the other end of the lead to the connector. I'm thinking that lead ought to be pretty heavy duty, but there was no mention of it. And here's the kicker: the picture illustrates the process with the guy's arm leaning on the HV cage while he does it.

Heaven knows I'm no expert, but isn't that kind of...what's the word I'm looking for...assholic?

Well, back to the drawing board. If you don't hear from me for a while, send flowers.:sadwave:

Well, no real progress, but there's potential.

Got hold of an old book--SAMS Photofact guide to TV repair, or something like that. Bunch of screenshots of problem pictures with associated components to check. Easily the best repair book I've come across so far. Gonna hate to return it to the library!

Anyhoo, there's a capacitor that could be the troublemaker for my "doesn't fill the screen" problem. Found it and pulled it last night, though I don't have a replacement yet.

Here's a stupid cap question--do they all have polarity? The one I pulled is marked .47 +/- 20% 200WV EM. There's a small line of yellow paint at one end. Does that indicate negative pole, or am I screwy?

The SAMS book also pointed an accusing finger at a number of resistors, all of which are buried and almost un-getatable. Should I decide to take the plunge and pull the chassis (not a decision I will make lightly!), how exactly do I discharge the HV anode without making myself dead? I've seen pictures of people just touching the connecter part to the HV cage without using gloves or anything. This makes me nervous!

Though I only have a partial screen's worth of picture, I sat around and watched some (you guessed it) cartoons the other night. Even with the lack of height and the misconvergence, I was impressed by the quality of the picture. Everything was nice and sharp with nice, bright (here it comes...!)

LOLLIPOP
color!

More updates as events warrant!

Hello Veg a Matic,

1. Just electrolytic caps have polarity. Most caps of the value you mentioned don't have any polarity.
2. To discharge the anode of the CRT- The way I usually do that on a tube set is to take a long flat blade screwdriver and attach a test lead to it. Attach the loose end of the test lead to the chassis ground. Then very carefully slide the end of the screwdriver under the anode cap until it touches the metal connector underneath the rubber insulator. You will most likely hear a snap when you contact the connector as the HV drains away from the CRT anode.
Good luck!!!

Jeff

I've been shocked a couple times from discharged HV (never while on!). Discharged HV likey wouldn't kill you, assuming you're in good heath.

However, it will make you do other things...

Once when I was shocked by a Zenith roundie, my legs tried to stand-up while I was crouched inside a console. Needless to say, I banged my head HARD I didn't know whether to feel pain from my head, or my hand which received the shock, so I just did a lot of cursing!:rant:

You never forget a shock like that!!! I got shocked once by a Sylvania Hybrid set and I will NEVER forget that. I got thrown back into the wall! I had been discharging sets the same way for years and never once took a "bite" from any of them. I don't know why that damn set had such a high build up. Anyway.... I am such a wuss I have never discharged a set again. While in the shop I always made my grandpa do it! (now how nice is that????)

Did you ever get zapped when picking up a CRT thats not in the cabinet? When I did catarac repair on my zenith roundie, I almost dropped the darn thing right on the floor! The HV well touched the side of my arm when I was aligning it to fit back in the set. I too always did the screwdriver wire trick and it worked good, however if I didnt hold it long enough, there would still be a good zapping charge. Now I use my HV probe, as I can watch the voltage drop to zero, telling me its safe to touch!

The charge will re-accumulate on the CRT after the first time you discharge it...if a CRT anode lead is disconnected, the button on the tube should always be discharged again before touching.

I disconnect the test lead from the multimeter and connect the end that would plug into the multimeter to an alligator clip lead connected to the CRT ground strap...then I touch the end of the meter probe to the CRT anode to discharge it. The test probe seems to offer good insulation from the HV...have never got shocked using this method.

The only time I have gotten shocked from the HV was when I was removing the 3A3 from a Zenith set years ago...I touched the metal cap of the 3A3 (with the set unplugged) and the HV charge came back through the 3A3 tube somehow...should have discharged the CRT first.

I think it is safe to say that we who have been in this "hobby" for awhile, it's not a matter of if you will get a hv gotcha! but when. My 2 cents worth
Richard

Originally posted by Richard D
I think it is safe to say that we who have been in this "hobby" for awhile, it's not a matter of if you will get a hv gotcha! but when. My 2 cents worth
Richard

All righty then!

I'm already nervous just poking around inside the set--this discussion ain't making it any better!

I think mayhap I'll leave the chassis in the cabinet for the time being. At least until I can teach CPR to my weiner dog!

Hi, veg-o-matic, I did not mean to alarm you unnecessarily, you have a healthy respect for what you are working on and I would be very unhappy if because of my post you quit working on your gem. I think you will be fine, it's the person who trys to blindly charge into a tv chassis without asking for help that really scares me. You seem to be doing everythig right so please continue. Just think of how you will feel when you get it working perfect, and you will!
Richard:D

Just so y'all don't think I'm totally inept...

Mom expressed interest in having her bathroom painted. Took care of that and while I was at it, figured it was time to do other stuff it needed.

So, over the weekend I painted, ripped up the old toilet (generic, builder-grade) and replaced the white (!!) ceramic tile floor with good old-fashioned vinyl tile. Yeah, I know the ceramic was supposed to be something of an upgrade, but it was impossible to keep clean, especially the grout.

Oh. Installed a new toilet, too. Kinda important!

It looks quite lovely, if I do say so as shouldn't. Paint might be a bit too shiny, so I'm considering applying a matte glaze to tone it down a bit. Mom's happy with it as it is, but it's my house, as I keep reminding her!

My bathroom next.

No progress on the Dumont, though. Went out and bought some of that PB Blaster stuff to spray on the convergence controls but they're still frozen (though it did help me loosen the supply line for the terlet). I'm about ready to give up on this sucker. Anyone want to give it a good home? Just come on by!

Oh, and I won that Heathkit with the horizontal hold problem on ebay. Glutton for punishment? You betcha!