My Christmas day 9T246 restoration! Almost.....

[Kamakiri]

Decided to have a go at my 9T246 that's been "on display" since I picked it up over the summer. Powered it up on a variac when I got it, and while the raster was bright, the picture was a distorted mess. Today, as the wife was baking cookies, I went as far as the capacitors I had on the shelf would take me, and this is what I got!

Clicking the picture will take you to the video



Weird problem though. If I leave it on the channel that was on when I turned it on, the set is fine. As soon as I change the channel, the picture loses horizontal sync. Otherwise, I just watched a full episode of Gunsmoke on the thing.....

If I turn the set off for a half hour or so, then turn it on, the channel I left it on is fine.

Ideas/thoughts? Obviously I'm going to have to order the rest of the capacitors and finish the re-cap, but this is something I haven't seen before.

[Sandy G]

Dah-Yum, Tim, for just "Foolin' Around" that's pretty dad-blame good..

[Kamakiri]

I got lucky

[Sandy G]

Yeah, maybe so, but you're also pretty GOOD, too...

[DaveWM]

there is a rather involved setup of the sync, adj the horz coil top and bottom, then the sync drive cap. Clearly you need to to all the caps and would be a good idea to replace the domino style caps in the horz circuit as well.

[Bill Cahill]

You are also living dangerously with original electrolytics, and, those black beauty striped capacitors. I've seen them explode.
I've seen electrolytics explode, and, do other nasty things. I had one in a 9T246 that actually shorted to another section. Result. smoke for an angry resistor, and, the set still lit picture tube, but, lost all reception, and, I couldn't turn down brightness control. That circut was shorted when the cap shorted to another section.
If a filter blows, yo'll blow your resistor bank on the back of the chassis. Then what will you do??
Bill Cahill

[DavGoodlin]

Good Job Tim, you're on your way to working history. Lets see more.

[Kevin Kuehn]

That's looking pretty good. There's a good chance that replacing the rest of the caps will help the sync lock in better, then make the horizontal waveform adjustments as Dave mentions.

[M3-SRT8]

Yup. And make sure you replace the molded paper caps along with all the tubulars and electrolytics.

I would also replace the silver micas in the horizontal sweep section, as those seem to be failing nowadays.

Then, check the tubes and high value resistors, and tweak the set with a Test Pattern.

[Kamakiri]

So, basically, I just need to finish the job . Kinda figured that was the case, it's just that I've never seen something like that happen before. Left on channel, I had it playing for about a half hour with no issues. Change the channel at any point, and all of a sudden, bye bye horizontal sync.

Time to order capacitors

[Penthode]

I am still amazed that everyone in this forum insists on always replacing the electrolytics. The original electrolytics used in the RCA sets of the period will probably outlast the ones being stuffed into the cans!

It is a simple process reforming the dielectric and testing the things. I have replaced some electrolytics if they do not reform properly. The test is to ensure the leakage current remains below 100uA at full rated voltage.

Paper capacitors do leak and need to be replaced. When I get a set and before powering it up, I will test a few of the paper capacitors. If any show leakage (as they generally will) I will replace all of the. However, the electrolytics and micas are generally okay.

[M3-SRT8]

Originally Posted by Penthode

I am still amazed that everyone in this forum insists on always replacing the electrolytics. The original electrolytics used in the RCA sets of the period will probably outlast the ones being stuffed into the cans!

Hmmmm....No. I disagree.

You can get 105 centigrade rated electrolytic caps from Mouser that are light years ahead of anything they made in 1946. Cheap money, too.

Were the 'lytics that RCA used in '46 good? You bet. Are they any good now? Do you really want to roll the dice and worry about it? Plus, the micas in the hor sweep circuits are starting to fail. I habitually replace those now, too.

[Eric H]

Originally Posted by Penthode

I am still amazed that everyone in this forum insists on always replacing the electrolytics. The original electrolytics used in the RCA sets of the period will probably outlast the ones being stuffed into the cans!

Have you ever cut any of them open?
Most electrolytic caps from 1950 and earlier that I restuffed were dried out and crumbling, the foil was deteriorated and rotted not to mention the leakage between sections.

Occasionally I will find some that still work but knowing what they probably look like inside there's no way I'd feel comfortable using them.

[Phil Nelson]

Yah, the innards of 1940s electrolytics are usually nasty. The photo shows a can from my 1948 Capehart-Farnsworth 661-P.

That one came out mostly in one piece. Some come out with a bunch of dust and crumbly chunks.

I don't care if anyone else replaces electrolytics -- it's your TV, do what you like -- but I'm not comfortable running with that kind of component onboard.

Phil Nelson

[kvflyer]

Originally Posted by Penthode

I am still amazed that everyone in this forum insists on always replacing the electrolytics. The original electrolytics used in the RCA sets of the period will probably outlast the ones being stuffed into the cans!

It is a simple process reforming the dielectric and testing the things. I have replaced some electrolytics if they do not reform properly. The test is to ensure the leakage current remains below 100uA at full rated voltage.

....

Yikes! Did I read what I think I read? Sorry, I have to respectfully disagree with this as others have...