Hi Guys,

What observations, experiences or suggestions may you offer on sync (mainly vertical) with our vintage TV's when connected to a cable TV input source?

OK, the basics: my cable company (RCN) supplies fully digital cable service and we have about 325 channels. Yes, the vintage TVs are all tuned to the standard definition (not the HD) channels. Now, the broadcast channels such as CBS, NBC, etc with 3/4 aspect ratios are all pretty stable, and with some of my early TV's the standard definition cable channels which come thru is other than 3/4 aspect (such as CNN for example) are stable as well. However a couple of my sets (the Philco Predicta BarberPole and a Zenith Mayflower porthole) do a couple weird things:

PHILCO PREDICTA BARBERPOLE:
On some cable channels such as AHC, or Destination America, etc. the picture will occasionally roll upwards when a scene changes or if a very dark scene such as a nighttime shot is on, and I find that adjusting the vertical sync is very critical (hard to lock it in). Yet when viewing a broadcast station such as the local CBS channel the sync is just fine and no problem locking in. Once in awhile however, if the cable company runs a local set of ads the vertical may become a bit unstable and again roll upwards once or twice with critical lock in of the vertical sync. As soon as the main broadcast program resumes the sync is just fine and locks right in. When watching a DVD I never have any vertical sync issues whatsoever, so its only on some channels or certain commercials from my cable system.

ZENITH MAYFLOWER:
The vertical is very stable excepting when watching CNN or MSNBC or another cable channel with an other-than-3/4 aspect ratio picture (which results in a blank area at the very top and the very bottom of the picture) Sometimes when going to a commercial or switching to another picture, the vertical picture will tend to drop so that the blank bottom of the picture meets the bottom of the picture tube, but the picture doesn't roll. As soon as another picture comes on the screen, or if I switch to a broadcast channel like CBS the picture locks in dead center and is very stable.

I know that vertical sweep and sync circuits are different in the Zenith vs the Predicta. But do any of you guys know of possible common threads that may affect these two sets?

The horizontal on both are always perfect and well locked in! Also, this issues does not appear on my other two Predicta sets, which is a Tandem (which shares the same chassis as the BarberPole) and my 17" tabletop set.

Thanks! :D

-George-

What are you using for an RF modulator to go from the digital cable box to your vintage TVs ?

Does the trigger for these events seem to be sceen-to-sceen transitions within a program, or at the transitions from program to ad content or station ID? If they're switching away from 'network' fee to in-house ad server, there could be a clock issue between the two. Frame synchronizers on each input are now pretty much baked into most master control switchers, although they could be using a frame sync on the incoming "satellite" network feed (which probably isn't a satellite any more.) The frame sync will buffer timing problems, but perhaps not as seamlessly as your older sets would like.

There's also possibly a "digital black" issue, where the usual 7.5IRE set-up on black levels is now 0IRE. This may trigger the effect you're seeing. That variability may be within a program, or within different spots and bumpers outside of the 'content' of the show.

If you can hang a waveform monitor on a demod feed while you're watching, it could help reveal some of this. Being able to record the feed, while preserving 0 vs. 7.5 black and timing info, would be helpful too, but many recording devices need to fix that before they record it.

Of course, it could be something else entirely, too! :)

Chip

Ok, well I'm not using any ref modulation other than the cable box supplied by RCN. It's a Motorola switchable between channels 3 and 4. I have it set for channel 4 but it really doesn't make a difference. The coax cable runs from the cable box straight to the antenna connections on the Ty's. In the case of my Predictas I have the antenna input switches set to "local" since switching to distant would overload the front end of the sets.

Depending on the channel I'm watching, the trigger can be either switching a scene or going from program to local ad spots. This is true for both the Predicta Barberpole as well as the Zenith Mayflower, along his with the Zenith, the picture doesn't roll but rather drops down so the bottom of the actual image meets the bottom of the CRT. And of course remember that this only occurs with channels that are not transmitting pure 3/4 aspect ratios, such as CNN for example which transmits in HD which is down converted in the same HD aspect ration but in standard definition.

My gut is telling me the issue is at RCN and not really within the TV sets. There's something perhaps in the blanking bar that is going out especially when the tv scene is a very dark (nighttime image) or when switching to local ads that the test aren't liking, especially since the sync is all time based on these old sets.

I think I'm wondering if there is anything I can do to the input signal to get around this? I'm already running the signal thru one of those little boxes which eliminate those copy guards which now and then I'll see on a copy protected DVD. It does a really great job on those DVDs with strong copy guard, but I had kinda thought it would block any weird digital codes that RCN may be inserting to the blanking bar that may be affecting the Tvs

Any thoughts?...

George

Ok, well I'm not using any ref modulation other than the cable box supplied by RCN. It's a Motorola switchable between channels 3 and 4. I have it set for channel 4 but it really doesn't make a difference. The coax cable runs from the cable box straight to the antenna connections on the Ty's. ... I'm already running the signal thru one of those little boxes which eliminate those copy guards which now and then I'll see on a copy protected DVD. It does a really great job on those DVDs with strong copy guard, but I had kinda thought it would block any weird digital codes that RCN may be inserting to the blanking bar that may be affecting the Tvs

George

Please explain how you are feeding RF through a copyguard remover - I thought they typically have baseband inputs and outputs.

I would try arranging things so that only DVDs go thru copy guard, not broadcast signals.
If you're having problems in the vertical interval, remove the gear that messes specifically with the vertical interval and see where you stand.

Chip

I think I'm wondering if there is anything I can do to the input signal to get around this? I'm already running the signal thru one of those little boxes which eliminate those copy guards which now and then I'll see on a copy protected DVD. It does a really great job on those DVDs with strong copy guard, but I had kinda thought it would block any weird digital codes that RCN may be inserting to the blanking bar that may be affecting the TvsFor what it's worth, I was able to eliminate Macrovision-like interference on our cable system by routing the video signal through an inexpensive "video stabilizer" box.

The interference was present in a certain range of channels in our cable system and it affected some, but not all, of my vintage TVs (following no obvious pattern). With advice from some VK members I was able to view the interfering signal on my scope and confirm that the stabilizer removed it -- whatever it was.

You can read that full discussion here (http://www.videokarma.org/showthread.php?t=263915).

If you already tried this kind of stabilizer box with no improvement, then I guess I'm not saying anything you don't already know. It's annoying that cable companies are inserting junk that vintage TVs can't handle, but I suppose not many people are watching cable on 1940s & 1950s TVs any more.

Regards,

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

Phil I'm using a video stabilizer box that you described. Bought it on eBay because DVDs play flawlessly I'm strongly suspecting junk in the blanking bar from my cable company. And various vintage sync circuit designs handle it better than others. But now you mentioned i I'm going to recheck my objections to see if that box is inserted from the DVD player only or the line to the tvs! Worth a good double check!

George