I've made a bloody mess!

[veg-o-matic]

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

[drh4683]

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

[veg-o-matic]

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.

[andy]

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.

[veg-o-matic]

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)

[kc8adu]

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.

[veg-o-matic]

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!

[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.

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

[drh4683]

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.

[drh4683]

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.

[drh4683]

voltage chart

[drh4683]

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

[veg-o-matic]

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!

(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: ? Don't remember seeing it before.