Another Project?

[Phil Nelson]

Originally Posted by leadlike

the contrast control is actually a gain control

The RCA 630TS has a manual gain control in front, labeled Picture control. Kinda weird until you get used to it.

Originally Posted by leadlike

The vertical and horizontal hold controls are in the rear of the set.

My DuMont RA-103 is the same. I was initially dubious, thinking the designers were just a bunch of showoffs. Turns out that the horizontal and vertical are absolutely solid, even with different video sources, changing channels, etc. None of my other restored TVs has that kind of stability.

By the way, did you ever clean the contacts in the tuner?

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[jeyurkon]

Originally Posted by leadlike

The vertical and horizontal hold controls are in the rear of the set. The literature I have been reading on this set describes these controls as something that only need be set up once, and then left alone. We'll see how much that is true once the set it running. I will say that the vertical height, hold, and linearity interact with each other a good deal. If that vertical hold control was on the front of the set, in the hands of the average Joe, you could probably really mess up the picture.

On my 1-108 chassis Sylvania the horizontal and vertical controls are underneath the chassis. Accessible, but not easily. Once set, they are very stable. The horizontal circuit is an RCA design.

John

[bandersen]

Nice job on the PS

Is you BK working well enough to inject video at the grid of the video amp (V7) ? That should allow you to get the sync circuits working and see an image. I believe you could inject a composite video signal here too for your A/V jack, but you'd need to play around with the level and polarity.

As for audio, you can add a jack at C41 on the volume control for AUX. Maybe replace that 2 position TEL / RAD switch with a 3 position one

[leadlike]

GEDC0167.JPG

Here is the kind of scrambled video I get when I feed in video from my B&K, my color bar generator, or even my dvd player into the grid of the video output tube. I can't sync anything. I'm just feeding this in with bare leads. Should there be a coupling cap, a diode (since this is past the video detector diode) or anything else needed to properly couple the signal to the tv?

I can't even tell if there is even a video image to pull from this. I just simply go from a flat grey raster to this mess when I feed anything in. Adjusting the output levels on the B&K does nothing but fade to picture to snow.

[bandersen]

That looks promising to me - you just need some horizontal sync. It should fade to snow as you drop the level. Have you tried flipping the polarity switch on the B&K ? Do the horizontal clipper, amp, discriminator, etc. circuits check out OK ?

Yeah, I'd use a coupling cap so as not to damage the video source. Maybe a few 100 pF. You don't need a diode if you're feeding in a composite signal.

[jeyurkon]

I'm not familiar with the set, but it looks like the horizontal frequency is way off. Have you tried to adjust the horizontal hold?

John

[leadlike]

Okay, after fiddling around with the horiz. sync on the television, it just mustn't be syncing on the Horizontal. The best I can do is get it to "lock" on a multiple of 8 repeated horizontal images of the B&K test pattern. Flipping the B&K's polarity switch makes the image go negative.

I've checked every single component in the horizontal output circuit, and I guess I'll start working my way back to the sync clipper, etc. Tomorrow night.

With the video if circuits working away, could that possible swamp the B&K's signal, considering the contrast control is a really a B+ gain control for the IF strip?

[Jeffhs]

Did you try adjusting the horizontal hold control? I agree with bandersen that all your set's picture needs is sync, and yours is way off. I'd try adjusting the control first, before pulling the chassis. That failing, I'd check the horizontal AFC, as it may be yanking the oscillator so far off frequency that even the hold control won't bring it back.

[leadlike]

I found an adjustment for the horizontal on the schematic (L21) and began twisting away. It functions almost as a course horiz. frequency adjustment, so the picture quickly pulled into sync a faint image of my B&K test pattern. Hooking up a dvd player revealed a scrambled mess of a picture. the difference in sources was enough that I had to readjust everything again. Now I have an image to play with!

GEDC0169.jpg

Vertical lock is pretty well nonexistent, but I am more concerned about the faintness of the image. For this tv, since all the contrast control does is ramp up the plate voltages on the IF, I will need to find another way to tighten up this image. retrace lines are everywhere, too, but the lack of vertical hold is probably contributing to that.

[bandersen]

Awesome! I had to make the same 'coarse' horizontal adjustment on my last set too.
Are you feeding the signal into the video amp tube or the antenna terminals ? If it's the video amp, perhaps the level is too low ? That could account for the lack of vertical lock too.

[leadlike]

It's being fed right into the video amp's grid. I would suspect that the piddling signal from the dvd player just isn't enough to drive a decent picture to the single video amp tube to the crt.

OTOH, the IF strip could be swamping the dvd signal. Should I pull the final video IF tube to drop this potential interference? Also, does the dual diode do anything for a signal added to the video output grid as I am doing, ie do I get dc resto?

[bandersen]

Here's a link to a partial schematic for the 802. The DC restorer comes after the video amp so it should be OK. Have you tried doing this using the B&K ?

Set the RF selector to 'IF'
Set the IF frequency to somewhere around 22 MHz
Inject the video signal at the grid of the 3rd video IF (pin 4)

Do you get a picture now ? (you may need to fiddle with the IF frequency). Is it any better ?
Likewise you can work you way back through the 2nd and 1st IF amps.

[leadlike]

I replaced some more caps and resistors, focusing on the vertical section this time. Nothing too terribly out of line, except for a mica cap (c136 from Banderson's schematic) was open. I've found a number of open micas in this set, something that I rarely find in other tvs.

I believe that the tuner has at least one open one in its signal path, hence that is why I have no fm or television reception. The service manual describes the tuner as "easily removed from the chassis for servicing" well, it took about two hours to remove the tuner, mark the dozen or so leads that needed to be pulled, and even then it appears to be physically impossible to get to those mica caps.

Anyway, back to inputing composite video to the video ouput grid. Here are some results:

GEDC0170.jpg

GEDC0171.jpg

The distortion in the first picture comes when I install the dual diode (6h6 on the schematic, but mine is a 6al5). Lots of nastiness sweeping from the left to the right.

When the 6al5 is pulled, you have the better looking result in the second picture. Vertical ALMOST wants to lock. I have a pretty good contrast balance, considering that now twisting the contrast knob just throws off the horizontal sync. I do get a bit of distortion-a pretty variable black shadowiness with jagged edges (not unlike a lesser version of what was happening with the dual diode installed) that changes size with the material on screen. I believe this may still be an issue with the horizontal lock, as the horizontal blanking bars have also been creeping in unless the horizontal is dead on.

[bandersen]

Weird that the 6AL5 would cause problems. Just curious - what are you testing the mica caps with ? I have a couple vintage capacitor testers that use a bridge and eye tube, but I don't really trust them.

[leadlike]

I have an old Heathkit cap tester. There was an online tutorial on how to fix this particular model, and I've never had any issues with it since it was recapped/repaired. Typically, when I test a cap, I test the potential new one going in, and then test the old one going out. In the case of the 240pf cap that was dead in the vertical section, it didn't register as anything on the magic eye tube.